Cracked during heat up - WarmGlass.com

Cracked during heat up

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Sandy Pendleton
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Joined: Thu Jul 12, 2012 11:42 pm

Cracked during heat up

Postby Sandy Pendleton » Wed Aug 05, 2020 7:35 pm

I need some advice… I had high hopes for this piece, but it cracked on the way up during a polish. The edges of the break were rounded and partially fused back together. Hopefully I have successfully attached the photo. It had a combed center and pattern bar sides. I’d like to try it again, but I’d like to avoid another break. The piece is 16” x 16”, all 96 glass, but by Spectrum, Oceanside and Uroboros. This firing was on a corelite shelf with no dams. The piece has some variation in thickness, 3/8” to 5/16. There is no sign that the glass stuck to the shelf, and no sign of problems during the previous firing. No sign of operational problems in the kiln. Below is my firing schedule. The previous firing had the same annealing schedule except the last segment was 100 to 300. Thank you for your help!
60 300 H10
60 800 H10
60 1050 H10
200 1390 H 10
9999 960 H4 hrs
9999 850 H 2 hrs
80 300

Thanks, Sandy

Brad Walker
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Location: North Carolina, USA
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Re: Cracked during heat up

Postby Brad Walker » Wed Aug 05, 2020 9:30 pm

Can't see a photo. Try attaching again, if you can't get that to work, email me the photo and I'll put it up. Email is wg at warmglass.com

Sandy Pendleton
Posts: 16
Joined: Thu Jul 12, 2012 11:42 pm

Re: Cracked during heat up

Postby Sandy Pendleton » Wed Aug 05, 2020 10:12 pm

cracked small.jpg
this is the photo

Michael Stevens
Posts: 67
Joined: Thu Dec 26, 2019 2:52 pm

Re: Cracked during heat up

Postby Michael Stevens » Thu Aug 06, 2020 2:14 am

well looking at your schedule seems slow enough. I usually allow more time when have glass with different qualities, opaque and transparent. if you have lots of bubbles in the glass, or thick and thin fused Together.

I vent my kiln little bit on heatup to 500c that always reduces thermal shock in. my kiln. but if I made bubble glass or other sensitive piece it's not easy.

the look of the crack doesn't seem to be incompatible between different companies glass.

Sandy Pendleton
Posts: 16
Joined: Thu Jul 12, 2012 11:42 pm

Re: Cracked during heat up

Postby Sandy Pendleton » Fri Aug 07, 2020 3:16 pm

Thank you for the reply. I don't understand the relationship between venting the kiln and reduced thermal shock. Can you explain?

Michael Stevens
Posts: 67
Joined: Thu Dec 26, 2019 2:52 pm

Re: Cracked during heat up

Postby Michael Stevens » Fri Aug 07, 2020 8:03 pm

my kiln heats up too quick. even if I set it at 5 hours to get to 550c, still can thernal shock some pieces.

Sandy Pendleton
Posts: 16
Joined: Thu Jul 12, 2012 11:42 pm

Re: Cracked during heat up

Postby Sandy Pendleton » Fri Aug 07, 2020 8:17 pm

Ah, thank you.

Sandy Pendleton
Posts: 16
Joined: Thu Jul 12, 2012 11:42 pm

Re: Cracked during heat up

Postby Sandy Pendleton » Fri Aug 07, 2020 8:48 pm

Maybe the real question I have is about reheating a combed piece. I use Patty Gray's combing schedule that has a 4hour hold at 960 and a 2 hour hold at 850 and then slowly down from there. I then add the side pieces and reheat with the firing schedule in my first entry. My question is: When reheating the combed piece, is it enough to ramp up slowly, or do I need to add some long holds at key times? Would that produce less stress? Thank you for your help.

jim simmons
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Location: Hillsboro Oregon
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Re: Cracked during heat up

Postby jim simmons » Sat Aug 08, 2020 1:07 pm

It does look to me that it is an incompatibly problem.
Maybe some of the glass shifted in the combing cycle.
I have had that happen to me before.
There is a lot more than COE involved in the heating process.
I suggest that you stick to the same manufacturer.
I also suggest that you read the BE article on COE vs compatibility.
The other Jim

Sandy Pendleton
Posts: 16
Joined: Thu Jul 12, 2012 11:42 pm

Re: Cracked during heat up

Postby Sandy Pendleton » Sat Aug 08, 2020 2:24 pm

Jim,
Thank you for your response. I have suspected this might be an incompatibility problem, but I don't know how to tell for sure. I thought maybe the break would follow the color boundary. I have read the BE article. I have done lots of combings over the years with 96 glasses, but this is the first time I have included Oceanside white. It looks denser than the old Spectrum white, and perhaps it is stiffer. I haven't heard this is a problem in 96 land, but I am suspicious.
Thanks for your help,
Sandy

Dick
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Location: San Diego
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Re: Cracked during heat up

Postby Dick » Sun Aug 16, 2020 6:43 pm

I think the coe changed as well. That and the Oceanside glasses are different in some ways than the Uroboros

Sharol
Posts: 117
Joined: Sun Mar 05, 2006 2:45 pm
Location: Tennessee

Re: Cracked during heat up

Postby Sharol » Tue Aug 18, 2020 4:26 pm

I understand you observed the piece cracked on the way up, but I would think too about the anneal cool segment you’ve used. I think 9999 from 960 to 850 is too fast, especially with a piece involving multiple firings. You may be retaining stress with each firing. I’ve done a lot of combings with white glasses, which present challenges, especially with multiple firings and when combined with transparent glasses. An adequately slow anneal cool segment is Important.

Sandy Pendleton
Posts: 16
Joined: Thu Jul 12, 2012 11:42 pm

Re: Cracked during heat up

Postby Sandy Pendleton » Tue Aug 18, 2020 4:42 pm

Thank you for responding, I so appreciate the help. I can slow it down from 960 to 850, but how much? Would you mind sharing your annealing schedule? Do you think my ramp up schedule is appropriate for multiple firings? I would think that cool down on subsequent firings would need to be as slow as the first combing.
Thanks, Sandy

Sharol
Posts: 117
Joined: Sun Mar 05, 2006 2:45 pm
Location: Tennessee

Re: Cracked during heat up

Postby Sharol » Wed Aug 19, 2020 9:30 am

I always hesitate to publish my schedules for high fire and challenging compositions, because my experience/kiln is unique to my work. Still, I think once you eliminate the compatibility questions, I believe slowing your anneal cool segment would be helpful.

If I was adjusting your schedule, I would slow the cooling segment after the 960 hold 50 dph and take it all the way down to 800, eliminating the hold at 850. Then I would cool at 100 dph and turn off the kiln at whatever temperature you are comfortable leaving your kiln to cool on its own.

Hope this helps. PM me if you’d like.

Good luck! I know how frustrating it can be trying to diagnose these types of problems.

Sharol

Sandy Pendleton
Posts: 16
Joined: Thu Jul 12, 2012 11:42 pm

Re: Cracked during heat up

Postby Sandy Pendleton » Wed Aug 19, 2020 9:50 am

Thank you for the help. I am going to adjust accordingly and try again.

Sharol
Posts: 117
Joined: Sun Mar 05, 2006 2:45 pm
Location: Tennessee

Re: Cracked during heat up

Postby Sharol » Wed Aug 19, 2020 10:31 am

It’s a beautiful design and you've obviously put a lot of time and thought into it. I hope you post photoss of it when it's completed. :)


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