Help With a Piece Breaking

[glaswizz]

Hello All,

I was hoping someone could help me out with a problem I'm having. My mom wanted me to make her some little thinks to stick in her garden. I was just going to do simple little flower type things, kind of like Spectrum's "Spirit Flakes" that they have on their site. I took two triangles, one small one large, of sys96 for the spokes and full fused them together. I used 2 1" squares fused to make center circles. I was pretty much just using them as filler for my kiln while I was fusing other pieces.

For the second firing I placed them like I wanted and tack fused, using the center circle to hold everything together. I ran one of them. When it was done I took it out and while washing it off the spokes snapped right off. Took me a minute, but judging by where it broke I guessed it was an annealing problem. My schedule was not adjusted for the extra thickness. So I worked out a new schedule thinking it would work great. Not so much. The same thing happened. They keep breaking in the same place. That's why I'm here. Here is the second schedule that I used. I thought it was pretty conservative, but maybe not?

400-1250-20
AFAP-960-105
50-700-OFF

Any tips on what I should change as far as annealing? Any help is much appreciated.

[JestersBaubles]

What's your goal with that top temp of 1250? That's just under my slumping temp. I would go at least another 100 degrees hotter for tack-fusing.

You might find this useful: http://system96.com/Pages/FiringGuideF.html

Dana

[glaswizz]

Thanks for the reply. The 1250 with the hold did tack them together. Maybe not enough? The problem wasn't that they came loose, but that they actually snapped right in half. That's why I thought it was annealing, because it's right where the 2 pieces meet. That leads me to more questions. Would the fact that they weren't "more" tack fused lead to it breaking? I suppose it is possible my kiln temp reading is off. But when I turn it on first thing in the morning the readout says 70 degrees, just like the rest of the room.

[Stephen Richard]

I think you would get better results if you put all the unfused pieces in the kiln in their final configuration and took to rounded fuse. Then they would be properly fused together, especially if the central pieces overlapped the petals. Your kiln may be different, but as Dana says, it appears to be merely a high temperature slump for my kiln. 760ºC would be a tack fuse in my kiln (804 a full fuse)

Second, as Morganica frequently points out to people, tack fusing requires much more careful annealing than full fusing. You have tapering pieces which she notes are among the most difficult to adequately anneal. She has said that such shapes require annealing schedules for several times the thickest part of the piece. Your piece is 12mm (4 layers) thick so might require a schedule for 24mm or even more. If so, your annealing schedule is approximately 4 times faster than would be indicated by simple thickness.

Another reason why I would fire to a higher temperature to ensure the petals are firmly incorporated into the central portion. Then a an anneal such as indicated on the Bullseye chart for annealing thick slabs (http://www.bullseyeglass.com/images/sto ... _slabs.pdf) which goes all the way to room temperature.

The piece is always going to be delicate at the part where the thin glass exits the thick, round centre.

[glaswizz]

Thank you Stephen. I will try doing it differently and making some adjustments to the schedule. I really appreciate everyone's help!

[Eryc F.]

[quote="glaswizz"]

AFAP-960-105

If you're using Spectrum - your annealing temp should be 950.

[Morganica]

I agree, it was an annealing problem, most likely. The most critical join would be where the circle and petal tack together, so it's reasonable that they broke there. Stephen's already done the Morganica-broken-record bit but yep, you're doing a difficult tackfuse, with multiple components coming into a relatively small area while largely maintaining the original profile of the glass.

Each of those pieces will be trying to contract in on itself during cooling, so not only do you need to anneal-soak for a prolonged time (I'd start this at 3x the thickness, or 36mm actually), you will also need to do the slow cooldown for a 36mm thick piece of glass--you can't just soak a long time, drop 50dph to 700 and then shut down--unless your kiln is superinsulated, you'll still be cooling too fast.

However, as he also mentioned, the different components have small areas of attachment which must support a relatively large mass of glass out at the ends of the petal. Even when correctly annealed they'll be fragile, and it won't take much to break off a petal or two. If these are outside pieces, and your mom lives in an area that goes through freeze/thaw cycles in winter, water/ice trapped in the petal interstices could expand enough to crack the glass.

Unless there's a really good reason that the design requires a tack-fuse, I agree with Stephen--fuse these as flat and rounded as possible for maximum strength. Or enlarge the center of the flower to increase the surface area of the petal-to-center join. Or both. And I would avoid as much as possible creating a perfect wedge shape that comes to a point between petals if there's a chance of trapping ice there.