Thanks Matt, great to hear about your sculpture casting experience in France. That must have been really interesting to be a part of.
And Tom thanks for the references that adds even more "takes" on investment casting. Obviously there is a huge range of opinion and procedure.
Now let me clarify my question, because I haven't seen in any of the above information the actual answer to it. Yes there is lots of information about investment casting practice, but that isn't what I want to know.
I want to know at what specific temperature CaSO4·2H2O calcines, that is, loses its bound water. Not recipes for heating molds with plaster(s).
And 140C to 180C mentioned above (if correct) is kind of a big range for a straightforward chemical reaction process, I think it's probably more specific.
Once I understand what the calcining temperature of plaster actually is, then I can move on to understanding other parts of the molding process, and truly WHY differing heat schedules are used by different people. But first things first. Lets get the basics down.
I do truly appreciate the responses, btw!
ps. I gotta say though -- the guy who did his master's degree thesis on investment casting -- that is one of the most complex, cost ineffective means of producing a rough aluminum casting with scabby finish I have ever seen! I can straight sand cast a better looking part in a half hour with a simple charcoal furnace. Not trying to brag, here, just, that kind of complexity is absolutely unnecessary -- a 3D printer, 49% fused alumina content, 24 hours of fuel for kilning, ten risers and a tooled flask, sheesh!