It's Always About the 1/4 Inch - Glass 101

Each of the 3 layers of this pendant (not including the freeform stringer,) began as rectangular pieces.  That really means that the top half of the piece is two layers and the bottom half, with the orange "oreo filling" is three layers.

3 layer pendant using scrap - pre-fired

As you look at the shape of the piece after it is fired, below, you probably noticed that the overall shape is no longer rectangular, but irregular. 

3 layer pendant using scrap - post firing

This goes back to the glass rule:  molten glass flows to 1/4 inch in thickness.  If you think about the volume of glass by dividing the top and bottom half of the pendant, there is 1/3 more glass in the bottom than in the top.  Two pieces of 3mm glass, layered one on top of the other, full fuse to just about 1/4 inch.  Adding a third piece of 3mm glass, in this case, lets say it is the orange piece on the bottom half, the glass, when molten, is now about 5/8 of an inch thick - NOT allowed in the world of glass.

If this piece were dammed to keep the glass from flowing, the shape would have remained rectangular, but the bottom half would be thicker than the top half.  Since no dam was created to restrict the glass flow, in the kiln, the hot glass continued to flow until the 1/4 inch rule was achieved.  The color of the glass does not seem to impact this rule, but some coatings seem to have some effect.

For example, the iridescent coatings are frequently on black glass.  The glass portion follow the 1/4 rule, but the irid coating seems to seek the smallest surface and frequently pulls and puckers toward the center of the irid section.  The opalescents seem to react the same way as the irids.  I have observed pieces where the irid and opalescent coatings appear to crack and draw toward pockets on the surface - these have been larger pieces.  I imagine this has as much to do with the speed of heating to the highest temperature, the length of time the glass "sits" at the high temperature, and it could also be connected to the speed of cooling.