CaN A PIECE BREAK BECAUSE OF BAD ANNEALING???

[Havi]

I guess it can.
Can it be fixed in this case?

What should I do? Refire to full fusing and sit for how long?

A piece on which I had been working for quite a long time - looked ok when I peeped [I should not have done so..... I know. 'speed come from the devil! ]

And broke once I took it out of the kiln.

It is NOT thermal shock. I can see the signs. It might be compatibility, but recently I realized that the piece is not on even thickness. So it might be that I did not anneal properly..... I am ashamed to admit.

If so - then I can correct it, can't I???

Please do not ask me to post a photo................

Please respond,
I'd be more than grateful

Havi

[Brad Walker]

Yes, a piece can break because of bad annealing.

What does the crack look like? Curved? Straight? Side to side? Is it in one piece or two?

What firing schedule did you use? Please describe the piece's size and thickness and variation in thickness. And at what temperature you peeked!

[Havi]

PHOTOS

Thanks Brad
Here are photos
of the breaK
of the cracks on the back side, But then why are the cracks where they are???
on the front side [ very hard to see them, even in reality
The violet was BE 1234, the 'green' is definitely incompatible.
Basically the schedule was very conservative, as in reality the violet looked black and I worried about thermal shock because of it.
The difference in thickness in not big, 1 or 2 millimeters.
here is my schedule in centigrade [my apologies....]
50 - 250 -10
50 - 540 - 10
333 - 670 - 30
9999 - 515 - 45
50 400 5
99 250 2

Thanks for your comments

[Bert Weiss]

Stress is stress, regardless of where it comes from. Stress is cumulative, so adding a little bit more can cause a crack. If you have compatibility stress, combined with annealing stress, and you add a puff of cold air to it, your result is not a surprise.

Many years ago, I was trying to cut the thinnest strips possible from a sheet of Bullseye streaky green opalescent. I found I could do this consistently in a place in the sheet where there was just the opal base. The glass would break on me in the streaky places. I called Bullseye to ask why. I learned a lot from this little experience. They told me to look at the edge where the streaks were and what I saw were deep striations emanating from the score. In the places where the sheet was consistent, there where no striations. These striations were caused by stress from the compatibility differences between the 2 glasses. We know that 2 glasses can live together within a range of compatibility stresses, without breaking. If you get towards the outside of that range, you will get effects.

I just saw the picture and it looks like a combo of annealing and thermal shock to me. There is no trace around an offending color, which indicates incompatibility.

[Kevin Midgley]

Read Graham Stone's Firing Schedules for Glass.

[Brad Walker]

Photo 1 looks like annealing to me. I don't think 45 minutes is long enough hold at 515C/960F.

[Kevin Midgley]

it isn't enough to just find a schedule somewhere, including on Bullseye's charts and in Graham Stone's book (instead of reading the whole book). You have to understand what you are doing to do it correctly.

[Havi]

Thank you All for your responses.
As usual I learn from it a lot.

It is definitely bad annealing.

The piece is still in the kiln, but it is one piece, not two. Looks to me OK .
I am glad I thought it might be bad annealing. It did not look thermal shock, and the cracks at the back of the piece did not look compatibility problem.

Another lesson learnt

Havi

[DonMcClennen]

You did not say at what temp. you opened the kiln and peeked. This can undo all the anneal depending where it occurred!

[Havi]

BAD NEWS!!!!
I can't believe it, it broke again! almost parallel to the previous break.

I'll post a photo later.
That's it. I am giving up.


Thank you all.
@Don, I do not remember at what temp. I opened the kiln. sorry. I admit that I usually do it, and nothing breaks...

Havi