Dealing with Trapped Air Bubbles
This is part three of a
multi-part tip on ways to repair or eliminate trapped air bubbles.
Click here to go to part one.
An alternative method to eliminate or greatly reduce air bubbles
involves re-firing the piece to a temperature that's high enough to
allow trapped air bubbles to rise to the top of the piece and
escape. This approach can be used for both initial firings and
for re-firing pieces with trapped air bubbles.
To use this method, first fire your piece to around 1700F/925C.
At this temperature the viscosity of the glass will be low enough
that bubbles will rise to the surface of the glass and escape.
You'll need to soak the piece for a while to give the bubbles time
to pop, so watch carefully until the bubbles rise and pop.
Continue soaking until the glass smoothes out, then anneal and cool
Although this approach won't get rid of all of the trapped air,
it will tend to leave only very small bubbles or slight "pin pricks"
where the bubbles rose to the surface and popped. Be aware
that some glasses change color when fired to high temperatures.
There is also a tendency for devitrification; in addition, glasses
that are repeatedly fired to high temperatures can become
But the risks of firing to high temperatures are often outweighed
by the results. Firing to high temperatures almost never fails
to surprise, and usually yields results that can't be duplicated
with any other approach.
This technique, also known as high temperature
firing, will be discussed in more detail in a later tip.
Copyright 2006 Brad Walker.
All rights reserved.