How can I make a plastic mold?

[Mimi Melophile]

Here's the scoop - I'm trying to make a chocolate skeleton for a cake decoration. I've made a skeleton out of plaster of paris, and I need to figure out how to make a plastic mold of the plaster so I can have a mold for the chocolate. I thought about fusing plastic bags to the plaster, but I don't know how to do it, or if that even works. What can I do?

((Hoping I'm in the right topic - I figured ceramics, clay, whatever. I used plaster, I figure people in this forum use molds... Never ventured over here before, so I hope this is the right place! ))

[CatCrafter]

Are you familiar with a "vacuuform" ? It was a Mattel toy made in the late 60's. With it kids could make toys out of plastic. One half of the machine would heat the plastic sheet, then when flipped over the sheet would be pressed down onto the chosen form and a pump would vacuum seal the plastic tight over the form.

There are people who do just this on a larger scale in their own homes. They buy the sheets of plastic and heat them in a low oven. Then they use a home made vacuum table to mold the plastic around what they want to copy.

You could do this using things you have right at home. Many things come in plastic blister packs. Save some of this plastic, the flatter the better. These plastic sheets can be heated in your oven or with a heat gun. Then, when hot and pliable the plastic sheet can be formed over the plaster skeleton by pressing down and pushing the plastic by hand around all the curves and crevices. The plastic can be reheated by using a heat gun on whatever area needs to be redone.

This will only make a copy of one half of the skeleton. It will come out kinda like a jelly or candy mold. You would have to make another mold of the 'back' of the skeleton for a 3D copy. The two molds would be filled separately then the two chocolate halves fitted together using melted chocolate to 'glue' them together.

I hope this helps you. let us know how it comes out!       

[littlewrenpottery]

I was about to say sounds like you need a injection mould, the process that cat has described is pretty similar.

The usual way of making molds in pottery is carving something out of clay then encasing it in plaster but this wouldnt have worked in this instance. Tricky question!