large piece glass cracking issue

[ironman55]

I need some advice. I fired this, and before it was done I turned it off , I think too soon. I turned it back on but too late.
It cracked really bad. (Like the days when you boiled a marble and put it in cold water to make it crack on purpose.)

Anyway, I re-fired it the next day, but this time I did not mess with the program and I actually slowed down the cooling segments.
It cracked the same exactly. Could it be the shape? Is there any way to save a piece that has cracked? The second time I fired it I took it up to 1600F

I am fairly new to this, This is my 6th firing. None of my other pieces (All square) cracked.

This piece is also raked. I woke up this morning and remembered an article I read about the compatibility of opal glass vs transparent. This is all Bullseye 96coe. SO I have clear 3m tekta-black-opals-transparents-some striker- glass drops spectrum 96 frits and powders hmmm too many ingredients?? ugh!

Any help would be deeply appreciated. Thanks, Joe

[Kevin Midgley]

COE's are different. Can't mix 96 and 90.
The others may not have cracked yet. May still do in a year's time if you have mixed the two COE's together.

[Valerie Adams]

You've got a few things going on here!

First of all, you say you're using 'Bullseye 96 coe' which doesn't exist. Bullseye Glass is considered 'tested compatible', meaning it works with their entire line of fusible glass. Bullseye does not use a coe number associated with their glass, although many glassworkers tend to refer to Bullseye as 90 coe.

If you've combined Bullseye with Spectrum 96 frits and powders as you stated in your last paragraph, that could be your biggest error. Bullseye and Spectrum are two different glasses and not to be used together.

Next, when you fire glass to extreme temperatures, and especially multiple times, it can sometimes lose it's compatibility, even with glass by the same manufacturer. I've heard reds and yellows are especially susceptible.

And the shape of your piece, with those 90° angles, is enough to cause extra stress at the corners. A piece like this would require extra care in the firing schedule, especially in the annealing range.

It would help if you'd post your entire schedule but first, I'd double check that you haven't actually used two different glasses in this piece.

[Morganica]

Whoa...as Val says, it's probably time to dial things back a bit and take this step by step. Glass fusing looks simple but there are a LOT of variables. When you're starting out, and want to try a lot of different ideas at once, it can be tough to figure out exactly what's going wrong.

First thing you should do is take a very good class in basic kilnforming, if possible from a good glass center. Not sure where you are, but if you can let us know we can recommend a few places. I'd also suggest getting one or two books on kilnforming basics. Brad Walker (the owner of this website) has an excellent one, available from this site or from Amazon. Brenda Griffith does another, A beginner's guide to kilnformed glass, available on Amazon. Bullseye also has a series of excellent tutorial videos for $35/year which may be the best bargain yet. Any of those will provide a lot of information on what may be going on with your glass.

For now, I agree with everything Val and Kevin are saying. Most likely, if you're combining Spectrum 96 and Bullseye glasses in any form and getting cracking, you've got a "compatibility" problem. Those glasses expand and contract and move at different rates during firing, and they will literally break away from each other. If they don't crack (or even explode) during firing, the stresses set up as the glasses freeze in place are often enough to cause cracking later, when even a little heat is applied.

There's no way to fix a compatibility cracking problem unless you completely remelt the glasses back into "batch" (i.e., around 2400F) and start over. But then it's no longer compatible fusing glass and you won't have your design--it's all one piece of glass in one color. Likewise, as Val says, if you overfire your glass its compatibility starts to shift, so you could be compounding your Spectrum/Bullseye issue with shifted compatibilities. Six firings where some are over 1600F, especially with warm colors, could be enough to do it. In general, keep fusing glass schedules under 1500F, apply as little heat in as few firings as possible to achieve the effect you want.

Boring as it sounds, for your seventh firing you might be better off to pick one or two techniques, use the class/book/video schedules and make a couple of successful pieces and get the whole compatibility/firing schedule thing down.

[ironman55]

Thanks for the help. I thought the bullseye glass was both 96coe and compatible, learning curve I have only used the spectrum glass pebbles and have not had a problem. I do think the shape was a major contributor. I have attached a pic of a different piece that I did and also slumped it and no problems.
I enjoy the look of raking and it needs to be 1600 to get it to move enough when raked.

Ah to learn to learn!

Thanks again for your help!

[Valerie Adams]

Yikes. That 'successful' piece looks fairly thick, which would require a very long anneal.

The thing about incompatibility is that while a piece may not crack, break, or crumble right out of the kiln, it still likely has significant stress, which means it could break sometime later. Especially concerning if you've got that piece somewhere where it could hurt someone.

I had the power go off during a firing once. I brought the piece into the house, since it looked ok. It was sitting on the kitchen counter and I was in the other room when I heard a noise. When I went to investigate, I found shattered glass all over the counter and floor, where the piece had burst apart. I hate to think of what could've happened if a child was standing nearby...

[ironman55]

the piece is only 6mm

[Bert Weiss]

The Spectrum glass nuggets are compatible with about nothing. There was a discussion about this recently, here or somewhere.

[Judd]

Ironman55
" I have only used the spectrum glass pebbles and have not had a problem. I do think the shape was a major contributor."

No dude. Mixing 90 and 96 glass - that was the major contribution to the destruction of your glass. You can't mix COE - or at least don't try it until you know how to fuse glass.

[Jerrwel]

Thanks for the help. I thought the bullseye glass was both 96coe and compatible, learning curve I have only used the spectrum glass pebbles and have not had a problem. I do think the shape was a major contributor. I have attached a pic of a different piece that I did and also slumped it and no problems.
I enjoy the look of raking and it needs to be 1600 to get it to move enough when raked.

Ah to learn to learn!

Thanks again for your help!

Congratulations for jumping into fusing with both feet (figuratively). There's more to be learned from things that don't work than those that do although it can get discouraging. Here's a response on another post where I listed good resources:

"Another topic...books...there are lots and lots of books about lots and lots of topics. To get started and get your feet on the ground I suggest, Contemporary Fused Glass http://www.warmglass.com/cfg/ by Brad Walker of Warmglass; great step-by-step 'how to' with many projects each building on the topics learned in preceding projects. This one is heavy on in-depth understanding of glass and heat; The Kiln Companion (Firing Schedules for Glass) by Graham Stone http://www.warmglass.org/books/books/126-fsg. Don't even think of reading Stone until you've finished Walker. One of my favorites for ideas and variety is Joy of Fusing by Randy and Carole Wardell; good overview of process temperatures for various effects and purposes. This book also has a couple of examples of using a single layer of glass as the base for a project - great for using non-tested glass.

One of the best ways to distinguish your work from others' is coldworking. Get good info from Coldworking Glass without Machines by Paul Tarlow http://www.hisglassworks.com/cart/Coldw ... _p855.html. The book is listed at the HIS website; these folks know all there is to know about coldworking. Just a hint - I do most of my coldworking in my primary or secondary steps and not so much on the finished product; saves oodles of time and effort. There are many discussions of coldworking on Warmglass.com. Consider coldworking a late starting or medium level fusing activity."

The suggestion to take a basic class is good but making the projects as presented in 'Contemporary Fused Glass' is a great substitute and it requires close reading of the book so that important information is not missed. Also, since it appears you have both 90 and 96 COE, separate them carefully so that they don't get mixed in the future. I use only one COE to avoid that issue entirely.

The shape of your project is indeed an issue for future reference. Stone's 'The Kiln Companion (Firing Schedules for Glass)' addresses design variations that introduce additional stress into projects (right angles is one of them) and how to compensate for that stress.

[Brad Walker]

This is all Bullseye 96coe. SO I have clear 3m tekta-black-opals-transparents-some striker- glass drops spectrum 96 frits and powders hmmm too many ingredients?? ugh!

Bullseye doesn't make a 96 COE glass. So if you mixed Bullseye glass with any Spectrum you will surely get incompatibility problems and cracking.

[Morganica]

Thanks for the help. I thought the bullseye glass was both 96coe and compatible, learning curve I have only used the spectrum glass pebbles and have not had a problem. I do think the shape was a major contributor. I have attached a pic of a different piece that I did and also slumped it and no problems.
I enjoy the look of raking and it needs to be 1600 to get it to move enough when raked.

Ah to learn to learn!

Thanks again for your help!

Well, shape *is* a contributor to annealing problems. Lots of things are: Right angles are a lot more difficult to anneal than soft curves. Acute angles are more difficult than obtuse angles. Asymmetric shapes are (much) more difficult than symmetric. Round is much easier than cubic.

However, except in rare cases those issues can be resolved by adjusting the firing schedule. No amount of schedule adjusting (that I'm aware of) will fix a compatibility problem. That's why everyone is focusing on the 90 vs 96 stuff. The other issues are important, but nothing matters until the glass is compatible.

I like the look of raked glass, too, but you must be aware that--especially with warm-colored glasses such as reds and yellows--the heat required to rake the glass may also shift its compatibility, especially if you're using previously fired scraps.