What Happened, and Can I Fix It? - WarmGlass.com

What Happened, and Can I Fix It?

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Linda Blackburn
Posts: 14
Joined: Thu Jan 24, 2008 11:48 pm
Location: Georgia

What Happened, and Can I Fix It?

Postby Linda Blackburn » Fri Sep 29, 2017 8:18 pm

This was a 11.5" X 1/2" thick pot melt. Everything was fine after the initial pot melt. I cold worked the edges and then fired again to smooth and round the edges. When I opened the kilned after the second firing this is what I found:
download/file.php?mode=view&id=7466
download/file.php?mode=view&id=7465

As. you can see in the closeup, the edges are sharp, so I assume it happened on the way down. Notice the piece that blew off and lodged on the wall. Here are my schedules:

1st Fire, Pot Melt:
Rate Per Hr > Temp > Hold
250 > 1000 > 15 min
250 > 1100 > 15 min
450 > 1700 > 5 min
9999 > 960 > 3 hours
100 > 700 > OFF

2nd Fire, Round and Smooth Edges:
250 > 1050 > 10
60 > 1250 > 30
250 > 1430 > 10
9999 > 960 > 2 hours
100 > 700 > OFF

My questions, again, are: why did this happen and can I fit it all back together and refire?
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Linda Blackburn

"Art flourishes where there is a sense of adventure." - Alfred North Whitehead

Jerrwel
Posts: 129
Joined: Thu Feb 10, 2005 6:25 pm
Location: Charlotte, NC

Re: What Happened, and Can I Fix It?

Postby Jerrwel » Mon Oct 02, 2017 11:31 am

The Bullseye 'thick slab' anneal charthttp://www.bullseyeglass.com/methods-ideas/annealing-thick-slabs.html lists 100/55F as the anneal temps for .5-inch glass; this is probably for a typical, first-firing layup of glass and not glass that has experienced multiple and high temperature firings with many colors (all indicators to use more conservative schedules). Slower annealing was probably needed; the .75-inch anneal rate on the chart is 45/22F which is probably more than conservative enough to avoid the breakage experienced. This is a 'learning' piece at this point, so why not refire and see what results? The Bullseye 1-inch slab firing schedule is probably appropriate now; the cost of properly annealing the project will be a longer firing time.
Jerry

Sharol
Posts: 98
Joined: Sun Mar 05, 2006 2:45 pm
Location: Paradise, CA

Re: What Happened, and Can I Fix It?

Postby Sharol » Mon Oct 02, 2017 12:08 pm

Linda,

What COE glass did you use in the melt? If it is COE 90 or 96, your anneal cool in both firings is way too fast for a 1/2” thick piece, especially one that has been high-temp fired. I would slow that down to 25 to 35 degrees from your anneal soak to 800 degrees and then you could speed up a bit, say to 50 when cooling to 700 degrees. Also, depending upon how cool your shop is, I would control the cooling from 700 to 500 as well rather than just turning your kiln off at 700.

If you decide to re-fire the piece, remember that even if it looks sound, it may still retain stress that could cause it to be unstable if incorporated into another design.

Melts can be difficult creatures! Slow down and Good luck! Y :D
Sharol

Linda Blackburn
Posts: 14
Joined: Thu Jan 24, 2008 11:48 pm
Location: Georgia

Re: What Happened, and Can I Fix It?

Postby Linda Blackburn » Tue Oct 03, 2017 7:25 pm

Thank you both for your answers. It is indeed a learning process! I did try to refuse this and multiple cracks occurred. I've sucessfully fired many 7" pot melts, but this was the first 12". I did another one yesterday and it broke too - on the way down somewhere between 72 and 80 F. I'm firing in a 14" square kiln. My theory is that the small size has something to do with the EPIC FAILS. I joined the Bullseye video lessons and am learning a lot. I will definitely slow down the anneal and anneal cool next time. Since these are pot melts do you think I need to slow down the initial heat stage also. I will be using new glass - not refiring.

Another possibility is that I have been combining Bullseye and Wissmach glass - both COE 90. Is it possible that the Wissmach glass is the problem? It's certainly much cheaper, but maybe you get what you pay for!

By the way, my studio is in my basement and is pretty much 68 degrees F all the time.
Linda Blackburn

"Art flourishes where there is a sense of adventure." - Alfred North Whitehead

Marty
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Joined: Mon Mar 10, 2003 3:58 pm
Location: Maine
Contact:

Re: What Happened, and Can I Fix It?

Postby Marty » Wed Oct 04, 2017 10:21 am

"Another possibility is that I have been combining Bullseye and Wissmach glass - both COE 90."

DON'T.

Jerrwel
Posts: 129
Joined: Thu Feb 10, 2005 6:25 pm
Location: Charlotte, NC

Re: What Happened, and Can I Fix It?

Postby Jerrwel » Thu Oct 05, 2017 6:32 pm

Linda Blackburn wrote:
Another possibility is that I have been combining Bullseye and Wissmach glass - both COE 90. Is it possible that the Wissmach glass is the problem? It's certainly much cheaper, but maybe you get what you pay for!

/
I have used Wissmach without issues and appreciate the price difference tremendously! The only real problem has been consistent devitrification with one of the ambers; this issue may have been solved as I have not obtained any of their glass in over a year. I've had no problem with compatibility. The limited styles of glass available compared to Bullseye is a big factor but using what is available can be gratifying.

I see that Marty recommends not mixing glass from different manufacturers and have read that before.
Jerry

jim simmons
Posts: 409
Joined: Sun Mar 09, 2003 10:37 pm
Location: Hillsboro Oregon
Contact:

Re: What Happened, and Can I Fix It?

Postby jim simmons » Fri Oct 06, 2017 3:12 pm

COE is NOT the only determining factor in determining the compatibility.
The other Jim

Linda Blackburn
Posts: 14
Joined: Thu Jan 24, 2008 11:48 pm
Location: Georgia

Re: What Happened, and Can I Fix It?

Postby Linda Blackburn » Mon Oct 09, 2017 8:43 pm

It's hard to pass up the price difference, especially when you're a beginner and experimenting.
Linda Blackburn

"Art flourishes where there is a sense of adventure." - Alfred North Whitehead

linn keller
Posts: 51
Joined: Mon Mar 10, 2003 12:22 pm
Location: south tx

Re: What Happened, and Can I Fix It?

Postby linn keller » Tue Oct 10, 2017 12:43 pm

hi!
looking at the top pic you posted, it appears the crack runs along a color line. this often reflects incompatibility.
high temps can result in coe changes in some colors, esp. reds, yellows, maybe oranges...
your piece may be suffering from areas of incompatability because you subjected the glass to the temps of a pot melt and the reheat, resulting in more cracks, could well be because there are now multiple coes present.
plus you're mixing be and wasser and, as jim said, compatibility is more than coe.
linn
linn in deep deep south texas


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