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pieced dish splits during slumping fire

Posted: Fri Nov 13, 2015 4:06 pm
by conboc
The fusing firing looked ok. During he slump firing the dish split apart pretty much along the seam of the top glass. I used two 3mm layers of COE 90 glass.
The slump firing schedule was:
250 to 350 soak for 12 min
350 to 750 soak for 22 min
FULL to 1400 soak for 15 min
FULL to 900 soak for 1 hr.
100 to 70 soak 1 min.

Re: pieced dish splits during slumping fire

Posted: Fri Nov 13, 2015 5:02 pm
by Marty
Too fast. Too hot.
Please tell us where you got that schedule.

Re: pieced dish splits during slumping fire

Posted: Fri Nov 13, 2015 7:25 pm
by David Jenkins
What do you mean by "seam" of the top glass - was it two pieces that you fused together? Also: In the picture, it looks like the bottom was of two colors - is that correct? Or is the black-looking right hand side just an artifact of the camera shot?

Re: pieced dish splits during slumping fire

Posted: Sat Nov 14, 2015 8:45 am
by conboc
Marty,

I can’t find where I got that schedule now. I either took it off the metallic decal instructions, or I made a huge mistake when I copied whatever schedule I was looking at. It certainly isn’t the bullseye one for slumping. I do have to fire a bit hot in my small kiln to get full fuses, I had one decal flake off, so I bumped up the heat a bit for the high fire metallic decal.

David,

Yes, it is 4 pieces of glass: two on top, two on the bottom and the seam for both layers was in the same place. Was that stupid maybe?

I really, really appreciate you fellows help, as I there is no place near me to take classes.

Re: pieced dish splits during slumping fire

Posted: Sat Nov 14, 2015 11:51 am
by David Jenkins
I would think that the markedly different colors would require an especially slow schedule, since the two colors absorb heat at significantly different rates. That would cause undue stress to occur at the joint line.

Re: pieced dish splits during slumping fire

Posted: Sat Nov 14, 2015 2:10 pm
by Jerrwel
conboc wrote:as there is no place near me to take classes.


Classes are not a panacea; they are typically fun and some good information is available. Growing to understand the interplay of design, glass and firing processes is essential. Several books present keys to successful glass fusing well. Brad's 'Contemporary Fused Glass' http://www.warmglass.org/books goes through steps actively providing understanding of various fusing process basics; the Wardells' book, 'Joy of Fusing' focuses on some easy projects using different processes and not requiring a full fuse on all of the projects. Both books look at the understanding and development of firing schedules so that one does not need to blindly trust a schedule provided. The eventual advanced step is to read, read, read, and use 'Firing Schedules for Glass' by Graham Stone; a single read is not sufficient and understanding the variables within glass and glass projects (such as glass elements within a project absorbing heat at differing rates) presented in this book is essential to becoming independent in designing and executing fusing projects. While information regarding a particular glass or design element is needed, Stone's book helps one integrate that information with knowledge of other project variables to determine what is likely to be a successful firing schedule.

There are several axioms that are true to fusing; here are two, (1) 'low and slow,' and (2) 'more is learned from failure than success.' 'Hurry up and wait' schedules containing numerous holds during firing stages are contrary to the 'low and slow' mantra and I avoid them. Painfully accept that failure is part of learning and learning never stops.

Re: pieced dish splits during slumping fire

Posted: Sat Nov 14, 2015 8:38 pm
by conboc
thank you for your help.
Appreciate the book recommendations.

Re: pieced dish splits during slumping fire

Posted: Sun Nov 15, 2015 7:48 pm
by Valerie Adams
conboc wrote:Yes, it is 4 pieces of glass: two on top, two on the bottom and the seam for both layers was in the same place. Was that stupid maybe?


I wouldn't go so far as to use the word stupid, but there's no need for the top layer to be two pieces, especially since you're placing a decal on top. The top layer could've just been a single piece of clear which would also help to hold the two bottom pieces together, assuming a successful first firing.

Re: pieced dish splits during slumping fire

Posted: Sun Nov 22, 2015 8:22 pm
by conboc
thanks Val,
I've made two more dishes and used a solid piece of clear for the top, and yes, that is working fine. I am realizing that design choices need to be tempered with practicality, at least for a beginner.

And I am SO thankful for the earlier suggestion to get Brad Walkers book! It is WONDERFUL. It contains so much useful information all in one place. its clear, concise an deasy to understand. Even things I already know something about are so much more clear now. What a wonderful find. I can't put it down.