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Between 1000°F and 1250°F (538°C
– 677°C), the glass is softening, becoming
more pliable, and starting to act more like a liquid and less like a solid. At the top
end of this temperature range, glass will slump if held for a period of time.
Visually the top layer of the glass will begin to soften and round over on the
edges and the sides will start to become wet and glossy looking, or fire polished.
At this point, the layers of glass haven‟t begun to stick together yet.
Between 1250°F and 1350°F (577°C - 732°C), the glass is becoming even softer,
and at the top end of this range will be fully slumped. It‟s not recommended to
exceed 1350 F if you are slumping because at higher temperatures, there is a
loss of control of the glass and it may slide down too far or unevenly into the
mold. Visually the edges have softened and rounded even more and the surface
is very glossy. If your project is held for an extended period of time in this
temperature zone, it will be more prone to devitrify. Devitrification is the
compositional change of the glass from an amorphous material to a more
crystalline structure. As the molecules crystallize, devitrification appears to cloud
the surface of the glass.
Between 1350°F and 1400°F (732°C
– 760°C), the glass will have very round
edges on the surface and will stick together and become fully tack fused.
Between 1400°F and 1500°F (760°C
– 816°C) the glass becomes more fluid and
fully melts together at the higher end of this temperature range, which is a full
fuse.
Firing Process
In fusing, the fired appearance of the glass is referred to as the firing process for the
purpose of a selecting a firing schedule.
Full Fuse:
The glass has been completely melted together into
one solid piece of glass that is smooth on the
surface and all of the edges are well rounded.
Tack Fuse:
Glass has a textural feel on the surface. All the
edges of the surface pieces are well rounded and
fully attached to the base glass.
Slumping:
The glass has been placed onto a mold and bent to
shape and conform to the mold.
Fire polish:
All surfaces of the glass have been fired to a glossy
finish, yet the outside edges of the piece are crisp,
clean, and somewhat square.
