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 3 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 of
this range 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.