beginners questions on molds (if this is the right group)

I'm beginning to try to find a way to make fine-detail reproductions of fossils to have cast into silver jewelry. I have been getting very good, high-detail molds by painting the fossils with latex, but practice plaster-of-paris replicas have been coming out with pits where air-bubbles have been trapped in nooks and crannies of the mold. How do I eliminate those bubbles?

Also, I would, I suppose, have to supply wax casts of the items I need to the jeweler for making molds. What type of wax would I use that would be suitable to use with a latex mold?

And one last question, if I wanted to make sturdy, permanent I'm beginning to try to find a way to make fine-detail reproductions of fossils to have cast into silver jewelry. I have been getting very good, high-detail molds by painting the fossils with latex, but practice plaster-of-paris replicas have been coming out with pits where air-bubbles have been trapped in nooks and crannies of the mold. How do I eliminate those bubbles?

Also, I would, I suppose, have to supply wax casts of the items I need to the jeweler for making molds. What type of wax would I use that would be suitable to use with a latex mold?

And one last question, if I wanted to make sturdy, permanent replicas directly from the mold, what material could I use? Is there a low-melting temp plastic for using with latex molds?

fossils to have cast into painting the fossils with pits where air-bubbles have bubbles?

[I wouldn't worry too much about the plaster positives, since that's not really the material you need to cast in there. You might run into a similar problem with wax, but the solution is different; brushing hot wax into the mold and chasing away the bubbles before they have a chance to chill.] the jeweler for making latex mold?

[Victory Brown, sculptor's mainstay microcrystaline wax, works okay for jewelry. Latex isn't the greatest material for casting wax into, since it erodes, dries out, and tends to stick- but it will work to some extent, especially when fresh. Silicone spray helps to release the wax, but don't use too much since it will soften the wax surface if you do. ] directly from the mold, what latex molds?

[No, but you could use Alumilite or one of the other urethane resin systems. Talcum powder helps to release it, but this is sticky stuff. In general, you'd be better off if you switch from latex to silicone molds. I do a lot of this sort of thing, and I find it far superior. Try it, you'll like it...]

Andrew Werby

add this to Andrew's comment

not only switch to silicone- but to cast wax, pre-heat the mold by filling it with wax and letting it sit till solid ( this will be a 'bad' casting-throw it back in the pot )- the hot mold will prevent the wax from chilling the instant it hits the rubber.

Also- some bubbles may be in the rubber itself- vacuum silicone before pouring R- if you don't have access to a vacuum, then pour the silicone very slow in a pencil lead thin stream- this will eliminate 99% of all air bubble in the mixed rubber.

Also- if you are unfamiliar with wax- realize that it is flammable- to melt it use the kind of deep fryer or stew poit that has a thermostat control on it and set it no higher than 225 degrees F. ( or melt it in a can inside a pot of water- which will limit the temperature to 214 degrees F.)

The resin to cast in depends on the appearance you are after. There are metal filled epoxies and glass filled urethanes and even polyesters, which should also be filled for castings thicker than 2 inches. All these compounds pour at room temperature and work best with silicone molds.

Find a local plastics supplier and go visit- they will have samples of all their materials for your preusal. Christopher