Gamboge is a gum resin that is collected much like rubber. Unlike rubber though, the resin is collected almost an entire year after the slashes are made in the trunk. It is extremely expensive and as far as I know, comes from both Cambodia and Vietnam, though it is named for the former. I remember reading a post sometime back in which you mentioned Mangosteen, Mr.B. The Gamboge tree is related to the Mangosteen. The dried resin is dirty brown in colour but when mixed in water, it turns into a brilliant, almost fluourescent, yellow. Gamboge is a natural purgative and diuretic too

There is another form of yellow, Orpiment. This is a mineral; I cannot remember the chemical compound but it has arsenic and is therefore rarely used. There is a rare, exotic and ceremonial fabric (or is it a costume) in Indonesia, that is dyed almost exclusively with Orpiment. Do you know more about this?