A Stain Worth a Thousand Words

Sometime in the middle-to-late 1700s, an unknown individual in England purchased a book titled New Practical Improvements and Observations on Some of the Experiments and Considerations Touching Colours (1738). We don’t know who this person was or what their background was: it could have been any of the “Gentlemen and Ladies that amuse themselves with Painting in Water Colours” to which the author, John Hoofnail, addressed the book. It might have been John Stuart (1713–1792), Marquess of Bute, and from 1760 to 1763, Prime Minister of Great Britain, as this copy, now owned by the Othmer Library, eventually found itself in his library. Alternatively, any person with a spare shilling—then worth half a skilled tradesman’s daily wages—could have purchased the book.

While we don’t know much about the person who used this book, we can assume that they had a great interest in the chemistry of color: the chemicals and chemical processes that create dyes and pigments. The pages of this book are covered in hand-drawn pointed fingers, or “manicules,” that the owner likely used to mark interesting or important sections. These drawings mark instructions for making pigments, as well as Hoofnail’s own insights into the impact that specific ingredients had on the final characteristics of a pigment. The anonymous user was not just interested in reading about colors, though. The numerous stained pages suggest that they likely used this book as a guide to making colors themselves.

An example of pages marked with manicules, from New Practical Improvements and Observations on Some of the Experiments and Considerations Touching Colours.
Science History Institute

By far, the deepest and most vibrant staining appears on page 19. Streaks of bright magenta stain the bottom of the page; this same color appears again, though covering a smaller area, on page 64.

It’s striking to compare this intense color to the far more muted stains littering other pages of the text in green, blue, and yellow. How could it be possible that the magenta stain is so vibrant, at least 200 years after it was first made, when all the other stains in the book have faded?

While it’s impossible to be certain of the source of this color without chemical testing, all lines of evidence point to one culprit: cochineal. In 1738, when Hoofnail published this book, basically every painter or dyer in England—or indeed, much of the rest of the world—knew about American cochineal, a dye that comes from the bodies of tiny insects. Ever since Spanish colonizers began to export the dye from their American territories, they controlled an ever-increasing share of the global market in red dyes and paints.

It isn’t hard to understand why so many artisans switched to the new Spanish red. These artisans already had access to other sources of red dye; they could turn to the roots of madder plants, brazilwood extracted from the woods of specific trees, or even closely related insect species, like kermes or Eurasian cochineals. However, American cochineal was far more concentrated than Eurasian cochineals or kermes, produced a brighter red than madder, and had a more long-lasting dye than brazilwoods.

Even as European artists rapidly incorporated American cochineal in their palettes, they often struggled to control its characteristics. They quickly noticed that American cochineal tended to have a blueish hue, unlike the sources of red they were used to. Although opinions were hardly universal, there was a common belief among Europeans in the 17th and 18th centuries that orange-hued scarlet was more desirable than blue-hued crimson. How, then, would they achieve their desired scarlet?

One possible solution would be to ask the Indigenous people of the Americas that had been using cochineal to paint books and dye textiles in many hues for centuries, if not millennia. Indeed, some clues come from natural historian and physician Francisco Hernández. From 1571 to 1577, Hernández traveled throughout Mexico to collect Indigenous knowledge about plants and animals, including cochineal. Although the massive 16-volume treatise he wrote was never published in its entirety, translations of his descriptions of cochineal appeared in 17th-century works published in Latin, Spanish, Dutch, French, and eventually, English. Yet this widespread description of cochineal provided little obvious instruction.

Hernández noted that red, scarlet, and purple colors can be achieved with cochineal, depending on the manner of preparation. He even noted that “a particularly exquisite color” could be obtained if cochineal was combined with alum and a native plant called tezhoatl. Yet European readers had no access to this plant, as it was not one of the products regularly exported from the Americas. Hernández also provided no instructions regarding the proportions of ingredients or the sequence in which they were added. Thus, European readers were unable to convert his descriptions into recipes that they could understand.

Lacking access to Indigenous knowledge, European artists relied on their nations’ chemists to uncover the principles that predicted cochineal’s qualities. In England, one of the most important figures to contribute to this effort was the famed scholar Robert Boyle. In his 1664 book Experiments and Considerations Touching Colours, Boyle explored how colorants like cochineal yielded different colors according to their concentration and the presence of metals and acid salts. Although he noted that cochineal could be used to dye scarlet with a tin vessel, the lack of detailed instructions made this knowledge difficult for artisans to implement. By contrast, although Hoofnail’s book was far shorter, it contained more in-depth descriptions of his experiments with cochineal, providing instructions that non-chemists could use to make their own cochineal paints.

Like other Europeans before him, Hoofnail struggled to obtain scarlet paints from cochineal. To convert water-soluble cochineal dye into water-insoluble pigment, one must first precipitate dye molecules onto an inorganic metal salt. The resulting product, known as a “lake pigment,” could then be suspended in oil or water to be used as a paint. The most common choice of metal salt for Europeans and Indigenous Americans alike was alum (Kal(SO₄)₂, also commonly used as a mordant to fix dyes to textiles. Alum on its own, however, could not produce a scarlet pigment from cochineal, as Hoofnail noted.

What color did cochineal-alum precipitate make? Color descriptions are often subjective, making it difficult to say. According to Hoofnail, it was crimson. According to 16th century Friar Bernadino de Sahagún, it was purple; according to his Nahuatl-speaking Indigenous Mexican collaborators, it was the color of a sweet potato—perhaps purple, pink, brown, or orange. It was disagreements like these that eventually led to the creation of the sample book genre. Sample books, which included dyed or painted samples alongside color names, descriptions, and/or recipes, allowed dyers to compile their knowledge, dye manufactures to advertise to consumers, and color chemists to establish an agreed-upon set of terms. Unfortunately, the cochineal recipes in these 19th-century books tend to be far more complicated, incorporating cream of tartar, tin, alcohol, and even dangerous chemicals like nitric and hydrochloric acids. Thus, they provide little insight into the color of cochineal-alum precipitate.

Luckily, modern-day dyers and colorists can help bridge the gap between historical color descriptions and recipes and our own conceptions of what those colors are. In my conversations with master dyer and weaver Ignacio Netzahualcoyotl, I learned that his art studio uses cochineal and alum to dye their wool magenta.

I’ve also done some of my own experimental recreation of cochineal lake pigment recipes. Using cochineal, alum, and a close relative of tezhoatl, I was able to make a similar colored precipitate.

Finally, the Science History Institute is currently hosting a special exhibit, Artists Transform the Sample Book, which includes an artist’s book made from paper and linen thread dyed pink with cochineal. According to artist Jennifer Rosner, this dyeing was achieved with an alum mordant.

Dye Experiments by Jennifer Rosner, from the Institute’s Artists Transform the Sample Book exhibition.
Courtesy of Jennifer Rosner

With all this in mind, it seems likely that the magenta stain found in the Othmer Library’s copy of Hoofnail’s New Practical Improvements and Observations on Some of the Experiments and Considerations Touching Colours is the product of a cochineal-alum solution. The user of this book may have been following Hoofnail’s simple recipe for a “crimson” tincture made from cochineal and alum. Alternatively, they may have been following Hoofnail’s other recipes using cochineal but spilled their experiment before adding the salt of tartar or madder necessary to shift the “crimson” to “scarlet.” The book’s user was clearly interested in the wide range of recipes in which cochineal could be used—approximately one third of all bookmarks appear next to cochineal-focused text.

I can’t help but wonder what this person thought when they stained their book magenta. Perhaps they were embarrassed to have made a mess or frustrated that they had spilled their costly cochineal. Alternatively, maybe they were proud to have physical evidence of their experiments. Regardless of how they felt, I’m glad that the spill happened. Sometimes, the most interesting discoveries happen not from the words on the page of a historic book, but from the material evidence of how that book was used.

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