Why did I get holes???

Kathie Karancz · Post by **Kathie Karancz** » Tue Jun 24, 2003 11:56 am

Hey everybody out there: I put a project into my kiln last night - 11"x11" square Spectrum piece with lots of smaller pieces on top for the design so there shouldn't have been any bubbles (this is for a bowl that I have made at least 20 times already with no problems). Full fused and this morning, I opened up the kiln, and I have 2 holes inside the square. One around 2" in diameter and one around 1" in diameter. The holes go right through to the kiln shelf. What the heck happened???
Kathie from Calgary[/b]

Candy Kahn · Post by **Candy Kahn** » Tue Jun 24, 2003 12:07 pm

You didn't mention how thick your bottom piece was. If it was only a single sheet (1/8) then you didn't have enough pieces on top to make an overall 1/4 inch piece. Glass tries to go to 1/4 inch and will pull everywhere to get there and if there is not enough glass - holes.

candy

Kathie Karancz · Post by **Kathie Karancz** » Tue Jun 24, 2003 12:12 pm

Nope, don't think, that's it.... cuz I used a single sheet of Spectrum on the bottom and then covered the entire top with glass (squares and strips of glass side by side) making it the 1/4". I am thinking that there must have been something on the kiln shelf trapping air, but it sure looked fine to me when I put the glass on top. Now that I think about it - the kiln shelf is new to me..... could that be it??
Thanks Kathie

Cynthia · Post by **Cynthia** » Tue Jun 24, 2003 12:55 pm

Kathie Karancz wrote: Nope, don't think, that's it.... cuz I used a single sheet of Spectrum on the bottom and then covered the entire top with glass (squares and strips of glass side by side) making it the 1/4". I am thinking that there must have been something on the kiln shelf trapping air, but it sure looked fine to me when I put the glass on top. Now that I think about it - the kiln shelf is new to me..... could that be it??
Thanks Kathie

Yep. Check to see if the shelf is flat or if it has any depressions by using a straight edge and laying it across the surface of the shelf. If you see dips...you have a depression in the shelf that traps air and will bubble up under some circumstances.

Lots of ways to address this problem. Flip the shelf over and see if the other side is workable and flat, or use fiber paper or thinfire, or use chads to elevate the glass above the shelf, or slow down your firing, or baffle your work from side elements and finally...replace the shelf.

Kathie Karancz · Post by **Kathie Karancz** » Tue Jun 24, 2003 1:04 pm

dang..... maybe this lesson that was learned was - don't buy used stuff from other people.... if may be cheaper, but I just lost $35.00 in glass..... (oh well, instead of bowl, it may just be a funky window piece with beads in the middle of the holes.... hmmmmmmmm.....)
Thanks for your help
Kathie

Bob · Post by **Bob** » Tue Jun 24, 2003 1:21 pm

Hi Kathie,

Place the glass on a flat surface. Does it lie flush against the surface, or does it rock slightly when you push down on one side? If it doesn't lie flat then it may suggest that your shelf had warped at fusing temperature.

I have noticed this with one of my rogue shelves. The shelf elastically returns to it's original "flattish" shape when it cools, but the glass (12" square) was warped enough to rock about 1/4" from corner to corner. It was all compatible glass so I thought that the shelf must have changed shape.

Ask Ken for his money back (heh heh)

Cheers,

Bob