Moldmaking plaster molds..is this a no no.

The main problem with plaster molds (though there could be the reaction factor- I really have no idea about that...) is undercuts. Those are places that can get caught in your mold- you might not even be able to get your original out of a mold if there are too many undercuts. Silicone give you the flexibility to make that not matter as much. Also you would most likely have to use more than two pieces for a head and such, depending on the complexity of your piece, which means more seamlines. With a rubber mold you can have two seams or one seam and sometimes (with more stretch) no seams at all, even.

It can be done plaster, however:
Here is the diary of a doll artist who uses plaster molds to cast his dolls in clay slip, I think...

http://doll.mda.or.jp/~naruto/

If you look through the Diary section you'll see a lot of helpful pictures. Most of the mold-making pictures are fairly far back. It's worth a look for all the prettiness, too

 

What we learned in sculpture is if you're casting something soft, your mold needs to be hard. Casting something hard, and your mold needs to be soft and flexible. You CAN cast plaster from plaster molds... but you usually destroy your mold in the process. The same would be true I'd assume with resin... But, you could do it if you just want one cast from it. :3 Destroying the mold gets you around the undercut problem. I'd assume you could make at least two casts with latex... the problem is that it doesn't stand up to a lot of casting. Even silicone won't stand up to hundreds and hundreds of castings, but apparently it lasts a lot longer than the latex.

For Bastian's head it takes about an inch of resin in a plastic cup. So I'd guess you'd need about four pints of resin for a full doll? The resin you get standard in Smooth-on's super sampler sets up in 15 minutes, faster if it has color to it. By the time I pour both head and head cap, the head is almost to the gel state, where you can't stamp any airbubbles out(you shake the mold and hit it against the table firmly to make the air bubbles rise). I just bought 30 minute set up time resin for when I start casting whole dolls from the same color... hopefully that'll give me a long enough work time to get them all poured. I still might have to have someone going along after me, shaking the molds. X3

 

uhhgg totally wrong post sorry ignore this

 

I would say a no-no. I tried once and I had to redo everything. The plaster tried to "drink" the plastic, so it was not a good idea.