Glass 101; What Is A Firing Program; Heatwork; Size And Mass - Skutt Klin Operation Manual

The following guidelines just scratch the surface of the knowledge base associated with fi ring glass. We highly
suggest you take a fi ring class from your local dealer. If classes are not available in your area there are numerous books
available on the subject that can be found at bookstores and on the internet.

What is a Firing Program?

Glass is very sensitive to changes in temperature below 1000 °F. If it
is heated or cooled too quickly through certain temperature ranges it creates
stress within the glass which can cause breakage. Firing programs are used to
control these temperature rates and limit the amount of stress created within
the glass as well as create the desired effect on the glass.
A fi ring program is composed of one or more fi ring segments that dic-
tate the heating or cooling rate throughout the program. Each one of the lines
in the chart represents a segment or hold time within a segment and the slope
of the line represents the rate of fi ring. A fi ring program is either entered into
a kiln controller or on kilns without controllers it is replicated by turning up and down temperature switches .
Type of Glass
The art of fi ring glass has been around for centuries however, comparatively speaking, it has only been recently
that companies have begun manufacturing glass specifi cally designed to fuse together. Glass, like most everything on
earth, expands when exposed to heat and contracts when it is cooled. It expands at a measurable rate, known as the
COE, or coeffi cient of expansion, and as it becomes liquid it fl ows at different rates which is referred to as it's viscosity
level.
These variables and a host of others must be carefully managed to create glass that can be fused together without
crazing, cracking, warping, or breaking. Always consult with your supplier of glass to determine if the glass you wish to
fuse is compatible. All System 96 Glass is compatible.

Heatwork

Heatwork is a term used to describe the relationship of time and temperature and their combined effects on glass.
To a certain extent the two are inversely related. This means that the higher the temperature the less time is needed to
create the same effect and likewise, the lower the temperature the more time is needed.
This concept becomes most useful at the "Process" temperature range of glass. This is the temperature range
where the glass is fused, slumped or sagged. Most fusing glass will fuse between 1450 °F (788 °C) and 1480 °F (804
°C). It is possible to get the same results (or the same amount of heatwork), by bringing the kiln to 1450 °F (788 °C) and
holding it at that temperature for 30 minutes as you would by bringing the kiln to 1480 °F (804 °C) and holding it for
only 10 minutes. There may be other factors that make you choose one working temperature over the other such as the
thickness of the project.

Size and Mass

The size of the piece is one of the most infl uential factors for creating a fi ring program. One of the keys to suc-
cessful heatwork is having the entire piece go through critical temperature ranges at the same moment. When a piece
is thick it takes longer for the center to heat up then it does the outside of the piece. When it is a large diameter, slight
differences in temperature throughout the chamber of the kiln can cause the piece to expand at different rates.
The key to fi ring larger and thicker pieces is to slow the fi ring rates through critical temperature ranges. Determin-
ing how slow is often a trial and error proposition, therefore it is best to start with a conservatively slow program. More
projects are ruined by going too fast than too slow.
G 101
LASS
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