Best to do more than warm it. Any residual moisture can cause a
steam bubble that will throw molten pewter around, not a good
scenario. For jewelry scale molds heat the plaster to at least 300
degrees F for an hour to make sure the water has been driven from
Depends how much you use, the size of the plaster mould, and how dry
the plaster is. Pewter is pretty much a doddle, of course you are
correct it’s better to have a warm mould, although I have moulded
pewter in a cold mould with success. I used to make a lot of model
soldiers out of pewter when I was eight.
I did make a model of a demon head I saw in a movie, around about
the same time, and instead of using pewter I used lead, and the
plaster mould was quite large, about the size of an eight year old’s
fist. I didn’t let the plaster dry long enough, and poured the molten
lead into the mould. Result lead volcano. I didn’t make that mistake
again. I used to cook the plaster a little after that.
Plaster is something you can use for pewter, and can be quite safe
if you take care. However Dowe Corning has some very nice RTV that is
flexible, which is a big plus over plaster.
Regards Charles A.
P.S. I consider a kitchen oven “warm”