Approaching Pattern Bars

Glass has a few interesting properties.  One of them is that when molten, it will flow to a thickness of 1/4 inch.  If a platter, for example, has one spot that is thicker than 1/4" because of creator embellishments, that spot will flow to 1/4 inch and deform the edge of the platter - which will also be 1/4 inch thick. 

Full fused layers of 2mm glass as a result of damming.

There are a couple of ways "around" this.  One of them is to "tack fuse" your piece instead of "full fuse."  Tack fusing means that when fired, the temperature inside the kiln gets hot enough to begin to melt the glass.  Pieces of glass touching one another will bond to form a unified surface, thus "tacking" them together.  While edges of glass will round slightly, exterior edges do not fully round and edges of layered glass remain elevated.  The glass does not become fluid and level out to 1/4".   Areas that are a depth greater than 1/4 inch are determined by the designer and not by the kiln.

Full fused layers of 2mm glass as a result of damming.

Another way "around" the 1/4" property rule is to limit the space in which the molten glass is able to flow.  Just like with water in a river, this is called "damming."

Full fused layers of 2mm glass as a result of damming.  Notice that a portion of one layer is NOT clear.

By constructing a defined and confined space in which to place the "cold-worked" glass, the shape of the final produce is limited only by the boundaries created.  Not as easy as it sounds when the temperature inside the kiln is raised to a level that turns the glass molten (1500+ degrees F), but a means to a "greater than 1/4 inch end," when done successfully. 

Full fused layers of 2mm glass as a result of damming.

 

At the current time, it seems as though the majority of the time, pre-existing kiln posts and shelves are being re-purposed to create small dams.  I have recently seen a mold designed to result in a thicker end-produce.  Until now, the only molds I have seen resulting in a 1/2" to 3/4" product were small and designed for pendant jewelry.  These ovals, "donuts," and hearts would span a diameter of 1 to 2 1/2 inches.  The growing interest in glass creations with actual depth, complex patterns, and variations in thickness appear to be driving creative " work-arounds."