making negative plaster mold from a positive plaster mold

[zombyfellow]

I have a positive plaster mold/copy of a body part which I created using alginate and plaster bandages. Now I would like to create a negative plaster mold by pouring plaster over the positive mold. My question is, what do i cover or spray (if anything) on the plaster positive so it wont stick to the negative that i will pour on top of it? I heard of synlube 531 mold release spray but I believe that is used on top of clay so it wont stick to polyurethane or rubber. The positive (and the negative I want to make ) is made from hydrocal (a hard plaster with a quick set time)
thanks

[Pzak]

I have always had good success with Vasoline.

[zombyfellow]

thanks

[Merlion]

I am not familiar with alginate. The separator I use for plaster cast in plaster molds, I just brush wet clay on the plaster molds. This works very well.

[Alfred]

I've made alot of waste molds in my day and I always use Murphy's Oil Soap. Very thin layers allowed to soak in and then it works just fine. If there's any deep areas, pay special attention to those. Also, because the oil soap soaks into the plaster, you don't loose the details.

Don't forget... very thin coats (2-3) and don't let it pool.

Good Luck,

Alfred

[CroftonGraphics]

I have some air cried clay models I want to make a plaster negative out of them, any advice? Can I do it without destroying the original?

Thanks.

[rhendriks]

I think Latex or silicone is better to make a mold from your airdry
clay model,if you don't want to damage it.It depends also on the form.

Rob
See My Foam Reliefs

[CroftonGraphics]

Ok, thanks I am going to buy some in soon.
Should I coat the air dry surface in something to prevent absorbtion or something?

[GlennT]

To add another method to the original question:

I have taught a number of bas-relief classes to both children and adults. After making a plaster mold, we pour plaster casts. I have had 100% success in about 40 casts by first using liquid dishwashing soap ( for hand washing dishes, not machine ) to cover the entire surface until it is all absorbed, and excess wiped awy. Then we coat the entire surface with a THIN layer of vaseline, removing excess. Too thick will add vaseline texture to the cast.

Exercise due care in seperating the two, by patiently working around the form rather than trying to pry it apart all at once from one point. Also, be prepared to sacrifice the mold. Sometimes they emerge intact, sometimes a piece or two will sheer apart. But the casts have always come out fine.

[rhendriks]

Crofton,I don't know if you need a coat.
I applied the latex without coat ,but my airdry claymodel was varnished.Test it first.

Rob
See My Foam Reliefs