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Minimize Curved Edges When Slumping a Deep Square

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I stumbled upon this idea when I got carried away constructing this strip cut bowl. I had chosen my deep slumping mold before I got started. While I was in the throes of placing the hundreds of strips, I decided to add a nonexistent border to my design on the fly. Of course, that was never factored in to the size constraint of the largest square mold I had. After fusing, I went to place the piece on the mold, and DUH! Way too big! OH NO! WHAT TO DO? Well, I didn't want to saw off my border, so I did a brain scramble to find a way to use the mold to get the thing slumped. Here's what I did, and the result I stumbled upon was a fix for an old problem.

After the mold was already placed in the kiln, I constructed a 'flush platform' around the perimeter of the mold. This serves to begin to hold the edges of the glass in place as the middle starts to slump in. When it's time for the edges to follow, they lift off the platform and move into the mold. The result is a larger piece that fills the mold, and exhibits much less of that curved in or draped distortion on the edges.

​Place your mold on kiln posts or any other kiln furniture to raise it off the floor of the kiln for good air flow. For this slump, I used 5” kiln posts bridged using Bullseye dams which are ⅝” deep.

This left me with ⅛” below the rim of my mold. I use fiber paper, in this case ⅛”, to make the bridge flush with the top of the mold and to give the glass a cushion to lift off of.

If your measurements are different, adjust your fiber by layering 1/16” and or ⅛” fiber so that your construct is flush with the top of your mold. Set this up as tightly as you can. Then cover all the fiber paper with thinfire. This facilitates the the glass to slide off the bridge and into your mold. The bowl above was approximately 1” bigger than the mold, or ½” all the way around. The glass itself was ⅜” thick. This mold is a 16 ⅞” square. The glass is the same from corner to corner! I can't say what the limit is as far as size difference. Always test!

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  • This was very helpful. I have ran into this problem before and I just trimmed the piece I had worked so hard on. Thank you!

    Pam on

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