Cave Art

[Babette (Shawn)]

I took both of Bob Leatherbarrow's classes last year... I have been planning a HUGE cave art piece ever since. This is 24" by 20" and under 1/4 inch thick. I did not do the full "crackle" here-thinking too many lines would make it too busy. I may have gotten carried away with color...I always do. Unfortunately this piece has some problems, it has some very strange surface cracks. I am working with Bullseye to see if it is a compatibility problem. Has anyone out there had problems with BE opaque white powders?

[Buttercup]

Well done, Babette, you must be thrilled. I've long been fascinated by cave paintings and was lucky enough to visit the caves at Altamira before they were closed to conserve the paintings. Jen.

[JestersBaubles]

Sorry for the problems, but beautiful piece, nonetheless.

Dana

[Barry Kaiser]

Hope the small cracks don't cause a problem. Could be that they actually enhance the texture of the artwork. The piece is too beautiful to lose.
Great use of color!

[twin vision glass]

Oh dear, could you zero in on a section with a photo so we can see the tiny difficult sections. So sad.
(Ps.) how many times did you fire it. What was the kiln shelf. Hmmm! Les

[Babette (Shawn)]

Thanks for the compliments! Here is a close up of the cracks.

The cracks are only on one side of the piece, they do not transfer to the backside (medium amber) YET! The cracks are only on the side with the crackle; French Vanilla powder 20%, Opaque white powder 40%, white opal 40% (all are newly purchase glass) and a slash of marigold, orange, yellow and oregon grey.

The firing schedules are conservative:
1. ramp up to 1000F at 100/hr. hold 30.
2. ramp up to 1250 at 300/hr. hold 1 hour.
3. then 300/hr up to 1500 hold 15.
4. then AFAP to 900 hold 2 hours,
5. 50/hr to 800 no hold,
6. then 100/hr to 400 OFF.

I did not open the kiln, NOT ONCE, until it was at room temperature. When I took the piece out I did not see any cracks but then again I was not looking for them. so I proceeded to cold work and then tack fused the wafers on with the same schedule except I ramped up more slowly. These cracks did not happen in the kiln, the cracks started forming within minutes after I pulled it from the kiln. I tested the medium amber and it is compatable. This firing schedule has worked perfectly in the past 20-30 times! The only thing I can think of that is changed is a new supply of white powders. I even did a second piece and capped with a red transparent glass and it cracked just the same. Then I flipped and fired it to heal the cracks and it cracked again. Shoot me.

[twin vision glass]

I think someone else had this problem a while back. Does anyone remember that. Les

[Babette (Shawn)]

Keep in mind that this piece was fired twice, and the second time was a tack fuse at 1400. The top temperature this piece reached was 1500F. Plus I did a repeat piece and only went up to 1480F, same annealing schedule...then I let it sit for a week after it was completely cooled down, I never lifted the lid to my kiln, not once...and it also cracked the same type of cracks, with just one firing?

[Havi]

Les,
Did you mean ME?
But I went as high as 1700..........
Also there was someone else who comlained that his combings cracked. A bit later than me. I think in his case they suggested that it was an annealing problem.



Hugs,
Havi
I think that in my case, I just stayed too long [45 minutes] at 1700, and this was the culprit for creating incompetability - which caused the cracks. [because, 15 minutes at 1700 did NOT crack, I tried it more than once]

[twin vision glass]

No dear Havi, I thought it was a crackle piece also , but not sure. Les

[Nikki ONeill]

Babette: It sure looks and sounds like incompatibility with white. Nice piece. You could try blast away the cracks if they aren't all the way through, and pumice. Or cut up the piece in sections and re-assemble leaving out the cracked areas.

Nikki

[twin vision glass]

I still think it would be a super idea to take some of the offending glass, put on 1101 30 bullseye, fire with your schedule , and then check under polorized film. You will get your answer. P.S. try upside down on fiber toooo just how you also created the piece.
Les

[Havi]

Babette: It sure looks and sounds like incompatibility with white. Nice piece. You could try blast away the cracks if they aren't all the way through, and pumice. Or cut up the piece in sections and re-assemble leaving out the cracked areas.

Nikki

Good idea,
As well as Leslie's [also good idea


Thanks,
I'll try it on mine, manybe

Havi

[Nikki ONeill]

Babette, you might want to send Bob an email. Maybe he would have some insight. The paleolithic horse I made in his class is as special as the piece you expanded upon to make, and hopefully your piece will find a home on a wall in your house.
Cheers,
Nikki

[Sylvia Simon]

Hi guys haven't visited the board for quite sometime but Babette your piece is wonderful.
I can't comment on the reason for the problem "ohh the bafflement" fusing not being something I do but just a suggestion for 1 of the pieces maybe.
If it is stable enough because as you mentioned the cracks don't go all the way through, if you wanted to perhaps visually improve the look of the cracks on the piece you could try rubbing some black ink into them and perhaps seal by rubbing in some clear glu/laquer. Maybe in some areas slightly open the cracks as fitting for the design. Don't know if you could even use another matching colour like a red.
Because you already have those black random lines as decoration already it may give an interesting effect to the piece, and look as if it is part of the design.
Best of Luck,
Regards
Sylvia

[Babette (Shawn)]

Thank you everyone for the suggestions. I am working on finding out what went wrong but so far it is looking like it is an incompatibility problem. I have been talking with Bullseye and I think they are also running some tests. I just did a new piece with everything the same except no WHITE powders, I substituted opaline for the white powder and the piece is crack free! I will keep you posted because if there is a problem with their formula everyone should be careful how they use white. To be honest it would be better if I did do something wrong, it would we easier to change a schedule than to change my use of white powders...so I'm addicted to white powder am I?

The cracked piece still appears to be stable, the cracks are only on the surface where I used the white powders, they have not transmitted through to the back of the glass. I will keep it as it is, it looks as good as it can but any glass person will see the cracks as a fault and a non glass person might think it was meant to be or just the nature of the material...it kinda looks like the crazing you get on pottery.

[Kevin Midgley]

White is slow to absorb heat. COE is a whole range of factors and while you cooked your glass at high temperature, the white could very well have been considerably cooler /experiencing less of that heatwork. If you had annealed the piece for say twice the time and over a greater range of temperatures than is normally acceptable practise, you might have been able to pull it off without the cracks.
I stress might have been able to.
Another factor in the white thing is that as a powder, the white along with being a heat reflective colour as compared to say black, would also have all the micro air bubbles between the granules further insulating and slowing the heat energy transfer. Visualize the white powder as a block of insulation stuck in the middle of your art work.

If you also fired at lower top temperatures for a longer period of time to equate to the necessary heat work, that might have reduced the high temperature volatization of the trace COE changing chemicals being lost to the air inside the kiln.
Less loss = less COE change.

[Babette (Shawn)]

I got an email response from bullseye today:


"Our technicians have had a chance to look over all of the information related to the cracking in your pieces, and to do some testing with the 0013 powder. They’ve determined that what you’re experiencing is the exact same type of cracks that appear in the 0013 powder when it’s sandwiched between 2 layers of glass-the issue addressed in the warning label on all jars of this powder so people can either avoid or encourage it depending on their goals.

This is the first time we’ve seen the Opaque White powder behave like this when it isn’t between layers of sheet glass but testing showed that you’re building up enough of the powder on the fiber paper to essentially act as another layer of glass, causing the tiny, harmless cracks. These won’t continue to develop or cause residual stress in the final piece.

There was a general consensus that the extra cracking adds another layer of design dimension to the work and that it looks good with your design, but if you want to avoid the cracks you’ll just need to use the 0113 White or other powder. We always recommend running a test before committing to making a large work and strongly suggest doing chip tests whenever mixing powder colors together.

I hope this is helpful! Please let me know if you have more questions and thank you for your patience as we worked on getting you an answer."
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But isn't a crack a CRACK and it means there is something wrong? It sounds like incompatible glass, incompatible with one firing to no higher than F 1500? Plus this cracking is new and just started happening with the recent batch of purchased glass.