Welcome back, everyone!
Since I finished my pigment maps last week, I am now returning to their write-ups for the final step in my reports: collecting historical recipes. In most cases, pigment recipes will change over time, due to factors like the depletion or discovery of materials or progress in science. The former requires manufacturers to adapt to the available materials while the latter can create new ways to make the pigments synthetically. For some pigments, like lead-tin yellow, synthetic production can increase their availability by providing an alternative for the otherwise limited natural supply. For others, like chrome yellow, the new processes are used to improve the pigment’s properties.
I came across one exception to this trend of multiple recipes of production when researching the manufacturing process for Indian yellow. I mentioned in a previous post that there are many synthetic pigments sold today under the name Indian yellow, but the true pigment that I studied was discontinued in 1921. Before its prohibition, Indian yellow had a relatively consistent preparation and I found few differences between sources.
(I’ll admit I’m also choosing to discuss this pigment in particular because of its unique production process.)
As the name may suggest, Indian yellow was primarily made in India. Farmers called Gwalas (milkmen) would raise cows on a diet consisting solely of mango leaves. Mango leaves contain euxanthone, which through the metabolic process of the cows would cause the conversion to salts. This was key to the creation of the pigment which was composed of calcium and magnesium salts of euxanthic acid. The gwalas would collect the urine of the cows in small earthen pots several times a day. Later, it would be concentrated by heating it over a fire, thus precipitating the pigment. Next, the liquid would be strained through a cloth and the remaining sediment was made into a ball. These balls were next dried over a charcoal fire, then in the sun. At the end of this process, the crude form of the pigment would be sold to merchants who would have to refine the pigment before it could be sold for artists’ use. This was done by making the crude balls into a powder, then washing it with boiling water and purifying it before redrying it for use as a base for water or oil colors.
The problem with this process — and the reason the pigment was later banned — is that a diet of only mango leaves is harmful to the cows. It would leave them undernourished and most could only produce pigment for two to four years. When these details were reported by T.N. Mukharji in 1883, they sparked an investigation that later led to the prohibition of the pigment’s manufacturing soon after.
I’m now coming to the end of my internship and senior project. Next week I will be working on the final reports, my research paper, deliverable, and presentation. Until then!