Indian yellow, also called euxanthin or euxanthine, is a transparent yellow pigment used in oil painting. Chemically it is a magnesium euxanthate, the magnesium salt of euxanthic acid. It is a clear, deep and luminescent yellow pigment. Its color is deeper than gamboge but less pure than cadmium yellow.
Indian yellow was used by artist painters in both oil paints and watercolors. Due to its fluorescence, it is especially vivid and bright in sunlight. It was likely first used by Dutch artists, and before the end of the 18th century it was commonly used by artists across Europe. Its origin was unknown until an investigation in the year 1883; however, in 2004, Victoria Finlay called this into question.
Indian yellow pigment is claimed to have been originally manufactured in rural India from the urine of cattle fed only on mango leaves and water. The urine was collected and dried, producing foul-smelling hard dirty yellow balls of the raw pigment. The process was allegedly declared inhumane and outlawed in 1908, as the cows were extremely undernourished, partly because the leaves contain the toxin urushiol which is also found in poison ivy.
In her 2004 book Color: A Natural History of the Palette, Victoria Finlay examined whether Indian yellow was really made from cow urine. The only printed source mentioning this practice is a single letter written by a Mr. T.N. Mukharji of Calcutta, who claimed to have seen the color being made. Aside from this letter, there appear to be no written sources from the time period mentioning the production of Indian yellow. Finlay searched for legal records concerning the supposed banning of Indian yellow production in both the India Library in London and the National Library in Calcutta, and found none. She visited the town in India mentioned in Mukharji's letter as the only source of the color, but found no trace of evidence that the color had ever been produced there. None of the locals she spoke with had ever heard of the practice. It is possible that Indian yellow came from another source, and that the cow urine story was fabricated by Mukharji, but came to be accepted by later authors. As such, the viability of producing Indian yellow from the urine of mango-leaf-fed cows is unknown.
The replacement for the original pigment (which was not entirely lightfast), synthetic Indian yellow hue, is a mixture of nickel azo, hansa yellow and quinacridone burnt orange. It is also known as azo yellow light and deep, or nickel azo yellow.