Bubble Squeeze

What it does:

Reduces number and size of bubbles both between the layers of glass and between the glass and the kiln shelf.  This stage also prepares glass for more even fusing.  Here is an example of the firing schedule step required for a Bubble Squeeze phase:

Firing Schedule - Bubble Squeeze

Things to consider:

Glass is heavy.  By spending extra time in the slumping range, the weight of the glass will help the glass layers settle together, squeezing out air that might otherwise be trapped between them or between the glass and the shelf.  With less trapped air, bubbles become smaller and occur less frequently.

Here are some reasons to consider lengthening the Bubble Squeeze:

  • The glass has an uneven surface that creates places for air to get captured.
  • Your project includes wide pieces of glass where escaping air has a long distance to travel to escape.
  • You’ve been having problems with large bubbles bursting through the surface of you work.

A typical bubble squeeze might be only 30 minutes long.  An extreme bubble squeeze can last two hours or more.  Keep in mind that fused glass is rarely completely free of bubbles.

A lesser known bubble squeeze benefit:

In addition to minimizing trapped air, there’s another benefit to holding your glass at 1225° F: Glass will melt more evenly when it fuses together.  Why?  While glass is a great insulator when solid, as it softens it changes into an increasingly good conductor.  Glass molecules that “loosen up” during the bubble squeeze allow the heat required for fusing to move more easily – and thus more evenly – in the steps that follow.

Fire Polish schedule

I have fused a piece of glass for a plate, however, I think it shifted so the edge was jagged.  Also one of the staples that holds the heating element in the kiln fell onto the edge of the glass.  I have ground this down to be fairly even but now I was told to fire polish the piece before slumping.  I can not find a schedule for this.  Could someone help me please?

Carleen Gates


This is fire-polishing: it's done between 1300 and 1400*F, so higher than simply slumping. So, it should be done the polish on the plate before to slump it.

Hi, firepolishing is taking

Hi, firepolishing is taking the glass to the softening temperature of the type of glass you are using and the thickness of the piece. Typically heatng to the slumping temp and holding briefly (I eyeball the piece when slump temp is achieved) until the edges have rounded. So, in answer to your query, it's not necessary to re-fuse your piece prior to slumping.

I have a Lifelong Passion For Glass

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