Same Glass - and it cracked when fused

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kbarbour
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Same Glass - and it cracked when fused

Post by kbarbour »

Wondering what would cause the same glass to crack when fused together? I did several peices with high temp wire running all the way through the middle. The glass that I used was not tested, but I thought that if I was fusing it together it should be ok. Every peice broke. I was using an irridescent glass and that all burned off?
Stuart Clayman
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Post by Stuart Clayman »

What type of glass was it? Was the crack along the wire? Did both pieces layers crack? Did it crack on the way up or the way down? ie was the crack partially healed? Do you have pictures?
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kbarbour
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Post by kbarbour »

I'm sorry I don't have a picture, but both the top and bottom were cracked on each piece all over. I didn't see a pattern along the wire. Most of them were still in tack but the entire top and bottom were cracked into tiny pieces. In fact, when I set them down I could still hear them "ting". I am pretty new to fusing and didn't understand what you meant by "were the cracks partially healed". I also don't know what type of glass it was. The piece was from my stained glass stock. I knew better, but I have had some luck fusing together other glass to itself that had not been tested and I hadn't seen this before.

Karon
Geri Comstock
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Post by Geri Comstock »

What brand of glass was it that you used? Some glass isn't compatible with itself, believe it or not.

As for being healed, if the edges of the crack are rounded and seem to be flowing together, it means the glass cracked on the way up to your top temp. If the edges are sharp, it means the glass cracked while it was cooling. When the glass cracked makes a big difference in diagnosing problems. Did you anneal the glass? What temp did you anneal at?

Geri
kbarbour
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Post by kbarbour »

Thanks for the great information. I'm learning so much, and have so much to learn. I let the kiln get up to 1500 degrees and then I flash vented down to about 1100. Because the pieces were so small I let them cool naturally overnight.

Karon

P.S. This is a wonderful site for information, and everyone is so generous with their help. Thanks a bunch!!!!
Geri Comstock
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Post by Geri Comstock »

First of all, there's no need to flash vent unless you're in a hurry.

Secondly, when you put metal inclusions in glass, you're probably going to have to anneal the glass so that it doesn't crack.

Do you know annealing is?

Geri
kbarbour
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Location: Michigan

Post by kbarbour »

I always thought you were supposed to flash vent to stop the process of fusing. Thanks!

My understanding of annealing is it's the process of letting the glass cool slowly and evenly for a period of time at a controlled temperature? This portion of fusing does somewhat confuse me. Should I have annealed at a particular temperature and held it for a period of time even with pieces so small? Please let me know if I'm totally off base.

Karon
Cynthia

Post by Cynthia »

kbarbour wrote:I always thought you were supposed to flash vent to stop the process of fusing. Thanks!

My understanding of annealing is it's the process of letting the glass cool slowly and evenly for a period of time at a controlled temperature? This portion of fusing does somewhat confuse me. Should I have annealed at a particular temperature and held it for a period of time even with pieces so small? Please let me know if I'm totally off base.

Karon
Flashing can also get you out of the devit zone, and for art glasses you will be experiencing more devit than with fusible glasses...If you can use an overglaze to inhibit devit you will be better off than with flashing. It's hard on the brick and possibly the elements to flash vent not to mention the arm hair you singe and sleeves you can melt. :shock:

Glass has an upper and lower strain point which is measured at tempurature and indicates the annealing zone of a particular glass. For different glasses that zone will be different.

To anneal 90 coe glass you want to hold at a temp that hovers above the upper strain point and Bullseye gives that hold temp as 960F for their fusible glasses. You hold at that temp according to the size and thickness of your piece in order to allow it to come to an equal temp throughout the body of the piece. The surface will naturally cool more rapidly than the core and the shrinkage will cause stresses between these differently cooling areas within the glass. Annealing decreases these levels of stess by cooling at a rate that is more equalized throughout the body of the piece. Once you have allowed the temp to equalize at above that upper strain point you then want to cool it at a rate slow enough to allow an even temp to be maintained throughout the body of glass as you cool to below the lower strain point. For 90 coe glass that is somewhere around 750F.

Your annealing schedule should be adapted to meet the volume of glass you are cooling. For small jewery sized pieces of glass, the annealing process is often successfully accomplished simply by allowing your kiln to cool naturally. The rate is slow enough for the glass to keep up with the cooling rate within the kiln. For larger pieces, say getting closer to 6 inches in diameter, and particularly if it is thicker than the standard 1/4" will require you to hold at the upper strain point and then do a controlled descent to below the lower strain point in order to anneal you piece properly.

You need to know what the annealing range for the glass you used is in order to anneal it properly, as well as what the times, temps and rates at which to cool the glass is appropriate for the size of your piece.

I don't know what the strain points are for art glasses, but if you can tell us what glass you are using, someone might very well know what those temps are and could tell you.

After all of that...I think the glass you used is just not going to work. It sounds as if there is so much stress there that it speaks of incompatibility to me more so than an anneling issue if indeed these pieces are as small as cabochons....That is if you allowed your kiln to cool naturally after your initial flash venting...and if the pieces are jewelry sized smallish.

One more question....What kind of wire were you using and at what guage?
kbarbour
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Post by kbarbour »

Hi Cynthia, again thanks for all the info (and I thought I knew what I was doing - Yikes)! I was using 24-guage high temp stamen wire.

Karon
Cynthia

Post by Cynthia »

24 guage is pretty skinny, so I sincerely doubt that it is creating your trouble...I'll stick with my original hunch.

Keep playing. You'll learn and learn and learn through all the successes and particularly through the failures...even when it's crazy making. #-o
Lynne Chappell
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Post by Lynne Chappell »

Well, I have had some trouble with hi-temp wire. It seems ok if you make a loop and stick the two ends in, but something I did that had wire across it broke. Can't exactly remember the circumstances.

If the glass is still tinking and breaking as you were taking it out of the kiln then it certainly sounds like an annealing failure. Since you're not sure what kind of glass it was, you could just cool it slowly from 1000 to 900 (should cover most types), over maybe a couple of hours. You said the iridescence burned off. Sort of says Spectrum glass to me. Spectrum will almost always fuse to itself successfully. There are some types of glass from the other stained glass manufacturers that give a lot of trouble though.

Maybe you should try the same layout with the wire with some glass that you have used successfully before , and conversely try the glass that broke without the wire and try to isolate the problem.
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