Pigments

http://webexhibits.org/pigments/intro/

The above website gives a basic history of pigments, as well as numerous detailed articles about specific pigments.

While they do have a great deal of information, what I found the most interesting was the bit about how oil paints do not dry due to evaporation, but instead oxidize when they come in contact with the air. Clearly this does not change much in practice, but I never would have guessed. I also found it intriguing that the type of pigment suspended in the oil can significantly increase or reduce the speed at which the paint dries.

I thought this site was a well put together introduction to pigments and the like for somebody like me who has never had the pleasure of making their own paint before.

http://essentialvermeer.20m.com/palette/palette_anatomy_of%20_paint.htm

This site used to provide a nice guide to creating egg tempera paint, but for whatever reason was removed just recently (thus this edit.) I'll have to locate another. Oh, woe.