Help with crack

[Chris Lowry]

So I had a piece crack and I'm a little confused.

I was putting pieces together that were previously fused together. It seems like it cracked on the way up as the crack was partially fused back together. Strange that it wasn't totally fused back together as the parts I was putting together were fully fused.

My question is n schedule... How fast would you go up to temp? The piece was in total 16" x 16" about 1 centimeter thick or .39". I went up at 200 degrees an hour which is what I usually do. Is that too fast?

I'm sure it would be easier to post a picture... I'll have to learn how to do that.

[Peter Angel]

200 degrees F or C?

[Chris Lowry]

200 f

I'm trying to refire the pice right now and I did 150 f an hour.

[Kevin Midgley]

Yes!
The bigger the piece, the more care required on fire up and annealing.

[Chris Lowry]

Well I understand the principle but can never get a clear answer on what is good.

I can find all sorts of schedules for annealing but none for the turn up.

[Kevin Midgley]

read Graham Stone's firing schedules for glass for answers and understanding.
Suggest reading it 3 times cover to cover.
DO not under any circumstances just go to the schedules without reading ALL of the book and its notes.
Then you will realize the schedules that looked so good initially upon first opening the book may not be so good for your kiln and firing conditions.
You will at that point have the understanding to make schedules that work for you.
You also should not be asking at that point for help with cracks.

[Chris Lowry]

I've been thinking about you response for awhile now and although I understand your point of view I disagree with it.

We have so many books and publications out there that we could spend our whole lives just reading and never have any personal interactions. I personally am not the best reader or writer and tend to learn things threw experimenting and personal interactions. Using forums and message boards are a great way to extend my community and have experiences outside of books. Although kind of funny that it is still written word.

It seems like it bugs you that I'm asking for help from other glass workers. If so it seems like forums are not really the place for you. Personally I love them, although I don't participate too often they are a great place to learn. I have read Grahm's book but I still have trouble translating the information to the problems I'm having.

Thanks anyway and have a great day.

[Marty]

Well I understand the principle but can never get a clear answer on what is good.

I can find all sorts of schedules for annealing but none for the turn up.

Chris- My students want schedules- all I can give is guidelines; no one can give you the recipe for your work in your kiln (and what has "always" worked for you in the past may not be a constant).
If you're going up at 200dph and you're getting cracks then maybe you need to try 100dph. Or 50. Or more insulation or a different shelf or separator or kiln.

Please realize that some of us dinosaurs here have been answering the same questions for a very long time and occasionally we get frustrated (or just stop answering).
You said "I personally am not the best reader or writer and tend to learn things threw(sic) experimenting and personal interactions". Your better option might be to find an instructor with whom you can work and take a class (or hire that person for a day's solo instruction which might be a more efficient use of your time and money).

Also remember that these forums are free and voluntary and some of us try to make a living (sort-of) from teaching.

[Kevin Midgley]

As Marty says, the students always want formulas. In fused glass there are no standard formulas. There is no standard bake a cake recipe.
I've had over 20 kilns and currently have 10. Every one of them have different schedules for even similar items being made.
Keep notes, observe.
Every time I fire kilns I observe and learn
Stone just gets you started on the learning path if you read the whole thing and don't just go to the schedules

Bullseye changed its generic schedules for annealing some time ago
I didn't change mine.
They work for me.

[Chris Lowry]

Totally understand what you guys are saying and apriciate the comments. I've been a glass blower for 30 years now but kiln work is very new to me.

I was just frustrated with a piece that cracked when I've had similar pieces that worked great. It makes me wonder if the ones that have worked are stressed or if the new one was just that much different.

Let me ask you this... Do you find that color shapes and patterns effect the outcome as well? The piece that cracked had a big black band that went threw the piece. It cracked at a right angle in the pattern. Made me think of working with cement and how it always cracks at right angles.

[Kevin Midgley]

Working with kiln formed glass ought to renew your brain cells after doing all that glass blowing.
What you could do and get away with as a blower does not necessarily translate directly.
You have begun a new learning curve.

If glass did not 'fit' completely, you could encase it with more glass and hold it together.
This warm glass stuff is not so forgiving.

As for the black, there's regular and stiff which has been noted to sometimes cause 'things to happen'.
My guess is that you don't know which kind of black it was and if you should have treated/fired it differently.
Learning about its differences on the Bullseye site or searching here may provide clues.
There's also the heat absorbancy capability of the different colours with stiff black being obviously slower to move with heat.

My favorite line is 'Speed Kills'.
My kilns are considered under powered.
However they make good glass pieces and rarely do I run into problems such as you have described.

[JestersBaubles]

A picture would help.

You mention a black band, but you don't mention what other colors of glass. Also, how large is your kiln? If the 16x16" piece is close to the walls of the kiln near a heating element, then yes, you might need to slow things down. As it was a fused piece of glass, some of the outcome might depend upon your previous schedule -- especially the annealing.

With no picture of the piece, no indication of the type of kiln, no report of previous firing schedules, no real information at all except it "cracked"... anything that anyone proposes is pure SWAG and is likely not to be very helpful in resolving the issue.

Good luck and I hope you figure it out.

Dana W.

[Chris Lowry]

Well yes so far kiln glass is very temperamental compared to blown glass. It's crazy how after changing one little thing you get such a different result. It is a lot of work figuring out every nuance of the kiln. Just yesterday I thought I should slump at a lower temp since my piece seemed to be done early. Although I didn't think about how that would effect the sandblasted surface and it's finally finish. Piece slumped well but the surface still looks to rough. At least you can just refire.

Thanks for more ideas about why things crack... I know there are a lot of them. Maybe it was kind of a stupid question. I guess what I really needed to know is 200f an hour out of the question for something 1/2" thick or is that still on the maybe side? Or are there just too many variables to answer that.

[Chris Lowry]

image.jpeg (49.62 KiB) Viewed 24260 times

This was the piece

[Marty]

Your initial fuse of strips can be fast- 300dph- with a serious bubble squeeze around 1100.
Subsequent firings of a piece like that shouldn't be any faster than 100dph (up to 1000F) because of the thickness and the black part. Every time I think I can get away with a faster firing I am reminded that I can't.

[Valerie Adams]

Chris, don't be too quick to dismiss Marty and Kevin's advice; you're getting attention from some of the best out there (for free!).

I've been fusing for 16 years; I've got five kilns and do this full time. Patience was never my strong suit; in the beginning I thought most schedules seemed ridiculously slow and conservative, until I blew a few bubbles through pieces.

While I own Graham Stone's book (and bought it when it cost a fortune due to being out of print), I've yet to follow Kevin's advice and read it. Started once, became bored, and set it aside. I do plan to read it one day (maybe even three times ). But in the meantime, I've got a binder for each kiln. I write down all variables and describe the piece I'm firing. Then I record the firing schedule as well as the outcome. Nothing is left out (fired on the shelf? On Thinfire? On thicker fiber material? Kiln carved? Inclusions? etc.). Those binders have become my guidebooks. Even then, as my kilns have aged, I find schedules need to be tweaked a bit sometimes.

So, keep good notes, be much more conservative than you think you need to be, and enjoy yourself.