Re: RP and Jewelry Question

From: Bathsheba Grossman (
Date: Mon Oct 27 2003 - 20:56:31 EET

On Mon, 27 Oct 2003, Scott Tilton wrote:
> My question is, are they using the Perfactory parts as the investment
> (making a ceramic mold around it and then burning off the RP part?)
> Or are they making wax copies of the Perfactory parts to burn off? (using
> some sort of soft -- rubberish tooling)

They could be doing either. There exists a burnout protocol for
Perfactory parts, and although it is long and uses high temperatures,
I'm told it works.

> I had an older person from the jewelry industry tell me about when they made
> molds around patterns for creating wax duplicates.
> He said that the pattern would be fixtued in a holder, and then rubber
> pellets were packed in all around it.
> They they'd put it in the oven at 250F or so and let the rubber melt around
> the pattern.

This is the process for making a vulcanized mold. It is used for
making a mold off a metal master, or anything else that can stand the
temperature and pressure -- the heating is done in a press that
squeezes the rubber around the part.

For molding a weak part, like most RP parts, RTV rubber would be used.
Most moldmaking jewelers are able to use both types of mold. RTV is
useful where absolutely 0% shrinkage is required.

If you're wondering why anyone ever uses the more cumbersome process,
it's because vulcanized rubber is much tougher and stronger than RTV.
It can stand thousands of shots, it's got a great shelf life, it has
terrific memory so molds can be stored's just better stuff.

Hope this helps,


Bathsheba Grossman                 phone (831)429-8224, fax (831)460-1242
Sculpting geometry                                
Solidscape prototyping                           
Protein crystals                             

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