5
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 the upper 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 (see lower photo), 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 be-
tween a 3 o’clock and a 6 o’clock
bend is only a few degrees of
temperature.
HowtoCorrectforUnder-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 15.)
Compensating for an Under-Fired Cone
IFire to the same cone number next time, but add hold
time. How much hold time to add is a matter of experi-
mentation. Ageneralguidelinewouldbe 10-30 minutes.
IIf the kiln still does not fire hot enough, then fire to the
next hotter cone number, without hold time.
IAnother option: customize the firing in Ramp-Hold.
See the next page.
Compensating for an Over-Fired Cone
IFire to the next cooler cone number.
IIf firing to the next cooler cone number results in un-
der-firing, add hold time.
IAnother option: customize the firing in Ramp-Hold.
See the next page.
Cone-Fire Hold
Cone-Fire Hold heat-soaks the ware at the cone temper-
ature 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:
ITo even out the temperature throughout the kiln.
ITo 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.)
ITo help glaze absorb china paint.
ITo heal glaze defects such as bubbles.
CAUTION: Use Hold sparingly. A little hold time can
yield dramatic results. But too much hold time can eas-
ily 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
next cone will vary. As a rule of thumb, 45 - 60 minutes of
hold = one cone of heat work.
Example: to fire to cone 05, program Cone-Fire for 06
and add 45-60 minutes of hold time.
If your kiln has a peephole, watch the pyrometric witness
cones during firing. Press when the correct witness
cone bends. Note how much Hold time was needed. Pro-
gram that much Hold time the next time you fire the same
type of ware.
Note: During Hold, the display temperature will alter-
nate with time left in Hold. To figure hold time for the
next firing, subtract time left in Hold from the total
Hold time entered.
When Hold is set to 99.99 hours, the Sentry Xpress will
remain at that temperature indefinitely, until is
pressed.
When the Kiln Shuts Off
Too Soon
If the kiln shuts off before the pyrometric witness cone
bends, you can turn the hot kiln back on and keep firing.
From , program the next hotter cone in
Cone-Fire.
will appear. To begin firing, press .
will appear and the Run indicator light will
begin blinking. The hot kiln will begin firing, taking
up where it left off.
How to Customize Cone-Fire
You can customize a Cone-Fire program using
Ramp-Hold. (See the next section.) On pages 13 and 14, ta-
bles show the segments used to program each cone number
in Cone-Fire. For instance, a cone 016 firing at medium
speed ( )uses these two segments:
Rate Temp.
Segment °F/°C °F/°C Hold
1 396/220 1314/712 00.00
2 108/60 1422/772 00.00
An under-fired cone.
An over-fired cone.
