Manual Glass Kiln

Segment 1 heats the wax to 300°F/148°C and holds it for
one hour, allowing it to drip from the mold.
Segment 2 hardens the mold.
Segment 3 lowers temperature to 800°F/426°C, the typi
-
calcastingtemperatureforsilver.(Mosttypesofgoldcastat
900°F/482°C.)
Note: Casting temperature depends on the size of
themold.Thetemperaturesaboveareonlyaguide.
See your jewelry supply dealer for temperature
recommendations.
Burnout Instructions
1 Place a metal tray inside the kiln on three ½” posts.
Place the mold on a wire mesh screen on top of the
tray.Themold’ssprueholeshouldbedown.Thetray
willcatchmeltingwaxasitdripsfromthespruehole.
2 Keep the kiln’s vent hole(s), if any, open during wax
elimination. If the kiln has no vent hole, leave the
door open½”. Thisallows fumesto escape from the
kiln. Heat the kiln to 300°F/148°C and hold it at that
temperature for at least one hour.
Note: Do NOT heat the wax above 300°F/148°C.
Hold at 300°F/148°C for at least one hour. During
this hour,the waxwill meltfrom themold anddrip
into the tray. If the kiln gets hotter than
300°F/148°C, the wax may smoke and deposit car-
bon inside your kiln, causing expensive damage.
3 Afteronehourat300°F/148°C,openthekiln.Remove
themoldandwaxtray.Pourthewaxfromthetrayand
leavethetrayoutofthekilnuntilyournextwaxelimi-
nation. (Do not leave the tray in the kiln!)
4 Heat the mold to the temperature recommended by
yourjewelers’supplyhousewhereyoupurchasedthe
moldmaterial.Thisisusuallyaround1350°F/732°C.
5 Lowerthetemperaturetothecastingtemperatureof
the metal. Hold at that temperature until you are
ready to begin casting. Removethe mold withtongs.
Wear protective gloves and safety glasses.
Saving a Carbon-Damaged Kiln
Ifyoufollowtheabovedirections,yourkilnshouldbesafe
from wax damage. In some cases, a small amount of carbon
mayformonthewallsoveraperiodoftime.Thisisduetothe
burningofwaxresiduethatwasleftinthemold.Forthisrea
-
son we recommend that you periodically fire the kiln to
1500°F/815°C as follows:
1 Open the vent cover(s) or leave the door ajar ½”.
2 Fire the kiln empty to 1500°F/815°C at a rate of
300°F/166°C with a one hour hold (01.00).
Firing Mistakes
Silver Clay
Cracks
Cracks that appear in fired silver clay may be due to too
much water in the silver clay before it was fired. Another
cause is careless handling of a dried, unfired piece. To re
-
pair, fill the crack with silver clay and fire again.
Brittle
Silver clay will not reach full strength if underfired. You
may be able to save the piece by firing again to the correct
temperature and hold.
Too Much Shrinkage
When silver clay is overfired, it shrinks too much and
loses detail. If the kiln is firing hotter than the temperature
programmed, check the position of the thermocouple (see
page17,bottomleftcolumn).Replacethethermocoupleifit
is old.
Glass
Glass Cracking
Probable Causes:
I
Heating the Kiln Too Fast
I
Cooling the Kiln Too Fast
I
Fusing Incompatible Glass
I
Not Enough Glass Separator on Shelf
Mostproblemsinfusingarecausedbyrushingthefiring.
Theglass mustchange temperatureslowlyduring thecriti
-
cal temperature range of 100° - 500° F / 37° - 260°C. This
critical range applies to both heating and cooling.
The second critical temperature range is annealing,
whichisthecoolingrangeof950°-700°F/510°-371°Caver
-
age. Cool the glass slowly during this range so the stress in
the glass will have time to dissipate.
If you become im
-
patient after the glass
has fused and you
crack open the door of
the kiln for a few sec
-
onds to peek inside,
you may hear a “ping,”
which is the sound of
glass cracking. Avoid
the temptationto open
thedoor.Waituntilthe
kilnhascooledtoroom
temperature. Some
artists schedule their
fusingsothatitiscom
-
pletedbeforetheygoto
bed. That waythey will
15
Flaking glass separator can cause the
glass to crack. This is because the glass
sticks to the shelf.