Sometimes known as Genuine Indian Yellow, this extinct yellow pigment is one of those that gets mentioned when lists of outrageous pigments are given. It's helpful to identify it as Euxanthic acid or euxanthin to be sure that it is NY20 which is meant, as today the term Indian Yellow can refer to a large number of other pigments.
This mysterious pigment was allegedly made by feeding cows in India a diet of mango leaves and then processing the urine to create a pigment. It's sometimes debated whether this color actually exists, or at least if it was made in the way that is commonly told and re-told. The color at least does in fact seem to be real--regardless as to whether there was basis in the stories told of how it was manufactured.
The term Indian Yellow or India Yellow has come to connote a warm transparent yellow, though not all paints labeled Indian Yellow match that description.
Golden has pictures of an actual sample of genuine Indian Yellow, or Magnesium salt of euxanthic acid.
Today a wide range of transparent yellows are available to artists, and so the name Indian Yellow applies to a great many paints of other pigments.
In terms of lightfastness, it is helpful to note that the genuine pigment is fugitive.
