Plaster Molds

[sw282]

Anybody here cast using a plaster mold? A local stain glass maker wants me to cast some finials for them. He said they had tried but could not get the mold to fill out. The finial molds are made of plaster

[DukeInFlorida]

Plaster is tough to remove all moisture from. Bake the mold in an oven after allowing it to dry for a week.

Like any casting mold (boolits, for example), it needs to be up to temperature otherwise the mold surfaces will start to chill off the metal, and will block the pouring metal.

Plaster is porous enough that venting shouldn't be an issue.

Are we presuming lead is the metal for the finials?

If it's higher temp metal, other issues come into play.

[2wheelDuke]

How big are the finials, and how big are the molds?

[docone31]

You have to heat in a kiln. I would use RTV Rubber for the molds. I use that for doing things like fruit for casting.
Pour into a mold, at an angle, then spin it around at the end of a chain to remove bubbles. Let sit, cut out the item to be molded, and cut a sprue.
Works real well.

[reg293]

Look up " lost wax casting", it my be of some help to you.

[dnepr]

Did it once , got a visit from the tinsel fairy while playing with molten aluminum , MAKE SURE the moisture is out of the mold

[runfiverun]

docone31 could tell you more than you wanted to know about lost wax casting.
i would get more of his imput.