People frequently report success in
combining incompatible glass pieces with a larger, different base.
Questions arise.
Have the resulting pieces been tested for evidence of stress with
polarised light filters?
Other destructive methods such as hot
water, or placing in the freezer are not adequate measures of the long-term
effects of incompatibility stress. When
you are doing something outside the accepted norms, then you must test for
stress to be certain what you are producing remains sound before announcing
success.
Why does glass with incompatible pieces survive?
Incompatible glass will show some
stress when viewed through polarised filters. You will need to decide when it
is excessive. When viewed between polarised
light filters high stress will be shown by a rainbow effect in the halo of
light. Lesser stress will be shown by pale
light. The degree of stress will be shown by the amount of light.
Survivability
There are some circumstances where
the glass can contain the stress, and others where it cannot.
Generally, large mass pieces can contain the stress from small incompatible
pieces of glass.
Spherical
objects can contain a lot of stress over a
long period, which is why glass blowers and lamp workers are generally less concerned about
incompatibility than kilnformers are.
Flat glass pieces behave a little
differently.
Circular
forms can contain stress more easily than
other shapes. Rectangular shapes generally
show the most stress at the corners. Narrow or wedge-shaped pieces have the
most difficulty in containing stress. The stress is concentrated at the points.
The placing of the incompatible glass is also important to the
survivability of the glass. The further
from the edge of the piece, the less likely there will be breaks.
The smaller the pieces of incompatible glass in relation to the whole,
the less risk of breaking.
The more spread apart the pieces are, the greater the chances of survival
for a while or long term.
The most essential piece of equipment for people starting out and those who are investigating new setups or working at the edges of accepted norms is a pair of light polarising filters to test for stress.
When combining incompatible glasses the
general case is that the greater the mass of the whole object in relation to
the incompatible glass, the greater the chance of survival.
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