Some time back there was some speculation about using dry plaster inside a mold to keep the sides in place. No real consenseus was reached on whether or not this would work and I was wondering if any of you may have tried it and liked it?
If that isn't clear, consider a bowl shape with glass up the sides. Now, pack dry plaster into the inside to keep the sides where they belong, or that's the idea. Some of the old masters used asbestos pretty well, but I think I'll stay away from that one.
Thanks,
Jerry
Dry plaster plugs
Moderator: Brad Walker
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Lauri Levanto
- Posts: 270
- Joined: Tue Mar 11, 2003 7:33 am
- Location: Halikko, Finland
Jerry,
as you have realized, you can use a nonsolid plug only if the glass is kept in place otherwise, that is pate de verre.
Then two questions are left:
Does the glue have enough time and room to vaporise away?
When the glass is fused, it is packed more closely. Is there a risk of plaster particle inclusions. Plaster appears to shrink
in higher temperatures. Does the powder plug then sag too much?
Instead of dry plaster, I'll test with luto, that is used mold material. It should be more inert, as all materials are
calcinated, no longer releasing chemically bonded water.
-lauri
as you have realized, you can use a nonsolid plug only if the glass is kept in place otherwise, that is pate de verre.
Then two questions are left:
Does the glue have enough time and room to vaporise away?
When the glass is fused, it is packed more closely. Is there a risk of plaster particle inclusions. Plaster appears to shrink
in higher temperatures. Does the powder plug then sag too much?
Instead of dry plaster, I'll test with luto, that is used mold material. It should be more inert, as all materials are
calcinated, no longer releasing chemically bonded water.
-lauri
ON THIS SITUATION OF CALCINATED, NO LONGER RELEASING CHEMICALLY BONDED WATER,,,,lauri wrote:Jerry,
as you have realized, you can use a nonsolid plug only if the glass is kept in place otherwise, that is pate de verre.
Then two questions are left:
Does the glue have enough time and room to vaporise away?
When the glass is fused, it is packed more closely. Is there a risk of plaster particle inclusions. Plaster appears to shrink
in higher temperatures. Does the powder plug then sag too much?
Instead of dry plaster, I'll test with luto, that is used mold material. It should be more inert, as all materials are
calcinated, no longer releasing chemically bonded water.
-lauri
is the release of this water, what makes the mold stick to the glass
is this calcinate mold material what is call GROG
it seems that if the pate de verre is place along the wall of the mold and the powdered material is pour and tamped down, that once the glass begins to sag and flow, the powder would get mixed into the surface, why is this not happening
as always, thanks for the info
rodney
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Colin & Helen
- Posts: 44
- Joined: Fri May 16, 2003 7:21 pm
- Location: Albany Western Australia
is this calcinate mold material what is call GROG
rodney[/quote]
Rodney .. Calcine is to purify by the action of heat..grog is ground fired clay body..Colin
rodney[/quote]
Rodney .. Calcine is to purify by the action of heat..grog is ground fired clay body..Colin
Colin & Helen from the other albany<img src="http://members.westnet.com.au/sheltie/i ... b-logo.jpg">
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Lauri Levanto
- Posts: 270
- Joined: Tue Mar 11, 2003 7:33 am
- Location: Halikko, Finland
> ON THIS SITUATION OF CALCINATED, NO >LONGER RELEASING CHEMICALLY BONDED WATER,,,,
> is the release of this water, what makes the >mold stick to the glass
I do not think so. My suspect is the ceramic compounds
in the mold mixture. They start to sinter or fuse
at the higher temperatures. Was it Hugo's recipe for kiln was that used less reactive kaolin just to prevent it hardening.
My kiln wash is 1/3 plaster 2/3 aluminium oxide.
> is this calcinate mold material what is call GROG
Grog is whatwe in old Europe call Chamotte, fired clay that
is ground.
My molds material consist of plaster, grogg and kaolin.
When it is used, the kaolin turns to grogg that is less reactive, plaster is calcinated, reacting no longer with water.
> it seems that if the pate de verre is place along >the wall of the mold and the powdered material is pour and >tamped down, that once the glass begins to sag and flow, >the powder
> would get mixed into the surface, why is this not happening
I have not much experience with pate de verre, only a couple of experiments. *This is just a guess*:
When the frit starts to melt, it first beads up to spheres due to surface tension. Then the beads fuse to a continuous layer.
The surface tension of the glass tends to hold the solid
material outside.
If f.ex dry plaster is used as a plug when the pate de verre layer is still wet, it will absorb some water from the pate and
form a solidified skin round the remaining plaster powder. This skin will form numerous hairline cracks of course.
> as always, thanks for the info
That's the why we all are here.
- lauri
p.s. Next month I take a course of pate de verre,
then I'll even KNOW something, not only think about.
> is the release of this water, what makes the >mold stick to the glass
I do not think so. My suspect is the ceramic compounds
in the mold mixture. They start to sinter or fuse
at the higher temperatures. Was it Hugo's recipe for kiln was that used less reactive kaolin just to prevent it hardening.
My kiln wash is 1/3 plaster 2/3 aluminium oxide.
> is this calcinate mold material what is call GROG
Grog is whatwe in old Europe call Chamotte, fired clay that
is ground.
My molds material consist of plaster, grogg and kaolin.
When it is used, the kaolin turns to grogg that is less reactive, plaster is calcinated, reacting no longer with water.
> it seems that if the pate de verre is place along >the wall of the mold and the powdered material is pour and >tamped down, that once the glass begins to sag and flow, >the powder
> would get mixed into the surface, why is this not happening
I have not much experience with pate de verre, only a couple of experiments. *This is just a guess*:
When the frit starts to melt, it first beads up to spheres due to surface tension. Then the beads fuse to a continuous layer.
The surface tension of the glass tends to hold the solid
material outside.
If f.ex dry plaster is used as a plug when the pate de verre layer is still wet, it will absorb some water from the pate and
form a solidified skin round the remaining plaster powder. This skin will form numerous hairline cracks of course.
> as always, thanks for the info
That's the why we all are here.
- lauri
p.s. Next month I take a course of pate de verre,
then I'll even KNOW something, not only think about.
-
Jerry
dry plaster plug
Okay folks, it's all done and I have results to share.
The idea of using talc was a good one. After I had the glass in place up the sides with CMC as a binder I packed talc into the void area. The glass consolidated, of course, but the talc held it in place pretty well; I'm pleased.
I think there may be something to be said for doing a tack firing after the glass is in place, then adding the talc and going to process temps. That way I can see if there is any additional glass needed.
Anyway, for all the help, thanks.
And, just for the record, "Grog" is a drink, as any sailor can tell you, especially after having a few of them.
Jerry
The idea of using talc was a good one. After I had the glass in place up the sides with CMC as a binder I packed talc into the void area. The glass consolidated, of course, but the talc held it in place pretty well; I'm pleased.
I think there may be something to be said for doing a tack firing after the glass is in place, then adding the talc and going to process temps. That way I can see if there is any additional glass needed.
Anyway, for all the help, thanks.
And, just for the record, "Grog" is a drink, as any sailor can tell you, especially after having a few of them.
Jerry