True Blue: Blue Pigments and Dyes in the 1632 Universe

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Blue pigments and dyes are rare in nature and consequently blue colorants are precious commodities in the pre-RoF world. Some are minerals, some are plant or animal extracts, and a few are synthetic in nature.

A colorant must be incorporatable into the intended substrate, and it should be resistant to environmental conditions (light, heat, water, acids, alkalis) that might degrade or remove it. And of course it should be nontoxic, easy to produce in quantity, and inexpensive.

Bear in mind that nowadays colorants are incorporated not only into textile fibers, but also woods, stones, rubbers, plastics, glasses, ceramics, foods, cosmetics, pharmaceuticals, hair and skin, biological specimens (as microbial and histological stains), and coatings (including inks and paints). Artists are only a very small segment of the modern market.

I see the effect of the RoF as two-fold: (1) encouraging the application of the experimental method to systematic improvement of the methods of producing the existing colorants; (2) making down-timers aware of colorants not previously known to them and giving at least some information as to how to produce them.

In my Industrial Alchemy series, I assumed that Grantville literature included the various general encyclopedias (including the 11th (EB11) and 15th (EB15) editions of the Encyclopedia Britannica), the Chemical Rubber Company (CRC) Handbook, the Merck Index (MI), the Condensed Chemical Dictionary (CCD), two introductory organic chemistry texts (Morrison and Boyd (M&B), and Solomon (S)), a descriptive inorganic chemistry text (unspecified), and Cotton and Wilkinson's Advanced Inorganic Chemistry. It also includes various field guides to North American minerals and plants.

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PIGMENTS

 

Pigments are "colored, black, white, or fluorescent particulate organic or inorganic solids which usually are insoluble in . . . the vehicle or substrate into which they are incorporated. . . . Pigments retain a crystal or particulate structure throughout the coloration process" (SDC).

Some dyes may be converted into pigments by precipitating them with a metallic salt; the precipitate is called a lake pigment. There is, for example, an indigo lake.

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Natural Copper Blues (Azurite)

 

Azurite is a blue mineral, a copper carbonate with two hydroxyl (OH) groups, thus having the formula Cu3(CO3)2(OH)2. (The green mineral malachite is also a copper carbonate, but with only one hydroxyl group.) EB11/Azurite gives a few of its physical characteristics: crystal system and luster, streak, hardness, and specific gravity. It arises by the weathering of copper by carbonated water and "thus is a common mineral in all copper mines." It has occasionally been worked as a copper ore; the mineral is 55% copper.

While lightfast, it can be dissolved by dilute acid, and if exposed to water (e.g., fresco painting), it turns green as a result of conversion to malachite.

It reportedly was first used in the Neolithic, at Catal Huyuk circa 6000 BCE (Scott 108). Azurite can be found in the Sinai and the Eastern Desert of Egypt, and some believe that the Egyptians made occasional use of it. However, a recent survey of artifacts from the Fifth Dynasty to the Roman period failed to find any use of azurite as a colorant (Nicholson 111).

"Azurite was used in wall paintings of the Song (960-1279) and Ming (1368-1644) dynasties," and in pre-Columbian America, it was used by the Indians of the American Southwest and the Classic period Maya (Scott 109).

It "was the most important blue pigment in Europe beginning in the Middle Ages, particularly from the fourteenth to the seventeenth century" (Scott 109). Over the eighteenth century, it was gradually displaced by Prussian blue.

According to Scott, "Germany was the principal supplier of azurite [to Europe] during the sixteenth century, with mines in Saxony [Goldberg], Tyrol [Schwartz] and Saarland [Wallerfangen]; the last source was known from Roman times" (Id.; brackets from Eastaugh 33). But Gettens says that Hungary was the main source until the mid-seventeenth century. Azurite is also found in Chessy (near Lyons, France), Sardinia, and Austria (Baker 25).

The process for converting it into a pigment is straightforward: break into small pieces, grind them dry down to a powder, then grind them some more in water ("levigation"), and finally dry out the particles.

Other natural "copper" blues exist, but most are rare minerals, and they may have been too green to be competitive. The most interesting is probably chalcanthite (hydrated copper sulfate) as "in arid climates it forms much larger deposits where it may become an important copper ore" (Eastaugh 97). Scott (146) says that "it was well known in antiquity as a mineral whose uses may have included pigment and medicinal preparations."

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Synthetic Copper Blues (especially Blue Verditer)

 

Lime Blue. "Artists' manuals from the Middle Ages onward provide recipes for making artificial copper blue pigments . . .." (Dackerman 60; Orna). One such recipe, from De Coloribus et Mixtionibus (late 11th century) says to make "azure" by adding lime [calcium oxide] and very strong vinegar [acetic acid] to a pure copper flask and bury it for a month. Some later recipes feature a different copper source (brass shavings, bronze, or verdigris). Others replace mineral lime with burnt eggshells, or vinegar with wine, and some featured sal ammoniac (ammonium chloride) as an additional ingredient (Krekel).

Krekel (not in Grantville literature, but a Grantville chemist could perform a similar systematic analysis of the down-time recipes) demonstrated that calcium oxide and elemental copper, in the presence of acetic acid, do react over a period of weeks to months to form reddish-blue crystals if the pH of the supernatant is 12.5-13. These crystals were identified by X-ray diffractometry (not available in Grantville) as CaCu(OH)4.H2O, which Krekel dubbed "lime blue." The acetate ion apparently acts as a catalyst, since if acetic acid is omitted the reaction doesn't occur, even though there is no acetate ion in the mineral. If ammonium chloride is also provided, then after a few days one obtains a blue-green compound equivalent to the mineral calumetite Cu(Cl, OH)2.H2O; in this situation vinegar is unnecessary.

Lime blue is formed immediately if calcium oxide is reacted with copper acetate. (Krekel didn't say, but I presume this would be obtained in situ by the combination of acetic acid and verdigris.) It proved to be a stable pigment in wall paintings and animal glue, but not in linseed oil.

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Blue verditer is a synthetic azurite (basic copper carbonate). It was used in the seventeenth century as a house paint (Gettens 31). It was also used in the illumination of the Coram Rege Rolls (1672) and in eighteenth-century oil paintings (Scott 114).

MacTaggart suggests that initially blue verditer was "something of an English specialty." An indication of how it was first made is its alternative name, "refiners' verditer." To separate gold from silver, nitric acid was added, dissolving the silver as silver nitrate. To then regain the silver, they poured the "silver water" over copper plates; the copper replaced the silver. Or, if the goal were to separate silver from copper, then they would add nitric acid, dissolving the copper as copper nitrate. Either way, the copper nitrate solution was added to chalk (calcium carbonate), which turned green ("verditer" is a corruption of vert de terre, "green of earth") and was essentially synthetic malachite. This appears to have been a way of turning the useless copper nitrate solution into a salable product.

Occasionally, a more valuable blue pigment was produced instead. Even in 1662, they could not "hit upon a more certain rule" to make the blue product (Ball 117). Sometimes, according to Robert Boyle, months went by without obtaining a single batch of blue verditer. This uncertainty affected price; there were three grades of "ashes," and they ranged in price from one to six shillings an ounce (Kirby 36).

MacTaggart's modern experiments (which are an example of the kind of contribution that Grantville can make) identified three factors that controlled the form of the precipitate: "the concentration of the copper nitrate solution, the temperature, and the frequency and vigour of the stirring." (The chalk concentration was not critical.) The more desirable blue verditer was obtained when 15g of cupric nitrate was dissolved in 200 ml distilled water, with the chalk stirred fairly vigorously at intervals of not more than half an hour, with a temperature not exceeding 12oC [54oF]. Mactaggart suggests that the seventeenth-century refiner's problem was that for much of the year, the day was too warm to make blue verditer.

In the late eighteenth century, Pelletier developed a more consistent synthesis that involved "mixing copper nitrate and lime, washing the green precipitate and mixing it, while wet, with quicklime . . .." (Eastaugh 56). In the nineteenth century, potash (potassium hydroxide) was poured into a copper sulfate solution, forming copper carbonate precipitate, which was ground with lime (calcium hydroxide) and a dash of sal ammoniac (ammonium chloride). An early twentieth-century recipe was "adding lime and potassium carbonate to copper sulfate, then treating the precipitate . . . with sal ammoniac and copper sulfate" (Scott 114-5).

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I also want to briefly mention copper sulfate pentahydrate (synthetic chalcanthite), known to the alchemists as blue vitriol. It is possible to grow large crystals of this chemical, and conceivably they could be ground into a pigment.

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Vivianite (Blue Ochre)

 

This was used occasionally as a pigment in Roman times, and in twelfth to nineteenth-century Europe—most notably in Vermeer's The Procuress (1656).

It is a hydrated iron (ferrous) phosphate (Fe3(PO3)2.8H2O). It forms white crystals that turn dark blue or blue-green on exposure to air (as a result of oxidation of the iron). The best-known deposits are those in the St. Agnes mine of Cornwall, England. In Germany, it is found in the limonite ores of Amberg-Auerbach and in the pegmatites of Hagendorf, Bavaria. It may also be found in peat bogs, clayey soil, and, ghoulishly, in the vicinity of skeletal remains (Wikipedia; Eastaugh 397; essentialvermeer.com; Siddall/Vivianite; Hrala; Master Pigments).

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Egyptian Blue

 

This is the first synthetic pigment! (While its chemistry is the same as that of the mineral cuprorivalite, that mineral is so rare that it wasn't discovered until modern times.) Moreover, Egyptian blue is "chemically completely stable in all media" and "absolutely lightfast."

It's known to have been first used before 3000 BCE, and it was the primary blue pigment of the Mediterranean world through Roman times. In medieval and Renaissance times, its use was rare (Riederer 27), being apparently superseded by ultramarine, azurite and smalt. However, Egyptian blue was been identified in a 1524 painting by Giovanni Battista Benvenuto (Bredal-Jørgensen; McGouat).

Vitruvius' De Architectura (Book VII, Chapter 11, section 1) provides some clues as to how it was manufactured: "Sand is ground with flowers of sulphur [elemental sulfur obtained by sublimation of brimstone], till the mixture is as fine as flour, to which coarse filings of Cyprian copper are added, so as to make a paste when moistened with water; this is rolled into balls with the hand, and dried. The balls are then put into an earthen vessel, and that is placed in a furnace. Thus the copper and sand heating together by the intensity of the fire, impart to each other their different qualities, and thereby acquire their blue colour."

While Vitruvius doesn't specifying adding any alkali, the alkali content of Egyptian blue was more than 1%, and sometimes as high as 4%. The alkali source could have been plant ash (potash, potassium carbonate) or natron (a natural mixture of sodium salts, primarily sodium carbonate decahydrate). The alkali serves as a flux (reduces the melting point of the mixture) and modern experimentation shows that sodium carbonate, potassium carbonate, and borax can all be used (colourlex.com).

Chemically, Egyptian blue is a calcium-copper tetrasilicate (assumed formula CaCuSi4O10), so Vitruvius' recipe is incomplete; it doesn't identify a calcium source. It is possible that it was an impurity in either the sand or the alkali source. The calcium compound could be a carbonate, sulfate, or hydroxide.

Although Vitruvius mentions Cyprian copper (which I assume is the pure metal), a copper alloy or salt (oxide, carbonate) could also be used.

There were no published recipes for Egyptian blue after the Roman era and before the eighteenth century (Riederer). However, Talier's Nuvo Plico (Venice, 1704) gave a recipe for "cerulean color" that was plainly based on Vitruvius (Gaetani).

Some (Davy, 1815, who found a pot of "pale blue colour" at Pompeii) have wanted to rediscover the ancient techniques of making Egyptian blue, and others (Deschamps 1893; Bock, 1916) just cared about the result; i.e., they wanted to "reintroduce Egyptian blue as a modern pigment." In the late twentieth century, systematic experiments—again, something Grantville's scientists will encourage!—explored the influence of the reaction time and temperature, the proportions and particle size of the reactants, and the reaction atmosphere (Riederer 32-4).

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Han (Chinese) Blue and Purple

 

These are also synthetic pigments. Their chemical formulae are BaCuSi4O10 and BaCuSi2O6, respectively, but two other barium copper silicates might also be present (Berke). The purple of Han purple is the combination of the dark blue of the nominal mineral and the red of copper oxide, which is a high temperature decomposition product of the barium copper silicate. While first discovered in Han dynasty wall paintings, they date back to the late Western Zhou (~800 BCE). Han blue was used until the end of the Han dynasty (220 AD).

Unfortunately, no ancient recipes for them have been found (Berke 97). The copper source could have been copper sulfide, malachite, or azurite. The silicate source could have been sand or quartzite. The barium salt could have been witherite (barium carbonate) or barite (barium sulfate). Barite is found in deposits throughout China. Berke believes that barite was the main starting material, but if so, lead salts (e.g., carbonate or oxide) must also have been added to serve as both catalyst and flux. The temperature would have to have been 950-1050o C (113).

Even if an ancient Chinese artifact colored with Han blue were presented to the up-timers, they presently lack the ability to identify the chemical nature of the pigment. At best they might be able to detect the presence of the barium, the copper, and the silicate. (Fitzhugh determined the exact stoichiometry by X-ray diffraction and saw that its pattern matched of the barium copper silicate synthesized by Pabsi (1969) and analyzed by Bayer (1975). I find it hard to believe that we will have these capabilities in the NTL soon enough to affect stories.)

However, writers are permitted some liberties, and perhaps one may hope that a recipe that did not survive into the OTL twentieth century is still in existence in the seventeenth century and is imparted to some visitor interested in Chinese chemical arts. That would then provide a starting point for systematic experimentation in Europe. (Or a Chinese artisan could be convinced by a visitor of the effectiveness of the experimental method and create improved Han blues.)

 

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Lapis Lazuli and Ultramarine

 

Lapis lazuli is a metamorphic rock derived from limestone that contains (25-40%) the chemically complex blue mineral lazurite. The blue of lazurite is attributable to trisulfide ions (Wikipedia) rather than to copper. Lapis lazuli was used decoratively by the ancient Egyptians (e.g., coffin of Tutankhamun) and Sumerians (carved statuettes, etc.). Cleopatra used ground lapis as an eyeshadow (Bowersox). The ancient Egyptians obtained it from Tefrer (probably Sippar) but most likely it was actually mined in Afghanistan (Montet 190). Most ancient lapis artifacts are found in Mesopotamia, closer to the source.

Prior to the nineteenth century, the only economically significant source were the mines of Badakshan (ancient Bactria), mentioned briefly in The Travels of Marco Polo (Book 1, Chapter 29). They lie in Hindu Kush, in-between Iskazr and Azarat, in the upper valley of the Kokcha (see Herrmann for detailed maps). Chances are you will not find those towns in the usual world atlas; on mine, you would have to say they are between Charikar (near Kabul) and Zebak (which lies on a tributary), or that they are upriver from Faizabad and Jurm. The mines are adits dug into the mountainside by lighting fires under the rock, throwing icy water on it to crack it, and then carrying away the fragments (Finlay 343).

The deposits near Lake Baikal in Siberia (not yet found in Grantville literature, and of poor quality—Herrmann) and in the Chilean Andes (near Ovalle, Chile, and a pale blue—EB15) were not worked until the nineteenth century (Plesters) and are not particularly accessible.

The Audubon Society Field Guide to North American Rocks and Minerals mentions the smaller deposits "on Italian Mountain in the Sawatch Mts. of Colorado, on Ontario Peak in the San Gabriel Mts., Los Angeles Co., and in Cascade Canyon in the San Bernadino Mts., San Bernardino Co., California." (cp. Rogers; Romirez). If exploited in the new timeline (wherein Japan, with Dutch assistance, has established colonies on the West Coast), it is most likely to be by the Japanese, or possibly the Dutch or Spanish.

Ultramarine. The rock could be ground into a powder, for use as a pigment called ultramarine. However, "unless the mineral is of very high quality, simple grinding and washing . . . produces only a pale grayish blue powder . . .. "Soon after 1200, an improved method of extraction came into use . . .. The principle of the method was that the ground mineral was incorporated into a mixture of melted wax, resins, and oils . . . and the molten mass, usually wrapped in a cloth, kneaded under a dilute solution of lye . . .. Blue particles of lazurite are washed out by this process and are collected by settling . . .. The effectiveness of the method probably depends on the preferential wetting of the blue particles . . .." (Plesters 38-9). The kneading process took several days (Finlay 322).

Nonetheless, a painter writes: "Even the finest natural ultramarine, ground assiduously by hand, is riddled with odd minerals: calcite, pyrite, augite, mica. These deposits cause the light to be refracted and transmitted in subtly different ways. No two strokes of paint are the same in their fundamental composition" (Mangli).

The first known use of the powder as a pigment was local, in the 700-900 AD cave paintings in temples close to the Sar-e-Sang mine (Holiday Pigments). The pigment came to be known in Europe as azurrum ultramarinum, abbreviated to "ultramarine;" this means "across the sea" and Europe imported it from Asia, by way of Venice. (Indeed, sometimes Venice imported the lapis rather than the pigment, and the Venetians ground it (Mozzato).) In Europe, it was used at least by the thirteenth century. In the sixteenth century it was more popular in Italy than in Spain or Northern Europe (Orna; Plesters 40).

I should note that there were actually several grades of ultramarine; "the best grade, with the largest particles and fewest impurities, separated out first; the last, containing much colourless material . . . was often known as ultramarine ash." Unfortunately, European sources generally do not specify the grade.

The remoteness of the mine and the laborious extraction process combined to make ultramarine about as expensive (at least in Europe) as gold. In 1508, Durer complained about paying 100 florins for a pound in Nurnberg (Finlay 318). "In 1626, 45 guilders were paid for an ounce of ultramarine for Ruben's Assumption of the Virgin. . . ." (Kirby 35) Consequently, artists required that their patrons supply it, or pay for it in advance, and contracts would specify exactly where it would be used. If blue was needed elsewhere, azurite would serve (even though it was greener than ultramarine). Azurite was also used as an underpaint to reduce the amount of ultramarine required.

There was of course the problem of fraud; suppliers who sold azurite-adulterated ultramarine, and for that matter artists who cheated their patrons by holding back some ultramarine.

Tests were developed to distinguish the two; if they are both heated, azurite turns black (copper oxide) when it cools whereas ultramarine doesn't (Eckstut 186). Note that while heating to redness is okay, if you make it white hot, "ultramarine tumesces and loses its blue color, leaving a yellowish white glassy mass of silica" (and probably a very contrite apprentice) (Plesters 44).

Azurite itself wasn't cheap (in 1471, azuro fino cost 1.25 ducats/pound in Venice, as compared to 6 for ground lapis lazuli in 1473 (Mozzato)), and it in turn might be replaced by smalt, blue verditer, or indigo (Kirby 36). Van Meegeren's forgery of a Vermeer was exposed by his inadvertent use of cobalt-adulterated ultramarine (Finlay 343).

The heat test also distinguishes some other blue pigments; Prussian blue turns orange-brown (ferric oxide), while indigo sublimes to a blue vapor. Smalt, cobalt blues, manganese blue, and phthalocyanine blues are heat-resistant, but may be distinguished from ultramarine by their resistance to concentrated hydrochloric acid (45).

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Synthetic Ultramarine

 

The first synthetic lapis finds were serendipitous. In 1787, Goethe discovered that the "blue deposits on the walls are lime kilns near Palermo . . . were cut and used locally as a substitute for lapis lazuli in decorative work." We do not know whether they were also ground for use as a pigment. In 1814, Tassaert found similar deposits in the soda kilns of the French royal glass factory and analysis revealed a composition similar to natural ultramarine. He suggested that synthesis of ultramarine was feasible (Plesters 55).

Synthetic ultramarine was invented, independently and almost simultaneously, by Guimet and Gmelin in the late 1820s. Guimet's ultramarine "sold for 400 francs per pound in Paris, the price of the natural pigment then being 3,000-5,000 francs per pound . . .." In 1955 the price ratio was 80:1 (53).

CCD merely says that it is derived by "heating a mixture of sulfur, clay, alkali, and a reducing agent at high temperatures." The gist of the Gmelin (1828) manufacturing process is disclosed in Grantville literature. One version involves "by fusing a mixture of soft clay [an iron-free kaolin, preferably 2 parts silica to one part alumina], [anhydrous] sodium sulphate, [powdered] charcoal, [anhydrous carbonate of] soda and sulfur [powder]. The product is first white but turns green when mixed with sulfur and heated. Once the sulfur fires, the mixture turns blue. You can obtain a blue product more rapidly by "heating a mixture of pure clay, very fine white sand, sulfur and charcoal in a muffle furnace." However, it may have a red tinge (EB11/Ultramarine).

A later encyclopedia description is to take "equal amounts of china clay, sulfur, and sodium carbonate, with lesser amounts of silica and rosin or pitch. The mixture is fired slowly to 750° C (1,380° F) and cooled in a sealed furnace" (EB15).


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About Iver P. Cooper

Iver P. Cooper, an intellectual property law attorney, lives in Arlington, Virginia with his wife and two children. Two cats and a chinchilla rule the household with iron paws. Iver has received legal writing awards from the American Patent Law Association, the U.S. Trademark Association, and the American Society of Composers, Authors and Publishers, and is the sole author of Biotechnology and the Law, now in its twenty-something edition. He has frequently contributed both fiction and nonfiction to The Grantville Gazette.

 

When not writing (or trying to get an “orange blob” off his chair so he can start writing), he has been known to teach swing dancing and folk dancing, or to compete in local photo club competitions. Iver adds, “I can’t get my wife to read my fiction, but she has no trouble cashing the checks.”

Iver’s story “The Chase” is in Ring of Fire II