Pate de verre cracking - WarmGlass.com

Pate de verre cracking

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Barb R
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Pate de verre cracking

Postby Barb R » Sat Nov 30, 2013 8:00 pm

DSCN0229-web.jpg
I am playing around with Pate de Verre trying to learn something new. Our local art museum has a fundraiser every year where they hand out ceramic masks to artists to decorate/create and then turn back in for a silent auction. I took my mask (she's not very pretty, but that's okay), and added hair and created rubber silicone mold and then poured a wax. I poured R&R910 over this and steamed out the wax. I packed in fine frit and attempted a fire. The first time I didn't get enough glass in her, and there were holes around the hair line. I poured a new mold over her (R&R 910), added more glass and attempted firing again. Where her long hair meets her face, it's cracked. I'm pretty sure it's an annealing issue - the mold is rather thick there because the hair isn't as deep as her big nose. With this poured mold, if my glass is about 1/4" thick after casting, but the mold is 3 1/2" deep (it's open face), about 1" thick around her face, but abut 2 1/2" thick by this hair extension. How thick should I anneal for? This firing was based on 1 1/2 inches thick (bullseye's recommended annealing schedule). I want to try to fire her again - the mold seems to be in good shape. Should I give up and paint a mold over her to get a more even coverage?

Barb

Kevin Midgley
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Re: Pate de verre cracking

Postby Kevin Midgley » Sun Dec 01, 2013 1:59 am

Maybe you should trying reading Stone's firing schedules for glass a few times cover to cover?
Given the description, your schedule is woefully inadequate. :oops:

Morganica
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Re: Pate de verre cracking

Postby Morganica » Sun Dec 01, 2013 3:32 am

It might not actually be the schedule.

Is the piece intended to be hollow? I do hollow pate de verre portraits that are packed to about 7/8 inch, on average, and they'll wind up a little less than 3/8 in most places--you anneal for the smallest thickness in the shortest dimension. Typically, my noses are thickest, to about a half inch when fired. So I start with an anneal for a half-inch, then double it because of all the variance in thickness. Then I add the thickness of the refractory (one good reason to hand-build on the thin side). All told, I would anneal for about 1.5 inches in a piece like this:
Image
I think, though, that you've got another issue to contend with, whether there's an annealing problem or not. Your piece is relatively symmetrical...except for that curl of hair. I think what's happening is that the glass is contracting and pulling against the mold at what's probably the thinnest and most extreme angle of the whole piece, and the R&R910 is too strong for it. If that's the problem, no amount of annealing will resolve it.

If it's a mold problem, couple ways to fix it. You can weaken the refractory at that point, so that it will crumble instead of fighting the glass. I usually do that by building a very thin facecoat over the area first. Then I mix some organic material into a small amount of refractory--shredded paper, crumbled dry leaves, finely chopped veggie peelings from the kitchen, whatever--and plaster at least a half inch all around the vulnerable area. Then I build the mold as normal around the rest of the piece. (Just don't mix in any material that expands with moist heat, such as rice, oatmeal, etc.--it can cause the mold to crack during the drying process)

The organic material will burn out around 700F, leaving lots of small holes, so that the mold around the vulnerable area resembles swiss cheese. When the glass starts to contract, the holes act as little shock absorbers, letting the mold material compact with the glass.

The other thing you could do is remove the curl or change its direction, so that it's curling into/onto/alongside the face and can contract with the rest of the piece.
Cynthia Morgan
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Kevin Midgley
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Re: Pate de verre cracking

Postby Kevin Midgley » Sun Dec 01, 2013 12:06 pm

but abut 2 1/2" thick by this hair
Yikes!!!!
Making the mold more flexible/forgiving will not compensate.
There's classic heat differential in there.
Understanding Stones book will explain.
Brian Blanthorn's term he used in these situations, evenivity says it all.

Tom Fuhrman
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Re: Pate de verre cracking

Postby Tom Fuhrman » Sun Dec 01, 2013 12:10 pm

Is that photo of one of your pate de verre pieces, if so,
It is tremendous, both technically and as artistic expression. Love it.
What's the size of it?

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Re: Pate de verre cracking

Postby Brad Walker » Sun Dec 01, 2013 12:44 pm

Kevin Midgley wrote:
but abut 2 1/2" thick by this hair
Yikes!!!!
Making the mold more flexible/forgiving will not compensate.
There's classic heat differential in there.
Understanding Stones book will explain.
Brian Blanthorn's term he used in these situations, evenivity says it all.


Don't understand your comment, Kevin. If the mold -- not the glass, which Barb says is only 1/4" thick after firing -- is 2 1/2" thick by the hair, then making the mold narrower and more flexible/forgiving will help. Stone's book recommends keeping the mold to around 1 1/4" thick and as even as possible (pg 34). Changing the mold thickness will greatly simplify the annealing task.

I agree with Cynthia. Most likely, this isn't primarily an annealing issue. It's an issue of a mold that's too dense and glass that is contracting around the mold.

Morganica
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Re: Pate de verre cracking

Postby Morganica » Sun Dec 01, 2013 12:59 pm

Kevin Midgley wrote:
but abut 2 1/2" thick by this hair
Yikes!!!!l
Making the mold more flexible/forgiving will not compensate.
There's classic heat differential in there.
Understanding Stones book will explain.
Brian Blanthorn's term he used in these situations, evenivity says it all.

Not quite. Look at the picture, Kevin. If that glass curl is 2.5 inches thick, then how much thicker is that piece at the nose? She's talking about the thickness of the mold at that point, not the thickness of the glass. 2.5 inches of R&R910 is like reinforced concrete, and more than likely that curl isn't much more than 9 mm or so.

I think she's doing this as a box mold and the mold is trapping glass. If this were an annealing issue she'd have a crack across the face, more than likely through the thickest part of the glass, the nose. That's why I suggested hand building and keeping the mold as thin as possible. The "evenity" should be for the mold material, and an inch of R&R910 throughout is probably more than enough.
Last edited by Morganica on Sun Dec 01, 2013 1:08 pm, edited 1 time in total.
Cynthia Morgan
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Re: Pate de verre cracking

Postby Brad Walker » Sun Dec 01, 2013 1:07 pm

Another comment. Making the mold from a softer material than R&R910 (like 1 1/2 to 2 parts silica, one part plaster) would give you a mold that's a lot more forgiving and less likely to create this kind of problem, even in a box shape. And you don't need the strength for this little amount of glass.

Morganica
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Re: Pate de verre cracking

Postby Morganica » Sun Dec 01, 2013 1:16 pm

Tom Fuhrman wrote:Is that photo of one of your pate de verre pieces, if so,
It is tremendous, both technically and as artistic expression. Love it.
What's the size of it?

Uhm, if you're talking about mine, thank you. That's May II, did her a few years ago, and from the top of the head to the neck wattles she's about 16" long. She's an Alzheimer's patient I met who was furious one minute, lost and bewildered the next. This is the furious side.
Cynthia Morgan
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http://www.morganica.com/bloggery
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"I wrote, therefore I was." (me)

Barb R
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Location: Ft. Collins, CO

Re: Pate de verre cracking

Postby Barb R » Sun Dec 01, 2013 4:54 pm

Kevin,

I read Graham's book and he referred to Lundstrom in his firing schedules. I bought Lundstron's Glass Casting and Mold Making book, and Dan Fenton's Pate de Verre book and was using all of these for reference in doing this, as well as the Bullseye annealling schedules.

Cynthia is right - the glass is only 1/4 to 3/8" thick - it might be a little thicker in the nose - she is hollow. What Cynthia and Brad are saying makes a ton of sense and I will try again with just a silica/plaster mix and see what happens. I probably will add to her hair too.

Cynthia - that piece is incredible. My piece is based on a a mask that was given to me, so not much flexibility in changing the face, but I can readjust her hair. I'm going to glue freeze/fuse flowers in her hair and call her my flower child. I've learned a ton while doing this, and am sure there will continue to be challenges as I move to more fun pieces, but I"m glad I tried this. I have much more admiration for people like you who can do this so well!!

Thanks all.

Barb


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