Answer: It all depends on what gemstone you’re cutting and also personal preference.
Black, Red/Brown, or Green Faceting Wax?
I have used all three types. Each has a different melting point, so consult the instructions carefully for whatever type you pick.
Like most faceters I know, I use the black wax for almost everything. I’ve tried the red/brown wax and liked it well enough. This variety is also called “diamond setters cement” and has a high melting point. However, I found the black wax easier to work with than red/brown and less noxious smelling when heated. Nevertheless, you can certainly find faceters that swear by the red/brown wax.
Green is the best wax for very heat sensitive stones, such as opal. For opal, I only only use the green wax. It melts at a lower temperature but also has a greater chance of allowing the stone to shift on the dop. I have two very bright, hence warm, incandescent lights that I use while faceting.
J. Sean Keane