Air bubbles can appear in just about any fused glass project.
They are cause by air trapped in the glass.
Sometimes these are unwanted bubbles, but you can also set up your glass to achieve bubbles in your work.
Air bubbles can also be inside the glass when purchased.
By paying attention to how the air can get trapped between layers, you can minimize the amount of bubbles.
How to Avoid Air Bubbles
If your pieces are heated too quickly, the outside edges of your glass can soften and fuse before the inside glass does.
This will result in trapped bubbles.
You can reduce these bubble formations by adding a pre-rapid heat soak to the firing cycle.
Try holding the kiln at a temperature between 1150 to 1250 degrees Fahrenheit for about 15 to 45 minutes.
This should allow all of the glass to soften, allowing the top layer to rest smoothly onto the bottom layer.
Pay close attention to where your pieces are on the kiln shelf.
If they are too close to the heating elements, the direct heat can cause the edges to seal up and thus cause bubbles.
Another thing that can cause bubbles is the texture of the glass that is being fused.
Sometimes air will become trapped inside the waves or texture of a piece.
Stacking can also cause bubbles.
Watch how you stack your pieces; be aware of any places where air might be trapped.
If smaller pieces are sandwiched between larger pieces, place some frit around the inside edge of this sandwiched piece and you could avoid bubbles.
Anytime you add frits, powders, or stringers between layers of glass there is an almost certainty that you will get bubbles.
If you want to place these objects between two pieces of glass, the best way to avoid bubbles is to fire the bottom piece of your glass with the frit, powder, or stringer layer to a full fuse.
Once you have done that, add the top layer and fuse the piece again.
If your kiln shelf is not flat, you can also get bubbles.
Check the shelf periodically to make sure it is flat and level.
Large Golf Ball Size Holes
An additional variety of bubble happens when air gets trapped between the firing piece and the kiln shelf.
These are due to a high temperature chemical steam that is given off by the ingredients in kiln wash.
These pockets come about usually when one large layer of glass is fired up to fuse temperature quickly.
These bubbles are usually quite large.
They grow and start to look like domes.
If these are heated long enough, they will pop.
This leaves a large hole in the glass.
There are a few things you can do to prevent these from occurring in your pieces.
1. Don't fire just a single sheet of glass on the kiln shelf. Use a minimum of two solid layers of glass in the design. The added weight of this second layer will help push the air bubbles out the sides of the piece.
2. When the glass has gotten to the softening point, slow down the rate of heating or do a soak. This slowing down or soaking will help the center of the piece heat up and allow the air to escape before the edges of the glass are sealed to the shelf.
3. Instead of just using kiln wash, try using fiber paper under the glass. This porous paper will allow air to escape during the firing process.
You can design bubbles in your piece of fused glass.
This can add design and interesting effects in your piece.
There are many ways this can be accomplished and even ways you can control where the bubbles will occur.
Bubbles don't have to necessarily be a bad thing.
They can be extremely dramatic and tantalizing.
Learn more about how to add bubbles to your fused glass and even how to control their placement on the
"Do You Want Bubbles"
Return to any of the following pages:
Air Bubbles to Glass Fusing Made Easy
Problems and Solutions
Glass Fusing Problems