Avoiding Bubbles with Mica Sheets

Mica Leaf Coaster Project

Fused multicolor mica leaves – No bubble intervention

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.  Once your mica pieces (in our case leaves) are as thin as they can be, place them on the base glass layer using tiny drops of white glue and your tweezers.  Mica is quite fragile, I find it easiest to use tweezers to move it around.

3. Create a path for air to escape.  We are going to use 4 different methods with the TOP layer of glass to allow gas to escape. These methods are:

  • The first is adding tiny frit pieces between the top and bottom glass layers (nipped from the original sheet of glass) to allow the bubbles to escape.
  • The second is to cut 1/2″ borders all the way around the top layer of the coaster.  I’m using the cut pieces to create a visual border design AND allow the bubbles to escape
  • The third is to cut the top sheet from corner to corner, again a design element AND a bubble escape
  • The fourth is to cut the corners of the top sheet diagonally.

This means our coasters will all be slightly different.  You can decide if that’s a great design choice for you or not, but it will demonstrate some different methods of achieving our end goals in terms of bubbles

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.

And the end results:

Conclusions and things to know:

  • The frit dots will require a longer hold than cut top layers of glass
  • The yellow color of the glass is caused by the Low E coating, you can read more about using Low E glass here
  • My coaster trick to get perfectly flat coasters is to put rubber feet on the top fused side and flip them over so the shelf side is now the top, ta da, perfectly flat.

Related Articles:

Fusing with Sheet Mica Tips and Tricks

Fusing with Metal Inclusions

Fusing with Dirt and Sand Inclusions