help ?Fusing Blue flaot glass ? RIDDLE ????? explosion

[Sandy Jackson]

I am using blue 2000 to fuse/cast a 1 and 1/2" Ctop. I am using 6 sheets of 1/4 " as that was all that was available . I first did a 32 x 96 " long piece that came out perfectly. Then I did a 32 x 54 and it basically exploded. It looks as if the 2nd layer sheet just blew out. I checked the kiln and one of my relays was out , so I replaced it and fired again. This pieces also blew up $$$$$$$.
Now, I did use some kiln blanket 1/4" in all 4 corners to keep a "space" between to help keep bubbles out. I have found that this allows the center to sink in first and press more air out. My first thought was that on the smaller piece there was a greater pressure point in the center ??????
I am using the same schedule that I do for regular float glass. The large firing came out perfectly, why did;nt the smaller one ? twice , the same explosion. Should I slow the ramp up time down for this dark glass. Any help would be great.
I can only get my hands on enough blue glass for one more try and its a piece that goies in a kitchen with the larger piece. CRAP !!!!!! now I am very nervous. I am including 2 images of the back side of the glass in case that give a "clue" as to what happened. The white stuff is just sand.


Sandy

[Sandy Jackson]

[attachment=0]blowup2.jpg[/attachment][attachment=1]blowup.jpg[/attachment]

[Valerie Adams]

I can't offer any suggestions as to what's gone wrong but I can tell you that in order to receive help, you need to post your entire firing schedule.

[Rick Wilton]

I cannot see how the smaller size should pose a problem that the larger didn't. Are you sure the relay was the problem and that it is now in fact fixed? Have you fired anything else since the "fix"

[Sandy Jackson]

The theory with the smaller piece was because I had 6 layers stacked with 1/4 " fiber in the corners between each layer which caused it to bow a bit more dramatically than the larger piece. I had wondered if it put too much pressure on the center of the bottom piece in more of a concentrated point
Perhaps the 96" piece had more contact space. I also decided to slow the ramp up and take the spacers out just in case the lower piece was not heating up equally and the top layers softened first and then put heat and pressure on a single point in the middle.
Does that make any sense ?
I'm going to test fire tomorrow before I attempt the expensive stuff again, but all electrical contacts have equal current, unless my controllers gone bad, but it fused and annealed everything very well after the "blow up" so I'm thinking it happened on the ramp up ????
ANY THOUGHTS OR COMMENTS

[rosanna gusler]

schedule? kiln configuration? i do know that in my big kiln that the sand under the glass heats first. i can see where the larger size could have 'seen' heat more evenly. slowing way down beloe about 1100f never hurts. rosanna

[Bert Weiss]

Sandy The explosion seems to be happening because the edges are a very different temperature than the center. I can't imagine that pressure from weight has any effect on the breakage. I would not do anything to the corners. Just do a very conservative bubble squeeze.

Your problem appears to be caused during the heatup. Go a lot slower. It can only cost you some time. Since it worked once, you might not be too far off, but there are hundreds of postings here that say, "my schedule always worked before, why did this one break?" In my work with broken tempered, I had to slow way down to stop a few bowls from cracking during a firing with 10 bowls in the kiln.

There is a big problem using 6 layers of 6mm. The top layer is quite light weight, so bubbles tend to form under it. Then you have a big thick mass of glass with a 6mm thick piece on top. This creates an annealing challenge, as the glass above the bubble wants to cool quickly. Hence a really conservative bubble squeeze.

Rosanna's statement about the sand heating first is true with clear glass. I think the blue tint may be entirely different as the IR heat is seen more readily by the tinted glass than clear glass.

[Sandy Jackson]

Excellent , I didn't even think about the sand issue, Thanks all, I'll slow it WAY down.

[rosanna gusler]

slowing down is like chicken soup for a cold....'does it work? dunno, it cant hurt' rosanna

[Bert Weiss]

slowing down is like chicken soup for a cold....'does it work? dunno, it cant hurt' rosanna

Slowing down will solve the problem. The question is how slow? I was loading my kiln with 10 bowl molds with fused broken tempered discs, set on them. 6 would slump fine and 4 would crack. I had to slow down a lot more than I thought I would have to, before 10 came out intact.