WarmGlass.com

I have just completed my first fusing project. It look awesome but when it finished and I put it on the kitchen cabinet, it cracked. After doing more reading on the subject, I determined that it was because of impropper fusing and when I took it out of the kiln, I rinsed it off and cleaned it up. So onto the second attempt. No where in my book did it say that I couldn't simply put the piece back in the kiln and try to fuse it back together, so I did just that. I annealed it slowly and let it stay at 970 for 45 minutes and then 960 for 45 minutes and then I went down one number on my kiln dial per hour till it was off. I also left the piece in the kiln till the next morning. At lunch today, I took my beautiful piece out of the kiln and left it on the kitchen counter. No rinsing! When I came home from work, it was broken. I am so stumped and upset that I want to sell the kiln. My piece is made out of two round layers of Spectrum 96 clear glass and an accent of an "N" of a yellow piece of Spectrum 96. I was told that this was compatible glass. Can anyone offer any advise. Char

Any chance you can post a picture -- or at least describe the breaks?

Did it break the same places the second time as the first?

http://www.the-larkins.com/kiln.htm
Thanks for looking into this. There is a picture at the bottom of the page.
Char

My moneys on annealing/thermal shock (each way bet) ..form your photos I did notice you are using a swinging arm readout gauge..... In those far gone days when I used that type gauge the reject bin was always nearly full with that .....if only it had turned out the way I wanted and hadn't cracked.......then I purchased my CIC 66 stage controller....and have never looked back ..

Colin C/- Spab's world of glass tm

Char,

From the appearance of the break I'd also suspect an annealing problem. However, you might want to run a compatiblity test with a couple of scraps of the same glass just to make sure it is not a compatibility issue.

As your pieces get bigger and thicker, annealing becomes more of a problem. You might want to try a few smaller pieces to get some confidence with this. Write everything down as you experiment.

Make sure your descent from 960 to 700 is slow.

Don't give up. Get something back in the kiln today.

Steve

Just elaborating on Colin's comment, you really have no idea how accurate your pyrometer is... it could easily be 100 degrees off when coming down from a fuse. You should consider getting a digital pyrometer, or at least checking yours with cones (as an estimate of temperature).

Tony

CIC 66 stage controller? Can you direct me to where I would find one on these?

I think it is a compatibility problem. The crack runs down between the two pieces of color then heads for the nearest edge. Any differences between the color and the clear are doubled in a narrow slot like that. If it broke in the same place the second time it must be compatibility. Annealing cracks usually work from the center of the piece, in pretty straight lines, out to the edges.

I can't tell for sure if the clear is above the N, beneath it or both. It looks like it is just beneath. Sometimes a bubble in a narrow spot like that can be enough of a weakness to cause problems. Look closely for a bit of smutz (kiln wash maybe, or other debri) or devitrification caused by grinder dirt along the ends of the legs of the N.

As far as possible pyrometer malfunction - did the temperature at the fusing point look normal? Say 1480 if the design is fused flat or somewhat lower if there is still some relief (it is a little hard to tell from the picture).

Really, you should try another piece. Perhaps you could start your annealing at a little higher temperature (1000F?) just to be on the safe side.

If, as Charlie suspects, it’s a compatibility problem, fuse up a simple chip test, view the glass through polarizing lenses and you’ll know.

If, as many others suspect, it’s annealing, here’s some basic stuff to consider:

More than hitting any specific “correctâ€

Lani's "book" raises some questions I've been puzzling over.

First does everyone or most of you out there own "polarizing lenses" to check on glass compatibility?

I've been using some Uro 90(lime -# 60-703-90) with various BE glass. I like the yellower green of it. Now it sez it's compatible with BE, but I've heard that Uro 90 sometimes really isn't compatible w/ BE.

I'm only making small tiles with it, so if there is stress between the BE & Uro it hasn't shown up yet. Will it show up in larger pieces?

Do I need a polarizing lenses to check this out?

Carla, puzzling

Carla,

(ick, another book.....)

Dunno how many people actually test with polarizing lenses. I’d be curious to know. It’s simple, it’s cheap; if the project is important, why not?

Re Uro 90 and BE compatibility. Here’s what the manufacturers say:

- Uro says their 90 glass is compatible with ours (BE).

- We (Bullseye) say that we’re uncomfortable claiming compatibility with any glass that we ourselves have not tested with our procedures in our facility against our standardized base glass. AND we have insisted (ad nauseum) - and been supported by numerous authorities - that simply having the same COE is NOT assurance of compatibility.

We have simply been in this thing long enough to know that being cautious is usually the best tactic.

Will your small tiles of UB90 & BE have so much stress that they break? Likely not. Should you assume compatibility for larger projects? Why not test to be sure?

Lani

PS. Meanwhile, in over 20 years of doing this we’ve seen MANY more fusing problems that result from poor firing schedules than from incompatibility between glasses.

Lani McGregor wrote:Dunno how many people actually test with polarizing lenses. I’d be curious to know. It’s simple, it’s cheap; if the project is important, why not?

I do. I test when I use non tested compatible stained glass, float, and sometimes Uro with BE.

Although I have a few larger sheets of polarized film, for most testing I use a broken pair of polaroid sunglasses. Total cost: $0.00 -- they were given to me by a local drug store.

http://groups.msn.com/chaniarts/fusedgl ... hotoID=237

Carla wrote:Lani's "book" raises some questions I've been puzzling over.

First does everyone or most of you out there own "polarizing lenses" to check on glass compatibility?

I've been using some Uro 90(lime -# 60-703-90) with various BE glass. I like the yellower green of it. Now it sez it's compatible with BE, but I've heard that Uro 90 sometimes really isn't compatible w/ BE.

I'm only making small tiles with it, so if there is stress between the BE & Uro it hasn't shown up yet. Will it show up in larger pieces?

Do I need a polarizing lenses to check this out?

Carla, puzzling

you can use a pair of cheap sunglass lenses to check polarizing.

i've used uro 90 as a clearcap on platters up to ~22" over bullseye of many different colors without having cracks.

http://groups.msn.com/chaniarts/fusedgl ... hotoID=267

i think this is an annealing problem. i had a similar crack in non-clearcapped large dish that was solved by just decreasing the temp sink rate during the anneal stage.

http://groups.msn.com/chaniarts/fusedgl ... hotoID=237

Lani McGregor wrote:Carla,

(ick, another book.....)

Dunno how many people actually test with polarizing lenses. I’d be curious to know. It’s simple, it’s cheap; if the project is important, why not?

Thanks Lani. That's helpful. Keep writing your "books."

It appears that some sort of polarizing lenses is a good idea. I have a friend who is a fused lamp maker in Portland, who had a minor compatibility problem and the piece broke weeks after it had been installed. No one was hurt, but my concern is, that cracks might show up not in the studio where I can fix things but..... long after the tile has been installed. So, I will check the compatability of this particular color of Uro with my BE glass.

Brad et al........how do you use your cheapie free glasses as a polaring lense. My understanding is that you put the fused glass in question on the polarizing lense and shine a light thru the lens and then the glass. Right? So do you put on the glasses, lay your glass on the glasses, where is the light source come from? I know, I know, another dumb question.

Carla

Carla wrote:Brad et al........how do you use your cheapie free glasses as a polaring lense. My understanding is that you put the fused glass in question on the polarizing lense and shine a light thru the lens and then the glass. Right? So do you put on the glasses, lay your glass on the glasses, where is the light source come from? I know, I know, another dumb question.

You need a base glass. I use clear of a known type. Cut a strip of that glass about 1 1/2" wide and several inches long. (how long depends on how many pieces your are testing)

Cut the test glass in a square, around 1" by 1" or a bit smaller. Cut one test square for each square you are testing.

Place the test glass on top of the base and fuse flat. I usually just put things I want to test on the side of a normal full fuse firing, but you could fire the kiln with just the test if you wanted.

To conduct the test, you simply sandwich the already-fused piece of glass between the two pieces of polarized film (or the sunglass lenses) and hold it over a light source (such as a light table or a flashlight). Rotate the lenses so that they are at right angles to each other and as little light shines through as possible. Now check the edges where the different glasses come together for a white glow. The brightness of this glow will determine the severity of the stress and the degree of incompatibility.

The main limitation of this test is that you must use a transparent glass for the base in order for the light to shine through.

More on compatibility (including a photo) here: http://www.warmglass.com/Glass_compatibility.htm

Brad & Lani:

Thank you! That is exactly the info I needed. I'm fusing some samples and polarize them when done.

Carla

Brad Walker wrote: You need a base glass. I use clear of a known type. Cut a strip of that glass about 1 1/2" wide and several inches long. (how long depends on how many pieces your are testing)

Cut the test glass in a square, around 1" by 1" or a bit smaller. Cut one test square for each square you are testing.

If you are using base strips that are 1-1/2" wide we recommend that you use chips that are no more than 1/2" square. You need to have a good distance between the chip and the edge of the base strip. A 1" square on a 1 1/2" strip only gives you 1/4" distance to the edge.

Most all glass will show annealing stress along its edge. If your test chip is too close to the edge you can mis-read annealing stress as incompatibility stress.

L.

Char,
I am also new to fusing, about 2 years into it...it always gives me new finished projects. I guess I do the hillbily method, which has given me good results about 90% of the time. here's my secret. I Take it to a full fuse, and then vent to about 1100. Then close my kiln and forget about it till the morning. How simple can that be! I have not had any cracks yet. As a college graduate, sorry i misspelled hillbilly!!
I just received my new kiln today, for Mother's Day" It'a a 24" Jen-Ken
The moving people left it outside till I can get some guys to get it into my house! Let me know how it goes! Happy fusing.
Vickie

If you're just going to let your kiln cool naturally, then it would be a good idea to watch it while it is passing through the critical range (1000-800) to see how fast this happens. Lots of brick kilns that take overnight to cool down to room temperature pass through this range way too fast to avoid annealing cracks.

Occasionally, I've not looked at the kiln in time and it's already dropped to say 800. In the past, I've taken it back up to 1000 and started again, but after reading that even cooling is more important than the time at annealing point, the last time that happened, I just left it alone and let it cool naturally. It wasn't a large piece - 11" diameter 1/4" thick. It didn't crack on cooling, but it didn't survive the reheat for the slumping cycle, and probably would have cracked on its own later. This is in a typical brick ceramic kiln. So if your kiln cools faster than 100 degrees per hour in the annealing range, then I think you better turn it back on, uneven heating or not.