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Just a little history:

I had an attempted combing that wasn't completed so I decided to use it as a design element.

Bottom layer clear; next black opal; the failed combing and design elements to tie in with the failed combing. All glass was System 96. I fired this according my trusted firing program but at about 1100 I peeked in the viewing window and noticed a small crack in the failed combing piece. At this point I just shut the kiln off, figuring it's no good.

After the piece cooled I decided the small crack could be covered easily and still keep the design consistent. So I placed the glass back in the kiln, but this time lowered my starting segment to 200 dph to 1000. At about 800 I looked in the viewing window and the whole piece had exploded.

All that to ask this: Did this happen because I did not anneal the glass in the first firing?

This was the only logical reason to me.

Judy

Judy Schnabel wrote:...All that to ask this: Did this happen because I did not anneal the glass in the first firing?

This was the only logical reason to me.

Judy

Probably. If the internal stresses weren't removed or reduced through annealing then it will be very suseptible to breaking apart once heat is added. The other thing is that thermal shock in my kiln usually occurs at around the lower strain point...somewhere in that 700 degree range. I expect this is typical.

This initial crack you saw was probably also an annealing problem. When you comb glass you are introducing stress anyway, so with all those colors and all that manipulation, you need to add some time to your anneling cycle and slow it down.

Thanks, Cynthia.

When I first looked at the mess I was dumbfounded.

After I had a good night's sleep, I figured it had to be an annealing problem.

Judy

Bizarre as it may seem, 200dph may also have been too fast on your ramp up, if there were huge color contrasts in the piece. I found that out the very hard way...

Barbara

Barbara,

The colors were green, white, blue & black -- all opal.

Would I never be able to use just the black fused to the clear in pattern bars or anything else?

Judy

I'm not quite sure what you are asking Judy.

I agree with Cynthia that not having annealed was probably a big factor in your explosion. But the strong contrasts in your piece between black and white are an invitation to thermal shock even when it is annealed.

What I found was that with pieces that had some colors and whites capped in clear and framed in black, the contrast in temperature between the colors and the black (remember how light colors reflect heat and dark colors absorb it?) while they were heating up, was enough for a thermal shock. It didn't always happen, but it did happen enough times for me to learn that if I had fused those colors together and fired them after they were fused, I had to ramp up more slowly than 200dph to avoid thermal shock. I can still fuse them together, just have to be a patient tortoise (very much against my nature) rather than the speeding hare.

You can use all the colors all together if you wish, and you can fuse black and white together. You just have to go slow and plan for the variance in viscosity and speed of heat absorption between/among your colors.

Barbara

even still, black and white together can give a problem. i made this:



as one of my first fusing projects.

the first time i used it over a tea light, it exploded, even though the candle was about 4" underneath it.

Charlie, do you think that was thermal shock or annealing? Annealing breaks can happen long after a project comes out of the kiln.....

And have you done any more black and white projects?

barbara

Barbara Muth wrote:Charlie, do you think that was thermal shock or annealing? Annealing breaks can happen long after a project comes out of the kiln.....

And have you done any more black and white projects?

barbara

i believe this was thermal shock. since it was early in my fusing, i was over-enthusiastic in my annealing times. i've since learned better how to adjust firing schedules since then, and only blow up pieces rarely.

the shape of it certainly led to a propensity for shock, since the bottom center and the top edges were about 2.5" apart, and were receiving a large heat differential. i've used the shards of this in other projects and have had no bad affects in those projects, but i broke it up until no piece was over about 1" in diameter.

this object didn't break until i heated it over a flame.

Judy Schnabel wrote:Just a little history:

I had an attempted combing that wasn't completed so I decided to use it as a design element.

Bottom layer clear; next black opal; the failed combing and design elements to tie in with the failed combing. All glass was System 96. I fired this according my trusted firing program but at about 1100 I peeked in the viewing window and noticed a small crack in the failed combing piece. At this point I just shut the kiln off, figuring it's no good.

After the piece cooled I decided the small crack could be covered easily and still keep the design consistent. So I placed the glass back in the kiln, but this time lowered my starting segment to 200 dph to 1000. At about 800 I looked in the viewing window and the whole piece had exploded.

All that to ask this: Did this happen because I did not anneal the glass in the first firing?

This was the only logical reason to me.

Judy

If U got side elements U might try

Baffle n Go tm next time

Brian