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I'm getting trapped air bubbles using hydroperm as a mold for slumping panels for a bent panel lamp. The panels are odd shaped with lots of dents. I'm thinking that there might be 2 causes.

#1. I am ramping up extremely fast to 1400 after the initial slow heat up to 1000. This is to try and avoid devit. My denver can do it in about 10 miniuts which I'm thinking is maybe to fast and is not long enough for the air to escape through the plaster.

#2, I mixed a batch 1.5 part plaster to 1 part water, whipped it up and got a pretty frothy and what I thought was thin mix. So I added more plaster next time, 2 part plaster to 1 part water. got something more like a batter but not frothy and no visible bubbles after the whipping. So maybe if its to thick it wont have the bubbles necessary to make air escape holes?

What do y'all think
Liam
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I don't think many people here use hydroperm. The best thing I can say is you should look at Kervin and Fenton's book on casting to get their recommendations on mixing. They write a bit about hydroperm.

I don't think you should need to go to 1400 though. I would go very slowly from 1000 to about 1250 tops. This should give the air time to work its way out while the glass slowly slumps.

Hydraperm has very specific quantities of plaster and water in it's mix, and even the size of impeller that you beat it with is specified. I haven't used it in years, but when I did we took great care to mix the quantities exactly, and to use the right impeller. This is important because Hydraperm is a permeable mold material. The trapped air and moisture in the mold is driven out, by heat, through an interlocking network of tiny bubbles, .005" if I remember. That is the reason that you can cast a Hydraperm mold and use it immediately. No 3 day air drying, no pre-firing, cast and go. If you aren't using it for that purpose, then why not just go to a less expensive casting plaster? Brock

the drying time is one reason that I'm using it. But the biggest is that I'm trying to duplicate a heavy texture on stained glass. Trying to get as much glass into crevices without 1000 drill holes isn't easy. So this is what I'm trying. going to go way slow to see if it works.
Still needed to drill holes to get full contact in concave bent panel mold, so I'm not really optamistic.
Got a cool tip from Javahut on newsgroups. Add some 1/32 milled fiberglass to strengthen the mold. Fired 5 times > 1300 before any degradation

Liam

Liam wrote:the drying time is one reason that I'm using it. But the biggest is that I'm trying to duplicate a heavy texture on stained glass. Trying to get as much glass into crevices without 1000 drill holes isn't easy. So this is what I'm trying. going to go way slow to see if it works.
Still needed to drill holes to get full contact in concave bent panel mold, so I'm not really optamistic.
Got a cool tip from Javahut on newsgroups. Add some 1/32 milled fiberglass to strengthen the mold. Fired 5 times > 1300 before any degradation

Liam

Hmmm . . . I'll have to watch it again, but I'm pretty sure that in the "Mixing With the Best" CD, they have discounted that fibreglass thread inclusion. I've used them too, but I think it may be of no real use. Brock

Brock wrote:

Liam wrote:the drying time is one reason that I'm using it. But the biggest is that I'm trying to duplicate a heavy texture on stained glass. Trying to get as much glass into crevices without 1000 drill holes isn't easy. So this is what I'm trying. going to go way slow to see if it works.
Still needed to drill holes to get full contact in concave bent panel mold, so I'm not really optamistic.
Got a cool tip from Javahut on newsgroups. Add some 1/32 milled fiberglass to strengthen the mold. Fired 5 times > 1300 before any degradation

Liam

Hmmm . . . I'll have to watch it again, but I'm pretty sure that in the "Mixing With the Best" CD, they have discounted that fibreglass thread inclusion. I've used them too, but I think it may be of no real use. Brock

Yup!

I looked it up. To paraphrase briefly, (cause the CD won't let me cut and paste) . . . "fibreglass increases the strength of the mold in the drying and curing temperatures, (much like straw mixed with adobe brick) . . .

However . . . when melted between 850 - 950C (1562 - 1742F) it melts and surives in the mold as a network of glassy threads. These glassy threads, instead of detracting from he strength of the clay . . . may actually increase the modulus of rupture of the fired body. Brock

A relative of mine works at a cement manufacturer.
I asked him what happens to plaster at 700-740 C
when it develops cracks. His lab colleagues told that:

"(the calcuim sulfate turns to calcium oxide and sulphuric
vapors)

The cracks usually form at calcination stage 42-240C but come visible at the higher temps."

My comments:If so then the fiberglass may have a positive effect. The same effect one can achieve by adding
cellulose (paper) fiber. This is mentioned by Lundstrom, who
warns that water absorbing fibers make the correct
mixing difficult.

-lauri

Liam

The answer is simple. Don't go so hot. Pick a much lower temp and soak there. You can try and carve some texture as well.

As to the fiberglass melting at higher temperatures, that's because they used soda-lime fiberglass. If they had used borosilicate fiberglass it wouldn't have melted.

charlie holden wrote:As to the fiberglass melting at higher temperatures, that's because they used soda-lime fiberglass. If they had used borosilicate fiberglass it wouldn't have melted.

True. I just re-checked, and evidently they didn't test borosilicate fiberglass. BTW Charlie, I missed you at Pilchuck twice this year.
Another time. Brock

Brock wrote:

Brock wrote:

Liam wrote:the drying time is one reason that I'm using it. But the biggest is that I'm trying to duplicate a heavy texture on stained glass. Trying to get as much glass into crevices without 1000 drill holes isn't easy. So this is what I'm trying. going to go way slow to see if it works.
Still needed to drill holes to get full contact in concave bent panel mold, so I'm not really optamistic.
Got a cool tip from Javahut on newsgroups. Add some 1/32 milled fiberglass to strengthen the mold. Fired 5 times > 1300 before any degradation

Liam

Hmmm . . . I'll have to watch it again, but I'm pretty sure that in the "Mixing With the Best" CD, they have discounted that fibreglass thread inclusion. I've used them too, but I think it may be of no real use. Brock

Yup!

I looked it up. To paraphrase briefly, (cause the CD won't let me cut and paste) . . . "fibreglass increases the strength of the mold in the drying and curing temperatures, (much like straw mixed with adobe brick) . . .

However . . . when melted between 850 - 950C (1562 - 1742F) it melts and surives in the mold as a network of glassy threads. These glassy threads, instead of detracting from he strength of the clay . . . may actually increase the modulus of rupture of the fired body. Brock

I wonder though if you dont exceed 850, do the strands remain unmelted, and add to the strength? Does anyone know a resource for the melting/softenting temperature of fiberglass thread? If it is 850, then there should still have some merit for slumping.


Liam

Brock wrote:

charlie holden wrote:As to the fiberglass melting at higher temperatures, that's because they used soda-lime fiberglass. If they had used borosilicate fiberglass it wouldn't have melted.

True. I just re-checked, and evidently they didn't test borosilicate fiberglass. BTW Charlie, I missed you at Pilchuck twice this year.
Another time. Brock

I think it was more than that. Doug said you were by twice first session. I was there first and fourth sessions as a student, then fifth session as emergency TA for Mitchel Gaudet. Somebody mentioned you had dropped by fifth session. Hope to TA again next summer, if GAS doesn't get in the way. Maybe then.

ch

I think it was more than that. Doug said you were by twice first session. I was there first and fourth sessions as a student, then fifth session as emergency TA for Mitchel Gaudet. Somebody mentioned you had dropped by fifth session. Hope to TA again next summer, if GAS doesn't get in the way. Maybe then.

ch

TA is a tough job. Mitchell didn't wear you out? Brock