De-stressing tempered glass.

[J. Savina]

We have recently acquired several pieces of 18" square 1/4" thick glass that was used for displays at an old gift shop. All this glass is tempered. I would like to take these pieces into the kiln to de-stress it so we can cut it and fuse with it and also to do some deep carvings. Would anyone know the best way this can be done, if it can be done. I would like to try to ramp up at 500 degrees/hr until it gets to 1100 and hold for 30 minutes, then maybe ramp up (same rate) till around 1500 for 10 minutes, than ramp down fast to anneal at 1100 for 30 minutes to 1 hour. What can I expect to happen if I try this J.

[charlie]

you need to ramp up slower, and you only need to go to 1100, wait a bit, and then anneal. there's no need to go to full fusing temps.

[J. Savina]

you need to ramp up slower, and you only need to go to 1100, wait a bit, and then anneal. there's no need to go to full fusing temps.

Thank you Charlie. Would ramping at 250/hr be slow enough J.

[charlie]

probably, but ymmv. if it breaks, my advice is only as good as the amount you paid for it.

[Bert Weiss]

We have recently acquired several pieces of 18" square 1/4" thick glass that was used for displays at an old gift shop. All this glass is tempered. I would like to take these pieces into the kiln to de-stress it so we can cut it and fuse with it and also to do some deep carvings. Would anyone know the best way this can be done, if it can be done. I would like to try to ramp up at 500 degrees/hr until it gets to 1100 and hold for 30 minutes, then maybe ramp up (same rate) till around 1500 for 10 minutes, than ramp down fast to anneal at 1100 for 30 minutes to 1 hour. What can I expect to happen if I try this J.

I'll disagree with Charlie. I bet that you can ramp up very fast. tempered glass is much more resistant to heat shock than annealed glass. (unless you are using a side fired kiln at which point I have no clue how fast you can go.) I ramp annealed glass up at 600º/hr and I feel that is conservative in my kiln. I could probably double that and be good as long as the glass is well bedded.

They will not do any annealing at 1100º. That is the slump temp. I anneal at 1000. Others start around 1030 and ramp down. It doesn't take long to anneal 1/4".

I don't like to work up at 1500º any more. I get my work done between 1365 and 1420. Soak longer at lower temp and get brighter smoother castings.

[lohman]

I also aquired a large quantity of tempered glass shelves from a department store. My sheets are 20" x 48". I stack six sheets with a light dusting of diatamaceous earth/plaster mix dry. I sift it very lightly through a fine mesh screen between each layer. Ramp up to 960 F at 10 degrees/ minute (600 degrees/ hour) Hold 1 hour then let the kiln cool at its natural rate.
Have gotten very good results. Glass treated this way cuts like regular glass from the factory. Hint: Wrap some of the tempered glass in several layers of paper. Shatter with a hammer and fuse a layer of this shattered glass on your newly de-tempered glass. I'll try to post a piece built this way on my photo album.

<http://photos.yahoo.com/eugenelohman> look under "seafan"

[ellen abbott]

Why bother? 1/4 annealed glass is cheap. You'll probably spend more money in electricity and time than you would just buying new annealed glass that won't have scratches in it.

e

[lohman]

Why bother? 1/4 annealed glass is cheap. You'll probably spend more money in electricity and time than you would just buying new annealed glass that won't have scratches in it.

e

This reply probably qualifies as a new subject: economics.

Yes, Ellen, 1/4" float glass is cheap. So is electricity, really, when you think about it. In my view not all studio activity is about money. I buy new glass when the project calls for it. This salvaged glass is really recycling. Recycled glass might have scratches but enamels, glazes and frits are just fine for transforming old glass into new art. Many of my clients ask if the glass is recycled before they even discuss the aesthectics. I recycle when I can.

[lohman]

Why bother? 1/4 annealed glass is cheap. You'll probably spend more money in electricity and time than you would just buying new annealed glass that won't have scratches in it.

e

This reply probably qualifies as a new subject: economics.

Yes, Ellen, 1/4" float glass is cheap. So is electricity, really, when you think about it. In my view not all studio activity is about money. I buy new glass when the project calls for it. This salvaged glass is really recycling. Recycled glass might have scratches but enamels, glazes and frits are just fine for transforming old glass into new art. Many of my clients ask if the glass is recycled before they even discuss the aesthectics. I recycle when I can.

[ellen abbott]

I get the whole recycling thing and it's supposed to create less trash and pollution. And if that's the purpose, go for it. There are other ways to recycle however (and I am an avid recycler). I just think that perhaps there is a better use for an artist's time and air polluting energy than destressing tempered glass. Yes, I know it's not all about the money. It's about a quality product. If I did a deep carving on used glass that was scratched (don't know if their used display glass is scratched, perhaps not, but most I have seen is), I know my customer's wouldn't be very happy.

BTW...according to Ceramic Industry magazine, 6.4 billion square feet of flat (float) glass was shipped in 2002 for an estimated value of $2.1 billion dollars. That's about 33 cents a square foot. Granted at the manufacturer's level.

e

[rosanna gusler]

i got started using float because it was cheap (read free). now i just really love to work with it. it is interesting to note peoples response to the whole recycling thing. i have had people indicate that it somehow "justifies" their purchase of a "thing". by "thing" i mean something that they do not really need. alot of folks (myself included) have trouble buying "things". you know, ' but, what is it for?' or 'but what does it do?' or 'why do i need that?'. we have folks in our booth glancing and looking and when we say that all of our glass is recycled they start to fondle and buy. weird but true. rosanna

[charlie]

Why bother? 1/4 annealed glass is cheap. You'll probably spend more money in electricity and time than you would just buying new annealed glass that won't have scratches in it.

e

This reply probably qualifies as a new subject: economics.

Yes, Ellen, 1/4" float glass is cheap. So is electricity, really, when you think about it. In my view not all studio activity is about money. I buy new glass when the project calls for it. This salvaged glass is really recycling. Recycled glass might have scratches but enamels, glazes and frits are just fine for transforming old glass into new art. Many of my clients ask if the glass is recycled before they even discuss the aesthectics. I recycle when I can.

what happens when you tell them it causes more pollution to recycle the glass than buying new?

personally, i'd use the old glass in something, like skylights, tabletops, or windows, rather than untempering it.

[jerry flanary]

One cool thing to do is to stack three pieces together and tape around the edge. Then use a spring type punch on the edge of the middle piece so that it shatters. Then fuse them all together! Amaze your friends!

[Bert Weiss]

One cool thing to do is to stack three pieces together and tape around the edge. Then use a spring type punch on the edge of the middle piece so that it shatters. Then fuse them all together! Amaze your friends!

Jerry

The middle piece needs to be tempered or heat strengthened. To get a better break pattern, drill a tiny hole in the center of the bottom sheet. The break will radiate from the hole instead of from the edge.