Materials for casting a container - WarmGlass.com

Materials for casting a container

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FusedLightStudio
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Joined: Wed Jan 24, 2018 1:33 pm
Location: Georgia
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Materials for casting a container

Postby FusedLightStudio » Sun Dec 15, 2019 10:41 am

I cast some containers (1/2” thick) using vermiculite lined with 1/16” fiber paper. Plaster-silica form in the middle. It worked OK, but the fiber lining was a pain.

I’d like to try:
-Coating the vermiculite with plaster-zircopax mix (40-60). Charlie Holden (whose studio I inherited) had this in his firing notes, but I’ve never tried it and not sure how thick to make it, and whether to coat the board before or after pre-firing the vermiculite

-Any other possibilities for coating vermiculite boxes? Whiting? Super-thick kiln wash?

-Using fiber board - is LD going to hold up as well as the recommended HD? (I don’t know for sure but I think the stock I have is LD)

Would greatly appreciate any notes from experienced casters.
Lisa Schnellinger
Atlanta, GA

Kevin Midgley
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Joined: Mon Mar 10, 2003 11:36 am
Location: Tofino, British Columbia, Canada

Re: Materials for casting a container

Postby Kevin Midgley » Mon Dec 16, 2019 11:46 am

The lower density board will insulate the glass you are heating and make the firing slower and longer. The higher density board would allow more heat transmission through conduction of the kiln heat through the material and into the glass. The lower density board because it is less dense has infinitely more tiny air pockets inside to insulate the glass on the interior of the mold. Think of trying to get heat to penetrate a bunch of glass in a pile on a kiln shelf. You end up with a nicely melted exterior and the powdered glass in the middle of the pile still powder.
You could get rid of the teeny air pockets inside the low density board by filling it, fully saturating it, with a wet mix of whatever you decide to coat the board with. It will have to carry whatever tiny particles it is made up of into those teeny air pockets and replace the air within. No air = heat conduction and your mold will allow the glass inside to melt.
After going to all this trouble, you'd be wise to make the mold last more than one firing with no undercuts etc.
Note I make no recommendations for which material to coat the mold with as each will have their own positive and negative features including particle sizing and how well it will penetrate the low density board. Some wetting agent like Jet Dry might assist in the saturation process but it may also foam and create air bubbles which is exactly what you don't need. You will have to experiment and formulate what works for you. All boards are not created equal either so different brands will have different results.

FusedLightStudio
Posts: 56
Joined: Wed Jan 24, 2018 1:33 pm
Location: Georgia
Contact:

Re: Materials for casting a container

Postby FusedLightStudio » Wed Dec 18, 2019 11:12 pm

Kevin Midgley wrote:The lower density board will insulate the glass you are heating and make the firing slower and longer. The higher density board would allow more heat transmission through conduction of the kiln heat through the material and into the glass. The lower density board because it is less dense has infinitely more tiny air pockets inside to insulate the glass on the interior of the mold. Think of trying to get heat to penetrate a bunch of glass in a pile on a kiln shelf. You end up with a nicely melted exterior and the powdered glass in the middle of the pile still powder.
You could get rid of the teeny air pockets inside the low density board by filling it, fully saturating it, with a wet mix of whatever you decide to coat the board with. It will have to carry whatever tiny particles it is made up of into those teeny air pockets and replace the air within. No air = heat conduction and your mold will allow the glass inside to melt.
After going to all this trouble, you'd be wise to make the mold last more than one firing with no undercuts etc.
Note I make no recommendations for which material to coat the mold with as each will have their own positive and negative features including particle sizing and how well it will penetrate the low density board. Some wetting agent like Jet Dry might assist in the saturation process but it may also foam and create air bubbles which is exactly what you don't need. You will have to experiment and formulate what works for you. All boards are not created equal either so different brands will have different results.



Kevin, thank you so much. Very helpful, and I really appreciate the “why” details.

I did run a test firing. I’m casting this particular project with float glass.

I had given the fiber board several coats of kiln wash. Saturated pretty well, and in the test it performed the same as the vermiculite board that I used in the other three samples (one vermiculite coated with the plaster-zirc, the other two with 1/16” fiber felt).

For anyone who cares, the plaster-zirc worked great. Created lovely texture and left the glass very shiny. Didn’t seem to matter if I applied it before pre-firing or after. Made several batches and the batch that was a ratio of 50ml water to 60g zirc and 40g plaster was the right consistency.

Now onto the full-scale castings!
Lisa Schnellinger
Atlanta, GA


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