Gamboge? It is a resin tapped from the Garcinia evergreen tree found in South East Asia, which when processed produces the mustardy orange/yellow pigment seen in the monks robes of South East Asia.
It is also a strong laxative and diuretic so excellent studio practice is advised, seriously though it is toxic and should be handled with care.
It has been found in Rembrandt and Turner's work and like so many of these older pigments has been replaced by chemical alternatives.
It is quite thin in body and paints 'long', it's masstone hue is like a rusty water colour, as soon as you spread it out with a palette knife luminous yellow hues appear like magic. It is a gentle tinter, the tints are almost a yellow ochre hue but more vibrant.
It has a reputation for not being entirely lightfast which you should be aware of, however it is a very rare paint now with a wonderfully organic hue and has a depth which naturally sourced pigments often have, so maybe your work won't last for hundreds of years but as all painters know it is the process that matters not the result.
Quite frankly it is fascinating, the range of qualities from masstone, to glaze to tint are very wide. Having used quite a few of these older pigments now I realise just how much more character paints used to have and although I appreciate the improved lightfastness and lessened toxicity with modern paints, it is quite sad how little they vary and truly surprise you.
Pigment - Genuine Gamboge
Binder - Linseed Oil
Opacity - Transparent
Very interesting and unique paint! Looking at a portion of it you see (what looks like) these nifty vibrating particles popping in and out of solution. Everything James said above is accurate.
A modern use I found for it is outdoor oil sketching. Indicate sunlight, without a lot of mixing or thinners? You can do that with this paint straight out of the tube. Color varies depending on pressure applied - just fascinating! I also found this paint is great for harmonizing the cadmium colors with nature. I wouldn't use it on a work for sale due to fading concerns, however Gamboge certainly has a place in my studies, sketches, and mastercopies!