Let there be light. For without light, there can be no photography. Photography is the art of capturing an image of a scene in such a manner that it can be viewed in the absence of that scene. The sine qua non is a visible light-sensitive material (call it “film” for now).
In part 1 we will look at what is needed to make black and white film and how to make prints from the resulting exposures. Obviously, as of the Ring of Fire, Grantville had a limited supply of up-time film, and once that runs out, if we can’t make a substitute, the up-time cameras will become expensive paperweights. In part 2, we will consider the much greater complexities of capturing and printing in color. Finally part 3 will examine how cameras are constructed and how lenses are designed and made.
Grantville Literature on Photography and Photographic Chemistry
Unfortunately, it is very difficult to ascertain what books would have been in the school and public libraries as of the Ring of Fire (2000). Virtually all of the relevant books listed in the North Marion High School and Mannington Public Library (MPL) catalogues are 1) on digital photography, 2) published after the Ring of Fire, or 3) accessed as ebooks, and thus accessible only if a local copy was downloaded.
I assume the availability of the Encyclopedia Britannica, 9th edition (1902, EB9) and 11th edition (1911, EB11), with useful articles on photography, lenses, aberrations, etc., and of the 15th ed (EB15) (I have the 1999 release on a 2002 CD). I occasionally consulted a post-RoF edition of the Encyclopedia Americana (EA) just to get a sense of its depth of coverage. There are other general-purpose encyclopedias, too, but I will leave to others the task of finding and reviewing pre-RoF editions.
MPL presently has Davies, The Encyclopedia of Photography (Feb. 27, 2000); it’s iffy whether it was acquired before the Ring of Fire. But I would consider it reasonable to assume it replaced an older encyclopedia. Still, many encyclopedias and histories of photography (e.g. the post-RoF Abrams 2004 and Rosenblum 2007) are worthless for our purpose because they concentrate on famous photographers and their photographic compositions, or on shooting techniques, rather on film and camera technology. An exception is the Focal Encyclopedia of Photography; Kerryn Offord has the 2nd edition and I have the 3rd (1993). Note that there are subtle but important differences between the two, and this is a common phenomenon with reference works!
The people who are most likely to have books on darkroom technique are those who were art or journalism majors in college. Even today, a large number of schools still have courses on black and white darkroom photography (Hart). Darkroom users are also likely to have one or more manufacturer’s formularies since they were distributed for free or at nominal cost by manufacturers (Kodak, Agfa, Fuji, Ilford, etc.) hoping to sell the photographic chemicals listed in the recipes. However, there was a gradual transition, beginning in the 1950s, from selling individual ingredients to be mixed by the photographer, to selling “packaged” developers, etc., and the formularies would not reveal all of the ingredients and proportions of these premixed products. Some formulae would still appear in photographer’s handbooks, like Sussman.
Amateur photographers may also have books on the history of photography (e.g., Gernsheim 1986) that say something about how photographic emulsions or cameras were made at various points in history. However, it is difficult to guess which books they have. Perhaps one or more of the 1970 Time-Life series of books on photography (The Print, The Camera, Light and Film, Color, etc.), although I thought other likely sources were more informative.
There’s also the question of the chemical knowledge necessary to reproduce the chemical agents identified in the photography books. In my “Industrial Alchemy” articles, I assumed the presence of the 1968 Merck Index (MI), the 1971 Condensed Chemical Dictionary (CCD), and two common organic chemistry textbooks (Morrison & Boyd, and Solomon), as well as the CRC Handbook.
Kerryn Offord has proposed that one of the dozen or so up-timers with a chemistry degree might have a one-volume encyclopedia of chemistry. If so, it’s probably an edition from when they were in college or immediately after. He suggested Hampel (1973). However, I checked another encyclopedia of chemistry which was less informative, so it’s luck of the draw.
For the benefit of prospective authors, I provide additional information that is “not in Grantville literature” but which could eventually be discovered by experiment or mathematical analysis.
To properly expose an image, we must match the combination of the film speed and the exposure to the scene/subject luminance. And there are some standard terminology and concepts which we need to know in order to talk about the relative merits of films and cameras.
In the mid-twentieth century, measurements of the light sensitivity of film were standardized by the American Standard Association (ASA) and later the International Standard Organization (ISO), so we speak of a film as having such-and-such ASA or ISO. The higher the ASA (ISO), the faster (more sensitive) the film.
We can quantify scene luminance with a light value (LV). LV0 is the light level that requires a one second exposure at a lens aperture of “f/1” (see below) with ASA/ISO 100 speed film. Each unit change in LV represents a two-fold difference in luminance.
As a rule of thumb, a standard “gray card” (18% reflectance across the visible spectrum) viewed in “full sun” is about LV15. Open shade is LV13, a nighttime interior with average lighting is LV7, a night scene lit by streetlights perhaps LV2, a rural landscape under a full moon -5, and one under starlight, -15 (Rockwell).
The light-gathering power of a lens is dependent on its aperture, typically expressed as a fraction of the focal length. For example, if you had a 500 mm lens with a fixed f/8 aperture, the aperture is actually 62.5 mm. How much light is gathered during an exposure depends not just on aperture but also on shutter speed. And the response of the film to that light will depend on the sensitivity (speed) of the film, which is said to be such-and-such ASA (or ISO).
It is customary for the aperture to be varied in increments that correspond to a two-fold change in area. These increments are called f-stops, and a two-fold change in shutter speed or film speed may be referred to as a one f-stop change because it can be compensated for by a one f-stop change in the aperture, or vice versa.
Any serious photographer will be aware of the “Sunny 16” rule, which was used to estimate the proper camera settings before cameras were able to meter available light and automatically set the shutter speed and/or aperture in response. This says that for sunny conditions (LV15), if your shutter speed is the reciprocal of the ASA, the aperture should be f/16. If we can make a lens with a maximum aperture of f/4 (comparable to the Petzval lens of 1840), that’s 4 stops from f/16, so you can get 1/16 sec with full sun illumination and a ASA1 film. And for less luminous scenes, you can adjust the required camera settings or film speed accordingly.
In the additive system of photographic exposure (APEX), the appropriately weighted base 2 logarithms of aperture, exposure time, and film speed are combined into a single exposure value (EV) on the same logarithmic scale as the LV, so if the two are equal, there should be a perfect exposure (Focal3d 5).
Seeing in the Light: Silver
Prior to the digital camera, light was sensed by its ability to cause a chemical reaction on the part of a photosensitive chemical that, directly or indirectly, resulted in a color change and thus an image corresponding in some way to the imaged scene.
In the standard twentieth-century process, this photosensitive chemical was a silver halide salt, The halides of photographic interest were chloride, bromide, and iodide. Other photosensitive chemicals are known and are discussed later under the rubric of “alternative photographic processes.” However, they require much longer exposures, or artificial lighting, to ultimately produce a visible image, and are typically used in printing from film rather than for direct capture.
For ease of use, the silver halide salt was suspended in a coating medium, and this so-called “emulsion” is applied to a substrate (metal or glass plates originally, later paper or plastic) which is cut into sheets or rolls. I will generally use the term “film” to refer to the photographic material, whatever the actual substrate.
It is worth noting that film and photographic paper have much in common. Film is used inside the camera to capture the image formed by the camera from the scene itself. Photographic paper in turn is used nowadays to make copies of an image captured on developed film. However, in early photography, paper was also used as an original substrate.
The silver halide is present in the emulsion in the form of small (0.2-2 microns) crystals. (These particles are sometimes referred to as “grains,” but shouldn’t be confused with the grains that are seen with a loupe when a print is examined; those are 10-30 microns (Vitale).) When light strikes the crystal, light photons energize electrons to jump from halide ions into the conduction band of the crystal. The electrons subsequently combine with interstitial silver ions (more reactive than the silver ions that are in their proper place in the crystal lattice) to form metallic silver.
With normal light levels and exposures, the sensitivity of the film is insufficient to form enough silver metal to produce a perceptible image. However, as few as four silver metal atoms in a crystal could act as a seed for catalyzing the conversion of all of the silver in the crystal into silver metal (Duffin 172). So, the initial exposure to light creates a “latent image” formed of the crystals which contain “developable” specks of silver. Then one exposes the film to a “developer,” a chemical that selectively reduces the remaining silver ions in those crystals that contain these specks, thus creating the perceptible image in the form of black metallic silver. (We thus amplify four silver metal atoms to 109 or 1010 such atoms.) Next, we add a “fixer,” a chemical that removes the remaining unreacted grains. And finally we wash away the excess reagents and let the film dry.
The light sensitivity of the silver halides is as follows: chloride < bromide < iodide (Bancroft). Note that the intrinsic sensitivity of film is dependent not only on the halide mix, but also on the shape and size of the halide crystals (larger=faster) and the presence of any sensitizers. And the effective sensitivity is dependent on the developer composition and the development process parameters.
Silver halides are unstable. The film that came through the Ring of Fire will have an expiration date of two years from manufacture (longer if refrigerated). But that doesn’t mean that they are unusable after 1633. Some rolls of consumer color film shot 25 years after expiration still gave reasonable results, and others were heavily fogged and color-shifted. (Schneider). It’s luck of the draw!
Silver Halide Preparation
How will silver halides be made in the new timeline?
Silver chloride: Silver nitrate (lunar caustic) is already known to the alchemists; it is obtained by reacting silver metal with nitric acid (aqua fortis). Silver nitrate in turn reacts with sodium chloride to make silver chloride (“lunar cornea”) and sodium nitrate. The reaction was known prior to the Ring of Fire; it was published by George Claromontanus of Jena (1623) and attributed to the apocryphal Basilius Valentinus. In addition, natural silver chloride (chlorargyrite, horn silver) is “found in the upper levels of the silver lodes in Freiberg (Saxony) and in other silver mines,” and was first described (1565) by Fabricius (EderHP 24).
Silver bromide: Silver bromide is a rare mineral (bromargyrite) that occurs mainly in Mexico and Chile (Wikipedia); it is associated with evaporite deposits in arid regions. It has been found in Germany (Mindat) but I have found no evidence that it occurs in mineable deposits there. The easiest method of making silver bromide is by the reaction of an alkali (potassium or sodium) bromide with silver nitrate. To make this bromide, or an intermediate one such as iron bromide, you ultimately need bromine. “Bromine was originally isolated from seawater (1826), in which it occurs as bromides in concentrations of just 65 ppm (EA). In 1911, the principal commercial source was the salt deposits at Stassfurt, Germany; the salt is a mixture of potassium, sodium, and magnesium bromide (EB11) (Cooper, GG25).
Silver iodide: We have the same problems with the silver iodide mineral (iodargyrite). So, to make silver iodide, we ultimately need iodine. “Some seaweeds concentrate it—Laminaria is up to 0.45% iodine. Not surprisingly, seaweeds were the first commercial source of iodine. . . . Originally, the big producers were Normandy and Scotland. . . . Finally, iodides can be found in brine wells, although I am not sure whether this is the case in Europe” (Cooper, GG25). In April, 1634, Sharon Nichols had iodine, but not enough for the operation of Ruy Sanchez. Flint and Dennis, 1634: The Galileo Affair, Chapter 39.
The bottom line is that silver chloride should be available soon after the Ring of Fire—say, after the up-timers establish relations with Jena—but that acquiring silver bromide and iodide would take quite a bit longer as there is no established trade in either bromine or iodine, the sources are some distance away, and someone must be persuaded to extract them from seaweed or brine. It is unfortunate that the halide that is first available is the one that is least sensitive.
The Collodion Silver Process
This was invented in 1851, and it used collodion as the coating medium. The dominant form was the so-called “wet plate” process. A soluble iodide or bromide was dissolved in collodion (described below).
In canon, Sebastian Jones’ grandfather was an ACW reenactor who used historically correct wet-plate photography, and his grandmother, who is still alive in 1635, is also a wet plate photographer (Offord, GG46).
In the process used by American Civil War photographers like Matthew Brady (Wikipedia), the glass plate was coated with the collodion, which formed a viscous film, and then the plate was immersed in a solution of silver nitrate. The silver iodide or bromide formed in situ. Once the emulsion was formed on the plate, the photograph had to be taken and the image developed and fixed before the emulsion dried out—say, within twenty minutes. This necessitated a portable darkroom.
A few modern photographers make use of the collodion wet plate process for creative effect, and they report that the sensitized collodion has an effective speed of ASA 0.5-1 (KEH).
In general, modern wet plate photographers buy collodion rather than making it from scratch. But in the NTL, someone will need to figure out how to make it. “Collodion is a viscous fluid made by dissolving guncotton [nitrocellulose, pyroxylin] . . . in a mixture of alcohol and ether” (EB11/Collodion). The proportions needed for photographic use are given in EB11/Photography (5 grains nitrocellulose in one ounce of mixture of equal parts alcohol and ether).
The guncotton itself is made by reacting cellulose with concentrated nitric acid, and “comparatively slight variations in the concentration and temperature of the acids used produce considerable differences in the products” (EB11/Guncotton; cp. Cooper, GG29). In canon, nitrocellulose is commercially available from Brennerei und Chemiefabrik Schwarza at least as early as May, 1634 (Prem, GG47).
Dry plates. Attempts were made to develop a silver collodion plate that would retain sensitivity even when dry but these were unsuccessful (Focal 108). EB11/Photography (488) asserts that the method of Taupenot, using a bath of silver nitrate acidified with acetic acid, was “perfectly effective,” but don’t be fooled. While they were practical to make, and the plates could be stored for several weeks, they had only one-sixth the sensitivity of the normal wet plates (Kukulski).
While not available in Grantville literature, it appears that it is possible to instead put the plate in a “bath of 3.3% preservative solution of tannic acid for a few minutes,” and then let it dry. This version (Russell) is supposed to have a shelf life of over a year. However, the sensitivity is still one-quarter to one-sixth that of wet plate (Olphant). Von Monckhoven (Ch. XII) says that the exposure averages “one to three minutes on a favourable day.” This can perhaps be improved on by use of Draper’s modification of the normal development (immersing the plates after exposure in a vessel of hot distilled water) (Towler Ch. XXXVII).
The Gelatin Silver Process
In 1871, Maddox emulsified the silver salts in gelatin rather than collodion. Refinements were made and by 1911, a gelatin emulsion could produce from a 1/15th second exposure an image that with collodion required ten seconds (EB11/Photography 491). Elsewhere (492) it is said that on a bright day, with an aperture of f/16, the exposure should not be more than 1/4 second (implying that 1911 film was ASA4). In 1890, the “instantaneous” dry gelatin plates were about sixty times more sensitive than a wet collodion plate (EderHP 450), and EB15 agrees. (It is hard to reconcile these statements with the reported speed of collodion in modern wet plate photography.)
The OTL Kodak Brownie #2 Model F (post-1924) had a fixed shutter speed of 1/50 second and a meniscus lens with a wide-open maximum relative aperture of f/11 (Solomon). Using the “Sunny 16” rule, that implies a film speed of ASA 25. Here are the reported speeds of some famous B&W films: Super-X (1935) ASA 16; Super-XX (1938) ASA 50, Tri-X (1955) ASA 200. Bear in mind that there is a tradeoff between film speed and resolution.
It is a mistake to think of gelatin as just a means for suspending the silver salt particles. It influences the light sensitivity of the film in several ways and also helps stabilize the latent image and inhibit fogging during the development process. Gelatin eclipsed other coating media because of these special properties (Duffin).
EB11/Gelatin describes it as “the substance that passes into solution when ‘collagen,’ the ground substance of bone, cartilage and white fibrous tissue, is treated with boiling water or dilute acids.” (Yes, the horse sent to “the glue factory” is likely to become part of someone’s photographic film.) It goes on to describe presentation of “bone-gelatin” by treating the bones with hydrochloric or phosphoric acid, washing off the acid with water, bleaching with sulfur dioxide, and then steaming up to 85oC. Other sources indicate that the bones were from pigs and cattle (Peres 48).
We are also told that “skin-gelatin” is manufactured in the same way as skin-glue. EB11/Glue clarifies that parings and cuttings of sheep and ox hides are steeped in lime water to remove any attached flesh and blood. Presumably this was followed by acid treatment.
There is also a description of how to make “vegetable gelatin” (now called agar-agar) from seaweed. It was occasionally used as a substitute for bovine gelatin (Peres 38).
Nowadays, acid-extracted gelatin is called type A and alkaline (lime)-extracted is type B. Photographic gelatin is primarily type B (GMIA 19). While in EB11, the lime treatment is directed at hides, it in fact can also be used with bone. The green bone is cleaned and crushed and treated with dilute HCl to remove mineral salts, yielding ossein. The ossein is then limed (typically for longer than hides), washed with cold water to remove the excess lime, pH adjusted with acid, and the soluble gelatin extracted with hot water.
Chemically speaking, gelatin is a heterogeneous mixture of fragments of the protein collagen. These fragments vary in molecular weight from 15,000 to 400,000D (GMIA 6) and of course they also vary in amino acid composition around the collagen average. Since gelatin is obtained from natural sources, there will be source- and process-dependent variations both in the chemical makeup of the gelatin, and in the nature and proportions of impurities. The impurities include nucleic acids, amino acids, sugars, and sulfur-containing substances.
Some of these impurities are advantageous; the sulfur-containing substances, probably derived from the amino acid cysteine during the liming process, are known to increase the sensitivity of the silver salts. Modern practice is to use highly purified gelatin and achieve this sensitization by deliberate introduction of a thiosulfate (Focal3d 265), which can be formed by treating the gelatin with sulfur dioxide (Not available in Grantville literature: Duffin 36). Gelatin’s aldehydes, sugars, and sulfites are also known to be “chemical” sensitizers. On the other hand, gelatin contains the amino acids methionine and cysteine, which retard silver halide crystal growth (Focal3d 264).
There is no doubt that gelatin can be made early in the new timeline—it was first produced commercially in the Netherlands circa 1685 (GMIA 3). And with the slow, colorblind emulsions of the late nineteenth century, the contemporary food gelatin was adequate. However, modern photographic grade gelatin is much purer than modern food grade gelatin (Osterman), to afford better control over speed and spectral sensitivity.
Gelatin Emulsion Composition and Preparation
There is only limited guidance on emulsion composition, other than that it contains gelatin and silver halide. First, it is much less common for twentieth-century photographers to make their own photographic emulsions than to do their own developing. Second, the compositions of commercial photographic gelatin emulsions (and papers) were generally kept secret. So, even if we weren’t limited to Grantville literature for guidance, we would have to make some guesses.
Fortunately, EB11 dates to a time when there were still photographers alive who made their own gelatin emulsions. It gives one formula (5 grains potassium iodide, 135 grains potassium bromide, 175 grains silver nitrate, and 230 grains gelatin). However, from there we are on our own.
Until 1864, most emulsion contained silver iodide as the photosensitive agent (EB11/Photography 490). But iodide is now a more minor player. Grantville literature teaches that positive (slide) photographic emulsions usually contain a mixture of chloride and bromide, and negative emulsions are iodobromides—primarily bromide, but with a “small quantity” of iodide (Focal3d). Sources not available in Grantville may state a range: 1-8% (Duffin 18) or “order of 5%” (Allen 245).
EB15 teaches that one mixes silver nitrate with a solution of alkali halide in gelatin, and that this causes the precipitation of silver halide as fine crystals. No mixing particulars are provided. EB11 describes forming the halide, silver nitrate, and gelatin solutions in separate flasks placed in water at 150oF, combining the silver nitrate and gelatin, and then adding (1) half the potassium bromide drop-by-drop, and then (2) the potassium iodide and the remainder of the bromide the same way. Focal teaches two methods. In the “single jet,” the halide and the gelatin are in the vessel, and the silver salt is added by the jet. In the “double jet,” the gelatin is in the vessel, and the halide and the silver salt are added through separate jets. Focal3d (264) notes that the slower the addition, the larger (thus more sensitive) the crystals.
EB15 does not mention ripening. In 1878, it was discovered that if the hot gelatin were held for a sufficient time at a constant temperature, the film speed was increased (Focal 8). (This is the result of crystal growth.) It was this ripening that increased the sensitivity of silver gelatin plates to the point that they became attractive to professional photographers in the late 1870s. EB11 teaches placing a flask containing the emulsion in boiling water for 45 minutes, which I suspect would have resulted in ripening. Focal (263) refers to ripening the emulsion for 10-60 minutes at 40-70oC, with continuous agitation. In general, the higher the temperature and the longer the ripening period, the larger the crystals formed. However, there is much room for experimentation as to the effect of ripening time and temperature on sensitivity. And bear in mind there is such a thing as an emulsion being too sensitive, and fogging.
EB15 says that the gelatin is chilled and then remelted, but not why. Basically, the precipitation reaction also forms soluble potassium nitrate. The “classical” method of removing this (and other soluble impurities that might impair performance) is to add some dry gelatin, cool to about 40oF, shred the gelatin into threads (noodles) (this increases the surface area), and then wash in water (Focal3d 264). EB11’s quaint method of “noodling” is to place the cooled emulsion into a bag made of mosquito netting, and squeeze it, thus extruding the noodles through the holes. The noodles are then washed for several hours in cold water.
Sensitizers can be added to the gelatin. The terminology is confusing; a “chemical” sensitizer makes the silver halide more sensitive to the wavelengths of light to which it is naturally sensitive, whereas an “optical” (spectral) sensitizer causes it to become sensitive to additional wavelengths. I will address spectral sensitizers in a later section. Focal3d (48, 265) identifies four types of chemical sensitizers: sulfur compounds (like thiosulfate), reducing agents (like stannous salts), gold salts (ammonium auric thiocyanate), and polyethylene oxide. The gold salts are useful only in conjunction with the sulfur sensitizer. The emulsion is heated (“after-ripened”) for minutes to hours in the presence of the chemical sensitizer.
Focal also notes that a variety of additional agents may be added during finishing, including stabilizers, antifoggants, and hardeners.
The final step is coating the film base. According to EB11, gelatin noodles are warmed to about 120oF, and the resulting liquid is poured over glass plates. This of course had to be done under red safety lights (or no light once panchromatic films were available). Modern practice uses coating machines, but there is a thick veil of secrecy over the coating process.
Gelatin dry plates were available for purchase in the nineteenth century, but Nicol complained in 1879 that “the plate of no two makers are alike, and that hardly any two batches of any one maker are identical in quality.” We can expect that NTL plates are likewise variable in sensitivity and color.
Film Substrates (Bases)
The first substrates were glass (and occasionally metal). The advantages of glass were that it was flat, transparent and unreactive with the emulsion and developer chemistry; the disadvantages, it was rigid, heavy and fragile.
Bear in mind that as of the Ring of Fire, the only clear glass was the relatively expensive Venetian cristallo, and that glass was blown not cast, and therefore not exactly flat. (Cooper, GG5). But canon suggests that there will be considerable improvement in glass clarity and flatness by June 1634 (Cooper, GG13).
In 1879, gelatin dry plates were available in one-quarter size (3.125 x 4.125 inches) at three to four shillings per dozen (Wheeler 189). By 1890, the price had dropped (probably) to one or two shillings (cp. Hannavy 468).
Nitrocellulose had been used previously in manufacturing xylonite and celluloid, early semisynthetic plastics. In 1881, one photographer obtained sheet samples but found them too yellow and too uneven in surface for use as a glass substitute in collotypes and also too thick for dry-plate films. In 1884, Carbutt found a celluloid manufacturer who had developed both “a method of producing thick, clear blocks of celluloid and, secondly, a slicing mechanism that could cut sheets of celluloid of uniform thickness as thin as one-hundredth of an inch.” In 1888, he put on the market a “flexible celluloid film” (Harding). However, this was intended for use in sheet form; it was too thick to be rolled.
In 1888, Eastman introduced roll film with a paper substrate. A problem with paper was that it was opaque, and even waxing just made it translucent (Focal 108). During processing at the laboratory, gelatin was separated from the paper and applied to a transparent support.
By 1889, Eastman’s researcher had developed a transparent nitrocellulose film that could be rolled. In 1890, it was priced at four shillings for twenty-four exposures for 3 1/4 inches wide format to one pound and five shillings for twenty four exposures at 8×10 inches(!) (Harding).
Early nitrate film (1889-1903) had a film base that was less than 8 mils thick and, because it was coated with gelatin on only one side, tended to curl. The thickness was later increased in professional film to 8 mils, and both sides coated with gelatin, to keep the film flat (NPS M:2). It was sold in both sheet and roll form.
Unfortunately, nitrocellulose is highly flammable. (The concentration of cellulose nitrate was 10.5% in collodion emulsions, 12% in flexible film base, and 12.5% in weapons-grade guncotton (NPS M:1).) It also emits toxic gases and gives off heat as it deteriorates.
Consequently, it was gradually (1925-50) superseded by “safety film”: cellulose diacetate (1908-50), cellulose acetate proprionate (1924-45), cellulose acetate butyrate (1935-present), and cellulose triacetate (1934-present) (NEDCC; Vitale). The diacetate was easier to solubilize, but more brittle and less stable, than the triacetate.
Cellulose acetate was first synthesized in 1865. Cellulose triacetate is made by reacting cellulose with acetic anhydride (cp. MI 6) in the presence of sulfuric acid as both catalyst and solvent (CCD 182). From the 1950s, polyethylene terephthalate (PET) was used as a film base.
I previously predicted that cellulose acetate might first become available in 1632-4 and PET in 1635-7 (Cooper, GG29). For film in canon, see the end of this part.
Spectral (“Optical”) Sensitizers
The ideal photosensitive agent would have high but equal sensitivity across the visible light spectrum, and (unless needed for scientific purposes) no sensitivity to ultraviolet or infrared radiation. Unfortunately, the silver halides depart greatly from this ideal. Silver chloride is sensitive mainly to ultraviolet and violet light. In 1782, Senelier found that violet rays blackened silver chloride in fifteen seconds to the same extent that red rays did in twenty minutes (EB11/Photography).
Silver bromide, and more so, iodide, impart the ability to also absorb some blue light. (Duffin 99). Lea reported that with three dark green filters, silver bromide with a fifteen-minute exposure was the same as the iodide with 2.5. And with three red filters, there was no discernible change in the bromide paper after four hours exposure to bright sunshine on snow, whereas iodide paper gave a faint image after thirty minutes and a full one after four hours.
This color-blindness problem is acknowledged in canon (Offord, GG50): “any new photographic emulsions would need special dyes, which Lettie’s friend, Celeste Frost, an up-time trained chemist, was currently working on, to make any new film anything like equally sensitive to most of the colors of the spectrum.”
In order to achieve sensitivity across the visible spectrum, we need to add a substance that 1) absorbs light of lower energies, and 2) transfers the energy to the silver halide so as to initiate the photochemical reaction. If the film is sensitized to the entire visible light spectrum it is called panchromatic; if it can “see” greens and yellows but not reds, it is “orthochromatic.”
The possibility of spectral sensitization with a dye was discovered serendipitously by Vogel in 1873 (Sussman 10; EB11/Photography 496; Hentschel 248). Focal2d (1349) (but not 3d) identifies the dye coralline as sensitizing silver bromide to green rays so, if that is in Grantville, we have that as a starting point. In the 1870s, there were in fact two corallines, red (peonine) and yellow (aurine). Both were obtained by heating oxalic acid, phenol, and sulfuric acid, but formation of the red dye required a higher temperature (EB9/Carbolic Acid). MI112 gives three syntheses for aurine, all using phenol as a starting material (MI112). Unfortunately, I believe it to be a weak sensitizer as it was never used commercially.
Aurine is a triphenylmethane dye, and I previously predicted that the first dyes of this type could be available as early as 1633. None of the other triphenylmethane dyes is identified in Grantville literature as a sensitizer, but they might be made for use as dyes. These dyes include malachite green (EB11/triphenylmethane; MI639, discovered 1877) which proved useful as a red sensitizer (Duchochois 512) even on silver gelatin (Bothamley).
Klein’s recommended red sensitizer is ethyl violet (53), and I believe this is the one used in autochrome (1907) emulsions. Ethyl violet is a triphenylmethane dye but unfortunately even that information is not available in Grantville literature. According to Bancroft (323), methyl (gentian, crystal) violet (CCD 585, MI 485, formula only, discovered 1861) and fuchsine (MI 472; the second basic dye, discovered in 1858), if tested, may be found to be yellow sensitizers, but have “only a very slight effect on a silver bromide gelatine whereas they are very effective in making a silver bromide collodion plate sensitive to the yellow.” On the other hand, Yoshida (1918) found methyl violet to be an acceptable red sensitizer for the photographic plate.
Once Vogel’s finding was accepted, there was an active search for additional sensitizers. Unfortunately, this was a matter of trial and error, the effect being dependent not only on the structure of the dye but also on the type of silver halide used, the type of emulsion (collodion vs. gelatin), and the dye concentration (Hentschel 250). The optimum concentration is one that coats the silver halide crystals with a monomolecular layer of dye and once this is exceeded the sensitization falls off rapidly (Seliger 136).
EB11 mentions that “eosin” was one of the dyes experimented on, without stating its color of sensitization. Eosine in fact may have been the first dye found to have a sensitization effect on silver gelatin. But “for a good sensitizing effect, the dye must be very pure and used only in dilute solution.” Hence, eosine-sensitized dry plates weren’t readily available until 1882 (Hentschel 252).
Eosine (CCD349) is obtained by bromination of fluorescein. Fluorescein (CCD395) is derived by heating resorcinol (CCD 759) with phthalic anhydride (CCD 692). Resorcinol is obtainable by fusing m-benzenedisulfonic acid with excess sodium hydroxide. Benzene sulfonic acid is made by reacting benzene (a coal tar constituent) with fuming sulfuric acid (MI128). The synthesis of the disulfonated benzene is not described in Grantville literature, but it appears that with sufficient excess of fuming sulfuric acid it would be obtainable, although there are a lot of byproducts that must be removed (USP3097235). Phthalic anhydride is also a problem; it is made preferably by oxidation of napththalene or ortho-xylene with oxygen over a special catalyst (10% vanadium pentoxide plus 20-30% potassium sulfate) (CCD 692; M&B908). A perhaps more accessible method involves oxidizing naphthalene with a mixture of mercuric and cupric sulfate in presence of sulfuric acid (MI826).
Erythrosine was found to be superior to eosine with respect to greens and yellows, and Focal3d (743) says it was the first sensitizer used commercially (Focal2d doesn’t mention it at all). Erythrosine (CCD352) is the sodium or potassium salt of iodeosin, which is derived from the interaction of fluorescein and iodine in the presence of iodic acid. A related sensitizer is Rose Bengal (MI 922), derived from resorcinol and tetrachlorophthalic acid.
Taking into account the number of different chemicals that needed to be isolated or synthesized, I would grade eosine and its relatives as being just as difficult a target as NTL chloramphenicol. Chloramphenicol took something like two years to make, and it was a government-sponsored high priority target. In contrast, research into photographic chemistry appears to have been started later and conducted by individuals relying on their own resources. So I am iffy as to whether eosine-type sensitizers would be available by 1636.
One interesting option is chlorophyll, which can be extracted from green leaves with alcohol. If you were to happen on its entry in CCD (206), you would find it identified as a “sensitizer for color film.” It is also listed as a red sensitizer in Focal2d (but not 3d!). So how well does it work? Klein (23) (not available in Grantville literature) reports “it sensitizes collodion emulsion for red, and is a good but very unreliable, sensitizer.” He warns that “an excess greatly decreases the speed of the plate” (52-3). Eder (41) (not available in Grantville literature) says the sensitivity to red is one-fifth to one-tenth that to violet. Reportedly, Becquerel (1874) and Ives used it, but it “gave satisfactory results mainly in the wet collodion process; with gelatine emulsion plates it was far less useful” (PT 138). Du Hauron (1874) sensitized a bromide collodion plate with coralline and chlorophyll (EderHP 645).
Methines are dyes in which two heterocyclic nuclei are connected by a chain consisting of an odd number of methine (CH) groups (Hampel 360). Hampel (997) and Focal3d (743) disclose that the modern spectral sensitizers are almost all “polymethines,” in which the methines are connected by alternating double and single bonds. The term “cyanine” (also mentioned by Focal2d) is a subclass in which the heterocyclic nuclei are quinolines (CCD 249). The nuclei of a polymethine dye could also be benzooxazoles, benzothiazoles (CCD690), benzoselanazole, and beta-napthothiozole (Hampel).
The term “cyanine” refers not only to a chemical class, but also to a specific compound known as quinoline blue, and prepared (although this information isn’t available in Grantville) in 1856 from the ethiodides of quinoline and lepidine (Hamer 34). It was shown to be a sensitizer in 1875, but was considered “somewhat unreliable” (Hewitt 74) and eclipsed by the isocyanines (1900-1920s), the merocyanines (1930s), and other sensitizers (Hampel 997).
Homocol is an isocyanine (Newton), and EB11 states that a plate stained with homocol is “sensitive throughout the visible spectrum.” Unfortunately, neither CCD nor MI give the chemical structure of homocol.
The original cyanines were monomethines, and the methine connected the 4 and 4′ positions in the quinolines. The isocyanines had a connection between the 2 and 4′ positions. It was discovered that if the methine connection in isocyanines was polymethine, the greater the length of the polymethine chain, the “redder” the sensitization, and a chain of up to 11 methines was useful.
The first panchromatic gelatin plates (1906) were based on the isocyanines pinacyanol and pinachrome (Hentschel 252), but this wouldn’t be known in Grantville. One could, however, search exhaustively through MI and CCD, looking for chemicals with the cyanine skeleton, and eventually find Pinacyanol (quinaldine blue) (MI901), a trimethine, and hope that it is a sensitizer (it is). But no synthetic route is given.
It appears that it was synthesized in our timeline by heating an alcoholic solution of quinaldine ethiodide in the presence of alkali and formaldehyde (Hamer 13; Mills). The quinadline ethiodide is a quaternary salt and it is obtained by heating a mixture of equimolar amounts of the alkyl iodide and quinaldine (Lund); an obvious expedient. Quinaldine (2-methylquinoline) occurs in coal tar (although isolating it would be a chore) and may be synthesized by heating aniline and paraldehyde with HCl (CCD 747). I have not been able to find out how its ethiodide salt is prepared.
I am a bit dubious about this all being carried out in the 1630s. No one in Grantville had a masters, let alone a doctorate, in chemistry. The introductory organic chemistry textbooks are unlikely to provide any guidance. M&B has a few pages on the synthesis of quinolines but nothing on their reactivity. Even one of my heterocyclic chemistry texts (Gilchrist) devotes just two pages to cyanine dyes, and eight to the general features of quinoline and isoquinoline chemistry.
A further problem in the development of panchromatic media is that when dyes are combined, they can interact unfavorably, as in fact happens with pinacyanol and pinachrome (Power), and cyanine and eosine (von Hubl 96). On the other hand, sometimes a second substance can supercharge a sensitizer (Hampel 998).
Based on the foregoing, I think that wet plate collodion photography may be able to compete in 1636 with silver gelatin because we can make panchromatic collodion emulsions with coralline (or fuchsine) and chlorophyll, whereas the spectral sensitivity of gelatin emulsions will be restricted until an appropriate isocyanine is synthesized and characterized.
Because the light only creates a latent image in the silver emulsion, we need a developer. The development time and temperature is chosen so the silver in the crystals with developable specks is reduced to the point of creating a perceptible image with proper tonality (not under- or over-exposed). The developer also reduces the silver in crystals that lack the developable specks (i.e., are not part of the latent image), producing fogging, but at normal development temperatures the latent image-catalyzed process is a million times faster. Development is halted by a stop bath in acetic acid (vinegar).
We must identify the chemicals used as developers, and determine how to synthesize them. Fortunately, there is far more information in Grantville literature on developers than on spectral sensitizers!
We begin by considering which developers are mentioned in general encyclopedias rather than books that just darkroom users might own. From EB11/Photography, we find ferrous oxalate (quickly abandoned), pyrogallic acid, hydroquinone, Eikinogen, Metol, Amidol, and Ortol (the latter a trademark for a developer whose chemical identity is not in Grantville literature).
Pyrogallol (pyrogallic acid) is obtained by heating gallic acid with water (CCD 743, MI894). Gallic acid (MI 480) in turn may be prepared by hydrolyzing the tannins from nutgalls.
Hydroquinone may be derived from aniline by several different routes (M&B 976, CCD 457, MI547). There is also a natural source of hydroquinone but it requires a bit more digging to find it in Grantville literature. Arbutin (MI 98) is a glycoside found in blueberry, cranberry, cowberry, bearberry and pear tree leaves; it is easily hydrolyzed by dilute acid to yield glucose and hydroquinone.
Metol (methyl-para-aminophenol sulfate) is from hydroquinone and methylamine (CCD565, EB15).
Amidol (2,-4-diaminophenol HCl) can be made from chlorobenzene (M&B 813) and other starting materials (MI 338).
Eikonogen (1-amino-2-naphthol-7-sulfonate, sodium) has a known chemical structure (MI 58), and the immediate reaction yielding it is given, but it will take some doing to work backward to a starting material available in the 1632 universe, and I doubt it worth the trouble.
Phenidone (1-phenyl-3-pyrazolidinone) is mentioned by Sussman and in Ilford formularies. It is much more potent than metol (Wikipedia). It may be synthesized from phenylhydrazine and beta-chloropropionic acid (MI 819). These are several steps removed from the available starting materials, and hence I don’t think this will be available in the early 1630s.
Rodinal (p-aminophenol) was the first product sold by Agfa and is cited by Sussman. It can be prepared by reduction of p-nitrophenol with iron filings and HCl (MI58, CCD47). P-nitrophenol is obtained by nitrating phenol and separating the para and ortho products by distillation (MI751). Phenol is a coal tar ingredient.
Catechol (pyrocatechol) is mentioned by Ilford (Mitchell 196); it is of interest because it can be isolated from a natural source, the catechin residue of the boiled juice of Acacia catechu. It can also be obtained by hydroxylation of salicylaldehyde (related to aspirin, Dr. G take note!) with hydrogen peroxide (MI894).
I previously predicted that amidol, hydroquinone, Metol, phenidone, catechol, pyrogallol, and Rodinal, being characterized by isolated aromatic rings, would first be available in 1634 (Cooper, GG27), but if film is being sold in 1633, then some developer was available back then.
Focal lists hydroquinone, chloro-hydroquinone (adurol), catechol, pyrogallol, para-aminophenol (Rodinal), amidol, metol, glycin, para-phenylene-diamine, L-ascorbic acid, and phenidone. It is extremely common to use metol and hydroquinone in combination.
It’s not so described in Grantville literature, but acetanilide was an experimental developer in the nineteenth century (Wikipedia). I find it interesting because it is one of the precursors of chloramphenicol, and thus has already been made by NTL 1633. Unfortunately, I cannot say how good a developer it was.
Bear in mind that the actual developer solution does not contain just the developer per se, but also additional substances, such as an activator, a restrainer (to prevent fogging), and perhaps a preservative (EB15/Photography, Technology of). The formularies give complete recipes, but generally do not explain the purpose of each ingredient.
EB11/Photography gives one complete formula, based on pyrogallol. It is implied that the activator is alkaline, and the formulation contains ammonia. EB15 also identifies sodium carbonate as an activator, and EA adds borax and sodium hydroxide. EA also suggests potassium bromide as a restrainer.
Sodium thiosulfate (“hypo,” hyposulfite of soda) is suggested by EB11/Photography. Interestingly, it also is used as a cyanide antidote. According to EA, the fixer will also include an acid (acetic acid) , a preservative, a buffer (boric acid), and possibly a hardener (potassium alum).
The ability to amplify the effect of the light by development is a huge advantage of silver halide-based photography. However, silver halide has the disadvantage that the effect of the light is to cause the film to darken, not lighten, and thus the image is the inverse of the scene (which is why we speak of film negatives).
In early photography, an apparent reversal (of the negative) was achieved in ambrotypes and tintypes. In the ambrotype, a black background was provided by viewing the glass plate by reflected light against black velvet, or using a plate made of a dark red glass or coated with a black varnish. The exposed areas, while dark, would reflect more light than the background and thus appear light. The tintype (ferrotype) was similar in concept, but the emulsion was coated on a metal (preferably iron) plate that had previously been enameled in black. Tintypes were made from both collodion and gelatin negatives. For both ambrotypes and tintypes, the negative ideally was underexposed (thus lighter, and requiring shorter exposures), This led to the use of potassium cyanide as the fixer.
But a true reversal is possible. Conventionally, the negative image can be converted to a positive one (with tonalities matching the scene) by projecting light through the negative and onto a silver halide-sensitized photographic material. The unexposed areas on the film will fully transmit the light and thus will turn the material black, and the fully exposed areas will block the light, leaving the material white. (For the availability of high-intensity light sources in the 1632 universe, see Cooper, GG67-71.)
Alternatively, the image can be reversed by chemical means. In the daguerrotype, silver iodide was generated in situ by reacting a silver plate with iodine vapors. Exposure to light created a latent image. The image was developed by mercury vapors that adhered only to the affected areas, creating a mercury-silver amalgam that was white in color. The silver iodide was removed with hypo and the unexposed areas were polished silver and would be dark if held to reflect a dark surface. However, while the daguerrotype created a positive image, it was not possible to produce copies.
In modern black and white photography, after development and before fixation, we add a bleach that reduces the metallic silver and thus destroys the latent image. We then expose the film to light long enough to create developable specks in the crystals that didn’t evolve them originally. We then develop these specks and fix the resulting positive image (Spottiswoode 237).
Nineteenth-century photographic plates were substantially larger than the frames of late twentieth-century consumer film. A “full plate” tintype was 6.5×8.5 inches, and larger glass plates and gelatin sheet films have been sold. In contrast, 35 mm roll film has 24x36mm frames, and Minox “spy” cameras used an 8×11 mm frame.
In canon, Schmucker and Schwentzel “have a camera that can take bigger photographs” than a 10×12 plate. (Offord, GG46).
The larger the format, the less enlargement is needed to achieve a particular print size, and that reduces the apparent graininess of the print. But larger format cameras are heavier and more awkward to operate.
Silver-Based Photographic Printmaking
A disadvantage of the daguerrotype was that it couldn’t be reproduced, which limited the revenue that a professional photographer could make from a single exposure. In contrast, the negative produced by the silver collodion and silver gelatin processes can be used as a “master” from which numerous positive prints are made.
In essence, the photosensitive emulsion is coated on paper, and this is exposed to white light through the negative. Since a silver-based emulsion inverts tones, producing a negative, treating a photographic negative as a “subject” inverts it, so we get a positive print. To shorten the required exposure time, a strong artificial light source can be used.
If the paper is placed in direct contact with the negative, we get a contact print, which is the same size as the negative. (This is another reason that early “film” was quite large.) Enlargements could be made by using a diverging lens to spread the light across a larger surface; naturally, a strong light source was needed.
Normally, prints weren’t made directly from slides (positives). Rather, you first made an intermediate negative (internegative) and then made the print from that (Sussman 490). However, the Cibachrome process provides a direct positive color print from a color slide (488).
Both “printing-out” papers (POP) and “developing out” papers (DOP) are known. POP are photosensitive papers used at one time by professional portrait photographers to make proof copies. They did not require development, but the exposures were on the order of five to thirty minutes (Sussman 386). The paper was not fixed and so would darken completely in a week or two if exposed to room light. This was deliberate, so clients couldn’t just keep the proofs and not order the final prints. In contrast, DOP papers were intended to receive shorter exposures and then undergo development.
Papermaking is of course a well-established industry among the down-timers. Optical brighteners are used to increase the whiteness of modern papers, but this is not essential. Photographic papers, prior to sensitization, are normally coated with either baryta or resin. This protects the emulsion from any chemicals in the paper.
“Baryta” refers to the mineral barite (barium sulfite) but is actually a mixture of barium and strontium sulfate. Barite is known to alchemists in the form of the phosphorescent “Bologna stone,” discovered in 1603. (The phosphorescence was the result of a copper impurity so don’t use it as an identifying feature.) (Inglis-Adell).
The “resin” coat was not a natural resin, but rather a pigmented polyethylene. However, new timeline paper chemists could experiment with other natural and artificial polymers. The main virtue of resin-coated paper is that it’s waterproof, making it easy to rinse and dry (Benson 172).
The earliest photographic prints did not use an “emulsion.” Rather, Talbot (1839) merely soaked the paper in a common salt solution and then brushed one side of it with a silver salt (he used nitrate) solution. This is termed “salted paper.”
It was superseded by papers in which the silver was formed by the reaction of alkali halide and silver nitrate in albumen (egg white). The process is described in detail by EB11/Photography. This “albumen silver emulsion” was at one time (1847) used to make the original negatives, but it was superseded by “collodion silver emulsion,” which was more sensitive—silver albumen required a five- to fifteen-minute exposure (Gustavson 28). Nonetheless, it survived as a print-making medium. In fact, “the albumen process produced far more prints than all of the other chemical printing methods of photography’s early years combined” (Benson 110). Albumen prints were usually toned with gold chloride before fixation; this inhibited yellowing and made the image more permanent.
Besides albumen silver prints, we may of course also make collodion or gelatin silver prints.
Grantville literature should reveal that printing papers are identified as chloride, chlorobromide, and bromide papers (Sussman 387), and that these range from slow to fast, respectively. (For that matter, any photographer who did his or her own printing would know this.) In general chloride papers were used just to make contact prints, and bromide papers just to make enlarging prints (their high sensitivity compensating for the inverse square reduction in light intensity as a result of projection from the enlarger). Sussman says they are a hundred times as fast as chloride papers (keep this in mind if we are forced to use chloride alone for a while in film, too). Chlorobromide papers could be used for either contact printing or enlargement.
It is sobering to note that the estimated speed of enlarging paper is about ISO 3, and of contact paper, only 1-10% of that (Focal 586).
Modern papers were made in several contrast grades (soft, medium, hard), with the abnormal grades used to expand or contract the tonal range of the negative. I doubt that Grantville literature will explain how this was achieved.
Papers can be given a matte, semi-matte, or glossy finish, but I think the details belong more to an article on papermaking.
There are plenty of photosensitive chemicals, the problem is in finding ones that are sensitive enough to produce a useful image in a reasonable time. For example, the iron-based papers have about one-millionth the light sensitivity of silver-gelatin enlarging papers (Ware). The silver process, because of the possibility of amplification by development, is really the only one fast enough to capture action, and is also more suitable for portraiture (people can stay still only so long). However, other processes can be useful for making prints from negatives or slides since one can then use a strong actinic (ultraviolet and blue) light source, and the film used for masking the photosensitive print paper isn’t moving (and doesn’t mind staying still). Sunlight is 10% ultraviolet, and I have already mentioned artificial light sources.
It should be noted that all of these non-silver print methods are contact print methods (you need a negative or positive the same size as the desired print); if the light were projected by an enlarger it would be too weak to be of practical value. One expert writes, “The closest I have come to making a non-silver print through enlargement was by putting a black-and-white negative in a slide projector about 12 inches from paper sensitized with vandyke solution. After 40 minutes a faint image printed out” (Van Heuren 18). In contrast, a Vandyke contact print using direct sunlight can take just 3-5 minutes (Raso).
EB11/Photography (497-8) provides a long list of substances tested for photosensitivity, including salts of gold, platinum, mercury, iron, copper, manganese, lead, nickel, and tin.
Cyanotype. Paper is sensitized with a mixture of ferric ammonium citrate and potassium ferricyanide. Where exposed to light, the ferric ion is reduced to ferrous, and reacts with the potassium ferricyanide to form the pigment Prussian blue (EB15/Blueprint). The first photographic use was by Atkins (1843), who made contact prints of photographs of algae (Crawford 68). Cyanotype is slow; figure a 30-minute contact exposure with a 275W sunlamp at 15 inches (164).
The chemistry was used by the 1870s to make “blueprint” copies of engineering drawings; the drawing was made on translucent paper and used as a mask for the sensitized paper. Thus, the black lines on the drawing became white lines in the blue print. In the engineering use, the background was dark blue, but the chemistry is “capable of beautiful tonal scale.” and “many thousands of amateur photographs” were contact printed as “cyanotypes” (Benson 136).
Platinotype. In 1880, Willis published a process using a solution of ferric oxalate and potassium chloroplatinate to sensitize paper. Exposure to UV light (for about five minutes in good sunlight) produces a “faint brownish image.” However, when developed with warm potassium oxalate, this “almost immediately” creates an image. Light first reduces the ferric (iron) to ferrous, and then this reduces the platinum of the chloroplatinate to platinum metal. Platinotype prints were much more stable than silver-based prints. Platinum paper was widely used until WW I, when it was recognized as a strategic metal. In 1916, Willis introduced a parallel process using palladium (Benson 138; Stulik; Ware). Platinotypes are merely mentioned in EB15, so hopefully there’s a Focal Encyclopedia in Grantville. A typical contact exposure is twenty-five minutes with a sunlamp, eight with a carbon-arc, and one with direct summer sun (Crawford 170).
Anthotype. Herschel (1842) sought to use acidified alcohol extracts of flower petal pigments as a photosensitive material. Unlike silver salts, they form positive images, because they are bleached by sunlight. The most sensitive plants reportedly include “blueberries, raspberries, strawberries, pokeberries, beets, turmeric, Yellow Japonica, Iris, Red Poppies, spinach, Marigold, Double Purple Groundsel, Red Dahlia, and most blue flowers” (James 142).
While they require extravagantly long exposures (hours to weeks) and must be stored in the dark (lest they fade), I was intrigued by the following tidbit: In early eighteenth-century France, there was a tradition of securing stencils on fruit, then exposing them to sunlight. “The sunlight would bleach, or ripen, the areas of the fruit’s skin into decorative patterns that were, I suspect, employed to make a table display more impressive” (143). I can imagine them, or similarly treated flowers or leaves, being put to similar use in the new timeline. Or perhaps some religious charlatan would find it helpful to have some words of praise for himself appear on vegetation.
Film Speed and Sensitometry
Early gelatin dry plates from different manufacturers, and different grades from the same manufacturer, varied in light sensitivity, and the prudent photographer tested a sample plate. An 1884 study showed a 20-fold variation in sensitivity among fifteen commercial plates, all developed using the same developer (Pickering). Effective film sensitivity would of course depend not just on the emulsion, but also on the development process.
The speed of film can be crudely estimated by photographing a subject at various shutter speeds or apertures, determining which setting resulted in a proper exposure, and applying the “Sunny 16” rule. However, it is better to have a more reproducible system. Grantville literature offers limited guidance.
The degree to which a film darkens in response to light follows an S-curve, with a long straight section in which the post-exposure density (logarithm of opacity) is linearly proportional to the logarithm of the exposure. The slope of that section is a simple measure of the speed (the actual ASA definition is more complicated).
To determine that slope, we need to vary the exposure in a precise fashion and measure the change in film density. We can’t do this by changing the intensity of the light because that will also change its color, and film is more sensitive to some colors than others. So we need to use a constant intensity light source and a precisely graduated filter.
EB11 describes the commercial Warnerke sensitometer (1878). For a sensitometer to give meaningful results, there must be an easily reproducible set of light exposures. Warnerke placed the plate in contact for thirty seconds with “phosphorescent tablet . . . which was previously excited by burning one inch of magnesium ribbon in front of it.”And for the latter, Warnerke used a transparent “density plate” with 25 squares of varying density. From sources not available in Grantville, I know that the phosphorescent tablet was calcium sulfide (Hannavy 1264) and Warnerke’s “density plate” was a “screen of different thicknesses of colored gelatin” (Vogel).
EB11 also doesn’t mention the complaints. For example, that “fields 19-16 showed very little gradation in the transparency, and then there was a sudden jump.” The brightness of the tablet decreased during the critical half minute (Vogel). And finally that the blue phosphorescence, while a good match for unsensitized plates, was less so for orthochromatic ones (Schumann).
Instead of Warnerke’s plate, one could use a wedge of glass, as in a wedge photometer (EB11/Photometry), so there is a continuous linear variation in thickness and therefore exponentially in transmission. This would need to be used in conjunction with a density scale on which you would find the shade of gray matching the gray at a particular position on the exposed film. Goldberg figured out (1910) how to cast a gelatin wedge of neutral color (Buckland 57).
Hurter and Driffield (1890) took a different approach, using a “standard candle at one meter distance” and varying the duration of the exposure on different parts of the test plate. They then measure the opacities with a “special photometer” (EB11). No particulars are given as to the construction of the “standard candle” or the “special photometer.”
Exposure Calculators and Meters
The “Sunny 16” rule is an imperfect basis for rating film speed because “full sun” can actually vary in intensity with latitude, time of year, and time of day. Moreover, the variation is not just in intensity but also in the spectral distribution, and thus the results will be different for unsensitized, orthochromatic, and panchromatic films.
The first exposure table (1840) detailed exposure times depending on the weather and the length of the day. As cameras evolved to give photographers a choice of apertures and shutter speeds, linear and circular slide rules were developed so you could input the light value, film speed and aperture and read off the required exposure time. However, the light value was extracted from a table, or a graph taking into account time of day and season (Lord).
The actinometer (1884) was a chemical exposure meter; it was a photosensitive paper exposed to the light falling on the subject until it darkened sufficiently to match a reference tone. You timed how long this took and then calculated (possibly with a slide rule) the proper exposure for film of a given speed with given camera settings (Focal3d 289).
With an extinction meter (1887), you viewed the scene through a graduated neutral density filter at a numerical scale for a set viewing time and noted which reference number could be read. Note that this is measuring light reflected off the subject rather than incident light. Preferably, part of the visual field is unfiltered so the eye doesn’t compensate for the reduced light level. Extinction meters were still for sale in the 1950s.
The first photoelectric exposure meter (1930s) used a selenium photocell (Focal3d 290). The current varies depending on the light striking the photocell and is read off with a galvanometer. A selenium photo-resistor amplifier appears in canon in October, 1633 (Huff, GG36). My best guess is that the selenium was obtained as a byproduct of the electrorefining of copper, cp. Carroll, GG50.
Cadmium sulfide photocells (1960s) are about 200 times more sensitive than selenium cells and made through-the-lens metering possible. The principal cadmium ore is greenockite (cadmium sulfide), and it is associated with calamine (and may have been used by the ancient Greeks as a yellow pigment). In the early nineteenth century, “Stromeyer, the inspector of pharmacies, investigated a complaint by Hannover druggists that the zinc oxide they made by heating calamine sometimes was yellow rather than white (Emsley 76). The calamine trade is centuries old, and I can’t help but wonder whether this yellow adulterant is known to the seventeenth-century apothecaries.” (Cooper, GG25).
Artificial light sources can be used to project a slide (positive) so it can be viewed by an audience, to illuminate a scene so it can be photographed, or in printing (the light passing through a negative of positive to expose underlying photographic paper).
Display projection. Several pre-Ring of Fire writers suggested shining light from a candle or oil lamp through an illustrated paper in order to project an image onto a screen or wall. However, the first true “magic lantern”—with a concave mirror to concentrate the light on the slide and a lens to project it—was made (but not publicly demonstrated) by Huygens (1659). The magic lantern was commercialized by Walgenstein (1662) (EderHP 46ff). The first lantern slides were hand-drawn, but photographic slides were projected by 1846 (340).
Film and Paper Exposure. Any light source of sufficient intensity (remember the inverse square law) could be used for display projection, but for action on film or paper, you generally want one rich in ultraviolet radiation (actinic), as without spectral sensitizers (see below), silver emulsions only respond to light in the ultraviolet to blue-green range.
The lime light was briefly used in 1841 as portrait lighting but thereafter was only used for slide projection and printing. The electric carbon arc light, powered by batteries, was used for scene illumination from 1840 on, notably to photograph the Paris catacombs (1861). A night studio with a dynamo was set up in 1879. You may use carbon arc but you need good ventilation (carbon monoxide is released) (EderHP 528ff).
The first truly portable “flash” was a lamp burning a magnesium ribbon or powder (1864). Flash powder was a mixture of magnesium and various oxidants (e.g., potassium chlorate) (1887). Burning magnesium produced actinic light, but at best the process generated lots of smoke, and at worst it could explode. Flash bulbs were a related technology; a current was run through a magnesium filament inside a glass bulb with an oxygen atmosphere.
If prolonged lighting is needed, mercury vapor lamps will eventually be a possibility. Low pressure mercury vapor lamps appeared in 1901 and high pressure ones in 1936.
I previously provided information on artificial light sources in the context of life at sea (Cooper, GG67-71).
Contact Print Frame
At its simplest, this has a glass plate and a wood or metal back. The negative and contact print paper are placed inside and clamped together, and the paper is exposed through the glass plate and the negative. A split (hinged) back design allows the printer to check the progress of exposure without disturbing the registration (Focal3d 654).
Enlargers provide a projection assembly (comprising an illumination system, a source film holder, and a mechanism for adjusting their elevation) and a base to which the projection assembly is attached. The enlarging paper holder is attached to the base. The film and paper must be held flat and parallel to each other. The illumination system comprises a light source and either a condenser lens or a diffuser.
Condenser lens design aims at providing a flat, distortion-free field with a short “subject”-lens distance.
Photography in Canon
The first use of photography is in Flint, 1632; ID photos are taken of captured mercenaries. Later stories also use photos for identification purposes (Offord, GG39). From identification, it is not much of a jump to using it to record forensic evidence (Richardson, GG26, Howard, GG59, Hasseler, GG50, Carrico, Ring of Fire IV and, inadvertently, Offord, GG45). One camera is used for military reconnaissance (Flint, 1634: The Baltic War, Chapter 36), and another for an aerial (kite) farm survey (Offord, GG31). There are references to photojournalism (Offord, GG46) and portrait photography (Prem, GG51), too.
“Film” in Canon
Unfortunately, the canon on new timeline (NTL) film is rather muddled. As of July, 1633, Lettie Sebastian in Grantville is “working on making new film,” as well as using “wet plate” media. (Offord, GG50, Offord, The Chronicles of Dr. Gribbleflotz, Chapter 13). The “new film,” by implication, will be a dry (gelatin) medium. They started work in May, 1633 (Offord, private communication).
In April, 1634, Dr. Phillip Gribbleflotz becomes interested in Kirlian photography. He finds that Lettie and the chemist Celeste Frost have made photographic chemicals, and perhaps also film, but would need guidance to scale up production (Offord, GG17).
From the above, it appears that in April, 1634, there is no commercial sale of NTL photographic film yet known to Dr. Gribbleflotz or his contacts. Moreover, in July, 1634, in Grantville, Olivia Villareal (who taught photography for a while) tells William Oughtred that she hears “they’re about ready to start making” film again (Carroll & Wild, GG36), implying that it hadn’t been done previously. However, it is possible that she doesn’t consider glass plates to be film. So earlier manufacture of gelatin silver-coated glass plates is a possibility.
In August, 1634, a would-be mail order bride has her photograph taken. The exposure is taken using a “double dark” inside a “flat wooden cassette.” The implication is that the film is a coated glass plate. The film is processed in a nearby photographer’s tent, so it might be wet plate collodion, but dry plate gelatin is more likely (Offord, GG24).
In Flint and Cooper, 1636: The China Venture (expected to be published in late 2019), Judith Leyster will join the USE mission to China as an artist-photographer. She uses gelatin silver glass plates, manufactured by Brennerei und Chemiefabrik Schwarza, in slow, moderate and fast sensitivity grades. These plates must have been available before September, 1634, when the USE mission left Europe.
By December, 1635, black and white film and photographic chemicals are being produced by HDG (Offord, GG37). However, they were probably produced several months earlier, indeed before July, 1635. In that month, the equipment received at Race Track City outside Vienna includes “a movie projector for the new down-time-made celluloid movies” (Flint, Goodlett, & Huff, 1636: The Viennese Waltz, Chapter 25). There is also a reference to a celluloid factory in Russia in April, 1634 (Flint, Goodlett, & Huff, 1636: The Kremlin Games, Chapter 48) and to people in Grantville converting videotapes into “celluloid movies” in September, 1634 (Flint, Goodlett, & Huff, The Barbie Consortium, Chapter 28). In fact, celluloid is used to make magnetic tape by January, 1633 (Id., Chapter 19).
Originally, “celluloid” meant film made from cellulose nitrate. Kerryn Offord was of the opinion that BCS would have considered and rejected cellulose nitrate given that it is no easier to make than cellulose acetate but is substantially more hazardous. But either someone was making it, or the term “celluloid” was being treated as synonymous with movie film. (Merriam-Webster online lists both meanings.)
A feature film (“On His Majesty’s Secret Service”) is shown in Magdeburg in November, 1635. The author of the story (Offord, GG28) advises that his intent was that it used cellulose acetate stock, but the story doesn’t make that explicit.
What we are sure of is that by May, 1636, Brennerei und Chemiefabrik Schwarza is manufacturing gelatin silver-coated cellulose acetate and using it to make sheet and roll film (Offord, Gribbleflotz, Chapter 21). In fact, Offord envisions (private communication) that mass production of cellulose acetate sheet and roll film will begin much earlier, in late 1634 to early 1635 in Hamburg, after pulp starts arriving from Arendal. He suggests that small quantities of the cellulose acetate film even might be available in August, 1634.
However, according to another thread in canon, by October, 1633, a villager has “bought his son Johan a camera, in spite of the fact that Johan couldn’t develop the picture himself” (Huff, GG36). This village was “about one hundred and twenty miles northeast of Grantville as the crow, or the radio wave, flies. Almost due north of Dresden in Saxony.” (Huff & Goodlett, GG9).
In early spring 1635, during the run-up to the battle of Zwenkau, Johan declares, “I’m getting my Brownie.” This, presumably, is the camera that was purchased in 1633. We are told that it “used chemically-treated paper on a roll. Twenty-four exposures per roll and then you sent the roll back to the factory to be developed. And they sent you the pictures. The camera cost twenty-five dollars, the rolls two dollars each and the developing ten dollars a roll.” (Huff & Goodlett, GG36). Since OTL Brownies are collectors’ items, and paper film obsolete, these presumably are NTL manufactures.
But how would a villager 120 miles from Grantville hear that cameras and film are available for purchase in October, 1633, without Lettie Sebastian, Celeste Frost, Dr. Gribbleflotz and his associates, and Olivia Villareal knowing about it even by 1634? Chances are that if such a villager knows about it, it was advertised by radio and in the Wish Book. Moreover, who formulated the film? In October, 1633, it could not have been Celeste or Dr. Girbbleflotz.
One suggestion that was made on Baen’s Bar was that the camera bought in 1633 was an inexpensive up-time camera, such as an Instamatic, and the NTL Brownie was purchased later. But I am doubtful that any up-time camera would be inexpensive (it would have value just as a relic of the OTL future), and given the reference to developing, it was bought with intent to use, and thus having ascertained that there is compatible up-time film for it and that someone can process it. Moreover, an Instamatic or similar camera would probably have come with a color print film, and it is doubtful that any one in Grantville would have the chemicals for developing it (C-41 process for the Instamatic 126 film). And if those conditions were met, why would the person subsequently downgrade to an NTL brownie?
While there is no perfect resolution, my recommendation is that “bought the camera” just means made a down payment, with the balance due when the camera and more importantly film and processing become available. And that the film and processing weren’t available until late 1634, consistent with the other canon. In any event, by November, 1635 there are “box-brownies” in Southamptonshire, England, ordered from a catalogue (Dingwall, GG43).
In future parts I will discuss color photography and camera design.