Uneven slumping and draping usually happens with a smaller kiln, more than one item in it, and is affected by placement of the pieces in the kiln. If an item is not in the center, the edge closest to the side of the kiln, and therefore closest to the side elements, will get more heat, so that glass will soften and move before the rest of the piece. If you are slumping or draping more than one item at a time, you are more likely to have problems of this type unless you have a large enough kiln to allow good placement of all articles. Slower ramp up rates, lower slumping temps, and longer hold times can lessen the problem. Big thing is – don’t overload the kiln.
Keep really good notes/logs describing placement – even drawing diagrams or taking a photo (digital cams are great!), glass used, and the firing schedule – review your notes and comments – that is the best way to learn when and why something is happening in your kiln.
Hope this helps, and
Fused Glass, Wood, Beads, PMC, Ceramics
Usable and Wearable Art
Art for the Sake of Art