Is there cow urine in Van Gogh's famous work "Starry Night"?

When talking about Van Gogh's works, many people will think of the famous "Starry Night" or "Starry Night". This painting does look very romantic, but you may not expect that the bright yellow moon and stars in the sky in the painting actually contain cow urine.

Van Gogh's "Starry Night", Image source: Wikipedia

In fact, it is not just "Starry Sky". Many paintings use a pigment called "Indian Yellow", which is extracted from the urine of cows that have eaten mango leaves.

Magic Indian Yellow

The pigment Indian yellow may have originated in Persia. It was introduced to India in the 15th century and began to be used as a dye and painting pigment.

Because this paint is very bright and light, it works great for depicting bright yellow beaches, brown cliffs, boats, sunrises, and sunsets.

Moreover, Indian yellow can be mixed with green, orange and other colors to create a slightly transparent and hazy effect, which was irreplaceable by other pigments in the past. In addition, the durability of this pigment is also very good. It will hardly fade when exposed to the air, and even when exposed to the sun, the color decays slower than other pigments.

Therefore, this "magical oriental pigment" was loaded onto European cargo ships along with jewelry and spices and shipped to Europe, where it became very popular in the European pigment market.

In addition to the aforementioned Van Gogh's "Starry Night", Indian Yellow can also be seen in Rembrandt's "The Parable of the Rich Fool". In Vermeer's "Man Holding a Scale", the color of the window on the left was repaired by later generations, and the pigment used for the repair was also Indian Yellow.

Rembrandt's "Parable of the Rich and Fools", Image source: Wikipedia

Because the raw materials used to make this pigment have a strong ammonia smell, which is a bit like the smell of urine, some people speculated in the 18th century that this pigment might be related to urine. But some people also think that this pigment might be made of turmeric, after all, turmeric also has a special smell (but it is actually different from the smell of urine).

But people didn't think much about it at the time. After all, as long as the paint looked good, it didn't matter what it was made of.

Indian yellow used to make pigment, Image source: Wikipedia

Indian yellow is actually cow urine yellow?

Later in the 19th century, the chemical industry began to rise, and some businessmen began to set their sights on Indian yellow. After all, the cost of importing this pigment from the far east was too high. If it could be synthesized directly using chemical processes, the cost could be greatly reduced and huge profits could be earned.

But if you want to synthesize it artificially, the first step is to figure out what Indian yellow is.

In 1844, chemist and businessman John Stenhouse published an article discussing his thoughts on the origins of Indian yellow.

John Stenhouse, Image source: Wikipedia

The raw materials of Indian yellow are mainly some gray balls. When opened, the inside is yellow. Stenhouse put these yellow things under a microscope and saw very small needle-shaped crystals, which he called "purine acid". In fact, uric acid is also a product of purine metabolism. What Stenhouse saw should be very similar to uric acid crystals, but Stenhouse did not think of urine.

He thought these things smelled a bit like castor oil (maybe different people have different perceptions of smells), so he speculated that this thing should be extracted from plants.

In addition to Stenhouse, many people at the time speculated about the composition of Indian yellow, and some people firmly believed that this substance should be extracted from animal urine.

India was a British colony at the time, and British scientist Joseph Dalton Hooker asked TN Mukharji, director of the Indian Museum, to investigate the origin of Indian yellow.

It turned out that the source of Indian yellow is indeed related to animal urine.

Mukherjee found in the Munger area in northeastern Bihar that some herders would feed their cattle with mango leaves. Because they only ate mango leaves, the health of these cattle was very poor and they were very thin. People would collect the urine of these cows, evaporate it over fire, and then filter and dry it. These processed things were the raw materials for making Indian yellow. After purchasing these raw materials, European merchants would wash and purify them and finally make them into finished pigments.

Mukherjee also found that the raw materials extracted from cow urine by herders were sold for about 1 rupee per pound (about 0.45 kg), but when middlemen resold them to places like Kolkata, the price had soared to 100-200 rupees per pound.

At the same time, Mukherjee also sent Huq a wealth of samples, including raw materials purchased directly from herders, raw materials purchased from the Kolkata market, and even mango leaves and cow urine.

These materials are crucial to determining the origin of Indian yellow's ingredients.

After the 21st century, researchers still analyzed these samples and determined the true source of Indian yellow, which is animal urine. At the same time, they also corrected the spectrum of Indian yellow, because there were many other pigments with the same name as Indian yellow in the past, which had caused some confusion.

Although Indian yellow is a very good pigment, its production process is too cruel. Eating only mango tree leaves will make cows in poor physical condition. Therefore, after the 20th century, there was a movement to boycott Indian yellow. Coupled with the worship of cows by people in many parts of India, traditional Indian yellow has gradually withdrawn from the stage of history.

In this process, artificial yellow dyes also played an important role. After all, they can be synthesized artificially at a low cost, so there is no need to "harm" cattle.

The Age of Innocence, Image source: Wikipedia

The Indian yellow we use now no longer contains cow urine, but these famous paintings have fixed the history of "cow urine yellow".

References:

[1] Stenhouse, John (November 1844). "Examination of a yellow substance from India called Purree, from which the pigment called Indian Yellow is manufactured". London and Edinburgh Philosophical Magazine and Journal of Science. 25: 321–325.

[2] Ploeger R, Shugar A. The story of Indian yellow–excreting a solution[J]. Journal of Cultural Heritage, 2017, 24: 197-205.

[3] https://www.bbc.com/ukchina/simp/vert-cul-45669420

Author: Dai Li Popular Science Author

Reviewer: Gu Miaofei, Ph.D. in Chemical Engineering, Editor and Deputy Editor of Science Pictorial

The article is produced by Science Popularization China-Creation Cultivation Program. Please indicate the source when reprinting.