Firing Schedules; How To Interpret The Bending Of A Pyrometric Cone; How To Correct For Under- Or Over-Fired Cones - Sentry Xpress 5.0 Instructions For Use Manual

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If you use the three cone system, always have the
higher temperature cone on the same side in every
firing. Otherwise you can lose track of which cone is
which.
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Wear green #3 kiln firing safety glasses when view-
ing the cones through the peephole.
See your dealer if in doubt about which cone number to
use with each clay and glaze.

Firing Schedules

Cone-Fire uses three ranges of firing schedules:
Low fire cones 022 - 011
Medium fire cones 010 - 01
High fire cones 1 - 10
The firing schedules programmed into Cone-Fire mode
are listed on pages 30-31. Should you ever want to custom-
ize a Cone-Fire program, make the desired changes to a fir-
ing schedule and program it in Ramp-Hold (page 11).
CAUTION: Cone numbers beginning with 0 are
lower in temperature than those without the 0.
When programing a Cone-Fire, be sure you know
the difference between an 05 and 5. See "Tempera-
ture Equivalents Chart for Orton Self-Supporting
Pyrometric Cones," page 32.
Low Fire Cones 022 - 011
This range includes decals, over-decorations, lusters,
and golds. You can usually fire fast. Good venting is impor-
tant because of the oils and other organics. Do not close the
lid from the vented position until all odor has disappeared.
Middle Fire Cones 010 - 01
Glazes fired on bisque ware (ware that has already been
fired) can be fired faster than greenware.
High Fire Cones 1 -10
This is the firing range for porcelain and stoneware.
These bodies fire nearly to vitrification and can shrink up to
16%. Water, carbon and sulfur burn out during the early
stages and must be vented. The amount of oxygen in the
kiln affects the color of the fired clay. The high fire sched-
ules programmed into Cone-Fire slow down during the last
216°F/120°C (two hours) to produce better density in the
ware.
How to Interpret the Bending of a
Pyrometric Cone
The cones illustrated here are called self-supporting
cones. They are the easiest type of witness cone to use.
Keep the kiln lid or door closed when the kiln is not in use.
1. Correct Bend
When the self-supporting cone
bends so that the tip is approxi-
mately even with the top of the
base, the cone has been exposed to
the correct amount of heat work
for that cone number. This is
called a 6 o'clock bend.
2. Under-Fired Cone
The cone in this photo 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 pud-
dles, 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 instance, 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 32.) Try the following ideas, one at a time:
Compensating for an Under-Fired Cone
Fire to the same cone number next time, but add hold
time. How much to add is a matter of experimentation.
A general guideline would be 10-30 minutes.
If the kiln still does not fire hot enough, then fire to the
next hotter cone number, without hold time.
Adjust the Thermocouple Offset. See page 20.
Customize the firing in Ramp-Hold. See page 11.
Compensating for an Over-Fired Cone
Fire to the next cooler cone number.
If firing to the next cooler cone number results in un-
der-firing, add hold time.
Adjust the Thermocouple Offset. See page 20.
Customize the firing in Ramp-Hold. See page 11.
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