Instruction manual

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Cone-Fire
Cone-Fire mode is based on pyrometric
cones. It is not designed for heat treating,
glass fusing and enameling. For these
firings, use Ramp-Hold mode (page 6).
Use Ramp-Hold to fire ceramic pieces
that require a custom firing schedule.
You can also use Ramp-Hold to add a
slow cooling.
Pyrometric Witness Cones
It is important to understand pyrometric witness cones,
because clay and glazes are rated to cone numbers. Pyromet
-
ric cones are small pyramids of clay that bend when exposed
to the correct amount of heat work. Cones are rated by num
-
ber. See page 14 for a list of cone numbers and their temper
-
atures.
When a witness cone bends during firing, the clay and
glaze in that firing, rated to that cone number, have received
the correct amount of heat.
Place the pyrometric witness cone on the kiln shelf near
the ware you are firing. Use the cone to check for firing accu-
racy. The cone is the most accurate measurement of heat
work in a ceramic firing. This is because the cone measures
the combined effects of time, kiln atmosphere, and tempera-
ture.
We suggest using the witness cone to trouble shoot prob-
lems with the ware. If china paints appear faded and you sus-
pect it is due to over-firing, test fire with a witness cone. An-
other example: glaze crazing due to under-fired bisque.
How to Interpret Cone Bending
The cones illustrated here are called self-supporting
cones. They are the easiest type of witness cone to use.
1. Correct Bend
When the self-supporting
cone bends so that the tip is ap
-
proximately even with the top of
the base, the cone has been ex
-
posed to the correct amount of
heat work for that cone number.
This is called a 6 o’clock bend.
2. Under-Fired Cone
This cone has not bent far
enough. It indicates that the kiln
did not fire long enough or hot
enough.
3. Over-Fired Cone
When a cone collapses, or
puddles, it indicates that the
kiln over-fired the ware rated to
that cone number.
Note: Do not be overly con
-
cerned with achieving an
exact 6 o’clock bend. The
difference between a 3 o’clock and a 6 o’clock bend
is only a few degrees of temperature.
How to Correct for Under or
Over-Fired Cones
Before changing a firing because of an under or over-fired
cone, make sure the correct cone was in the kiln. For in
-
stance, if you fired to cone 05, make sure the cone in the kiln
was not a cone 5 instead. (See the cone temperature chart on
page 14.)
Compensating for an Under-Fired Cone
I
Fire to the same cone number next time, but add hold
time. How much hold time to add is a matter of experi
-
mentation. A general guideline would be 10-30 minutes.
I
If the kiln still does not fire hot enough, then fire to the
next hotter cone number, without hold time.
I
Another option: customize the firing in Ramp-Hold. See
the next page.
Compensating for an Over-Fired Cone
I
Fire to the next cooler cone number.
I
If firing to the next cooler cone number results in un-
der-firing, add hold time.
I
Another option: customize the firing in Ramp-Hold. See
the next page.
Cone-Fire Hold
Cone-Fire Hold heat-soaks the ware at the cone tempera
-
ture at the end of the firing. Without Hold, the kiln shuts off
after it reaches the cone temperature. Hold maintains the
cone temperature for the period you specify.
Hold is not needed in every firing. Experience will help
you decide when to use Hold. Some of the reasons you might
consider using it:
I
To even out the temperature throughout the kiln.
I
To allow heat to penetrate more completely into the clay.
(Rapid firing is like cooking: the turkey will be done on
the outside but not on the inside.)
I
To help glaze absorb china paint.
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To heal glaze defects such as bubbles.
Caution: Use Hold sparingly. A little hold time can
yield dramatic results. But too much hold time can
easily overfire your ware and burn out colors.
One way to add Hold time without over-firing is to fire to
one cone cooler than needed. Then add enough hold time to
bend the next hotter cone. Hold time needed to bend the