The common onion does not occur in nature. It has been cultivated for at least 3,000 years, probably developed from the Central Asian onion, Allium oschaninii. The dry outer skin of the onion that protects the bulb is used for dyeing. Even when these skins are red, the colour produced on wool mordanted with alum is always yellow, since the red pigments in the skins, anthocyanins, are not effective dyestuffs.
