answers
courtesy Wikipedia.com
Fused
glass is
glass that has been fired (heat-processed) in a kiln at a range of
high temperatures from 593º C (1100ºF) to 816º C (1500ºF).
There are three main distinctions for temperature application and
the resulting effect
on the glass.
Firing
in the lower ranges of these temperatures 593º-677ºC
(1100º 1250º F) is called slumping. Firing in the middle
ranges of these temperatures 677ºC- 732ºC (1250º-1350ºF)
is considered "tack fusing". Firing the glass at the higher
spectrum 732ºC -816ºC (1350º-1500ºF) is a "full
fuse".
All
of these techniques can be applied to one glass work in separate
firings to add depth, relief and shape.
Most
contemporary fusing methods involve stacking, or layering
thin sheets of glass, often using different colors to create patterns
or images. The stack is then placed inside the kiln and then heated
through a series of ramps (rapid heating cycles) and soaks (holding
the temperature at a specific point) until the separate pieces begin
to bond together. The longer the kiln is held at the maximum temperature
the more thoroughly the stack will fuse, eventually softening and
rounding the edges of the original shape.
Once
the desired effect has been achieved at the maximum desired
temperature, the kiln temperature will be brought down to avoid devitrification.
It is then allowed to cool slowly over a specified time,
soaking at specified temperature ranges which are essential to the
annealing process. This prevents uneven cooling and breakage and
produces a strong finished product.