[msds]

Wax is a very good material for modifying/smoothing prints pre-casting, and doesn't mess with the casting process. UV-cure resin is also a good choice, as you can set it fully, sand it down, and apply a gel-coat for a shiny finish.

ABS is a very bad material for casting if you're planning on burning it out, but vapor smoothed parts do make very nice plaster molds if you can remove them. Chloroform works very well for PLA, but it is much much nastier.