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The best way to use this tutorial is to start at the beginning and
move through at your leisure, stopping and re-starting when you wish to. When you've completed the various
sections, you'll have a solid background in fusing and slumping and a basic
understanding of topics such as glass compatibility and the concept of
annealing. Jump around if you must, but the sections build on each other
so it's a good idea to at least briefly hit them all.
If you are already familiar with kiln-forming basics, you can use the links
below to jump directly to the section you wish to review.
What is warm glass? What is kiln-forming?
The term warm glass refers to fusing, slumping, and other glass
processes which take place at temperatures between 1100 and 1700 degrees
Fahrenheit (600 to 925 Celcius). That doesn't sound warm, but it is when you compare it a
glassblower's working temperatures, which often exceed 2000 degrees
Fahrenheit.
Another term for these processes is kiln-forming.
It's not unusual for the two terms -- "warm glass" and "kiln-forming" -- to be
used interchangeably, although in recent years "kiln-forming" has become the
preferred term, while "warm glass" has increasingly been used to refer to this
website.
What are fusing and slumping?
Glass fusing is the process of using a kiln to join together
pieces of glass. If you apply heat to glass, it will soften. If you
continue to apply heat, the glass will become more fluid and flow
together. Two or more pieces of glass will stick (or "fuse") to
each other. When the right kind of glass is heated and then cooled
properly, the resulting fused glass piece will be solid and unbroken.
Many people also use the word "fusing" to include bending and
shaping glass using the heat of a kiln. This manipulation can take many forms,
but the most common is slumping, where a mold is used to cause
already fused glass to take on the shape of a bowl, a plate, or similar object.
Other kinds of manipulation done with fusing techniques are combing,
which involves using a tool to distort the shape of the glass while it is hot,
and fire polishing, which uses a kiln to heat the glass just enough
to make it shiny and smooth.
Another category of kiln-forming activity involves the use of molds to form glass into
more complex shapes.
Virtually any shape that can be formed in clay or wax can also be made in
glass. These more advanced kiln forming processes include kiln casting (melting glass into a mold inside a kiln,
pate de verre
(forming shapes by heating a "paste of glass" inside the kiln), and
glass casting (pouring molten glass into a mold). These processes
tend to be more complicated than basic fusing and slumping.
The table below summarizes the major kiln-forming techniques.
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