Xanthoproteic acid

If proteins are present that contains amino acids with aromatic rings, the mixture turns yellow[citation needed].

Upon adding a strong base, such as ammonia solution (NH4OH), the color turns orange[citation needed].

These color changes are caused by nitrated aromatic rings in the protein[citation needed].

The xanthoproteic test is specific for aromatic compounds such as tyrosine, tryptophan and phenylalanine[citation needed].

Minor stains are harmless and resolve in a few days[citation needed].