Skutt FireBox8x6 LT - Manual (Page 8)

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8
Overview
Cone Fire Mode was developed by Ceramic Engineers to provide artists with an easier way to
fire their kiln. In the past artists had to use Pyrometric Cones. Pyrometric Cones are pyramid
shaped clay formulations which were designed to bend when they received the appropriate
amount of heatwork for the clay or glaze inside the kiln. The artist would look into the kiln
through peep holes and when the cone softened and bent, they would shut off the kiln. This is
why every clay and glaze has a cone value associated with it.
Cones used in electric kilns range from 022 to 10. It is helpful to think of the “0” as a minus
sign. The higher the number, the higher the temperature. For example a Cone 04 is hotter
than a Cone 06 and a Cone 6 is much hotter than a cone 06.
Thanks to modern electronics we can now simulate the heatwork measured by cones with
Electronic Kiln Controllers. Cones are used primarily for testing and troubleshooting your kiln today. An added
bonus of controllers is that we can more accurately control the firing speeds before and after the kiln reaches
peak temperature to produce special glaze effects and protect fragile pieces through critical firing ranges.
Preheat
The first question the controller asks you when you are using ConeFire
Mode is “How Long Do You Want To Pre-Heat?”. Preheat was intro-
duced to help prevent ceramic pieces in the kiln from cracking due to
rapidly escaping moisture in the piece. Water turns to steam at 212 °F
(100 °C). If you fire fast, the steam wants to escape, and when it does,
it can crack or shatter your ware.
An easy way to tell if a piece is still wet is to hold it up to your cheek.
If it feels cool it still has moisture in it. Under normal conditions smaller
pieces (like the ones that would fit in your kiln) take about a week to
dry.
If you are not sure if your ware is completely dry, adding a preheat time
is good insurance. Usually 1 to 2 hours is sufficient. When a Preheat
time is entered the kiln rises in temperature at a much slower rate than
normal until it reaches 180°F (82 °C) and then holds at that tempera-
ture for the amount of time you entered. During this Hold time you will
see the kiln counting down the time alternately with the current tempera-
ture of the kiln.
Remember that when you are entering time in your controller that the
numbers to the left of the decimal equal hours and the numbers to the right of the decimal equal minutes.
Entering Cone Value
Every commercial clay and glaze should have a cone value of
or range of cones printed on the label. It is very important not to
exceed this rating. Raw materials used in clay and glazes can vary
drastically on their melting point. Earthen Ware clays generally fire
in the 04 - 06 range. Porcelain and Stoneware generally fire in the
6 - 10 range. If you fired earthen ware to Stoneware temperatures it
would most likely melt all over the shelf. If you are ever unsure of the cone value of a particular clay or glaze
ask your clay supplier. They should also have good knowledge of the preferred Cone Values to use when firing
greenware (Bisque Firing) or when firing glazed bisque (Glaze Firing).
2000
1800
1600
1400
1200
1000
800
600
400
200
0
0 2 4 6 8 10 12
Temperature (∞F)
Hours
250∞
1000∞
1150∞
1694∞
1946∞
Cone 04, Medium Speed
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