Re: steam defects-drying out plaster mold

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Posted by bruce paul fink on December 10, 1999 at 08:29:50:

In Reply to: Re: steam defects-drying out plaster mold posted by John Odom on December 10, 1999 at 07:52:53:

Thanks again John.

I DIDN'T know that.

My first burnout temperature college advice in 1960 said

IT HAD to be 1500F.

It also said you needed to use asbestos as an ingredient to help the investment not crack in the shrinkage and shock. (Back then you bought it at the local hardware store in 50 lb. bags, was real cheap and nearly every home had it on it's heat pipes for insulation... ah ignorance.)

We tried alternatives from exploded mica to fine saw dust (it burned out but left a micro space in the process) to detergents that were whipped in to make mini air cavities. They helped but still got the flashing.

Then I wondered why the 1500F was needed and started to cut down on the heat and use a nose test for the gauge to see if they were still holding any wax residue and if the chemical water was hopefully gone or left locked in (hey what did I know, I was an Industrial Designer and sculptor, not a chemist. It is a small nose but a good nose).

Next step was 1200 F... it still worked, still some flashing

then 1000F... less flashing and still working

then 900F... nearly no flashing now and working fine.

I pushed lower till only 700F and it still worked but started to need a longer burnout time and (In my case an extra day and a half because the molds were in the 700 to 2000 lb range) I was not seeing any more or less flashing.

I have now settled on 900F and keep to that on a regular basis.

And I am happy :-)

Thanks John for the further input and I will be waiting for the next revelation to figure out what's up and why.

bpfink


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