Avoiding Bubbles with Mica Sheets

Fused multicolor leaves

Fusing glass is great fun, until you open the kiln and find gigantic bubbles!  There are some tricks to avoid having bubbles in your glass, particularly when fusing with inclusions like shapes cut from mica sheets.  Let’s get started.

  1.  Make sure your mica is as thin as possible.  It is an inclusion, after all, so it is going to hold the layers of glass apart no matter what.  By reducing the thickness as much as possible, you reduce the amount of air trapped.  I like to use a thin, long, razor blade to slide between the mica layers (carefully).

2.  Create a path for air to escape.  I like to do this by adding a center layer of glass and cutting it into sections.  These cut lines act as conduits for air to escape.  Here are some examples of the center layer with cut lines.  Another way to accomplish this is to add tiny grains of glass or frit between the layers, as they fuse into your project, they will allow the air to escape.

3.  Adjust your firing schedule.  By slowing down the ramp rates and adding a hold in the slumping range, you can accomplish a ‘bubble squeeze’ and encourage the air to escape as the glass fuses.  Here is an adjusted fusing schedule for example:

Ramp Rate (F) Hold Temp (F) Hold Time
300/hr 500 15 min
250 1300 10 min – 40 min
Bubble Squeeze Hold
200 1550 8 min
9999/hr 1060 45 min
50/hr 940 0
100/hr 740 0
off to room temp

This is a sample firing schedule for float glass, it WILL NEED TO BE TESTED AND ADJUSTED!  There are many variables that will effect your firing success, including glass thickness, inclusion thickness, kiln size, etc.  I’m always happy to help with adjustments, give this schedule a try, then send me photos via the contact form and I can offer suggestions.

Related Articles:

Fusing with Sheet Mica Tips and Tricks

Fusing with Metal Inclusions

Fusing with Dirt and Sand Inclusions

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