DIY Network

Glazes and Kilns Some tips on glazing and firing.... From "Throwing Clay" episode DTHC-108

Master potter Bill Van Gilder is making a set of dinner plates. So far, he's thrown three plates of graduated sizes. He left the base of each plate 1/2" thick, so he can later trim a foot on each plate. He stretched the rims between his fingers to give the plates their shape.

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After they dried stiff-leather hard (figure A), he inverted the plates on a clay pad and, starting with the largest plate, trimmed the underside to mirror the interior profile. He cut a foot ring in each plate and removed 1/4" from the base. When the plates were bone dry, they were loaded into the kiln for their first firing. The kiln fires for 10 to 12 hours, then cools for another 24 hours before Bill can remove the plates. The plates are now ready to be glazed (figure B).

Figure A

Figure B

1. Bill made test tiles from the stoneware clay and tested a variety of glaze colors. He chose nutmeg and cream-rust colors for the plates. When the two colors cross over each other during the glazing process, they produce a very subtle third color (figure C).

2. Before he glazes the plates, Bill paints wax-resist emulsion on the bottom rims of each. He also waxes a circular area in the center of each. This prevents the plates' low point from sticking to the kiln shelf during firing (figure D).

Figure C

Figure D

3. He inverts the plates on a cylinder to apply the wax (figure E). The wax is applied with two types of brushes, one with a pointed tip that will easily get into the corners inside the foot and a foam brush that is used to make the center circle on the plates. Bill is careful to use the same techniques while applying wax on each plate (figure F).

Figure E

Figure F

4. When the wax is dry, he dips the plates in the cream-rust glaze. The plates are dipped at an angle, creating an irregular line (figure G).

5. In between glazes, Bill removes any glaze drops caught on the wax, a step known as "fettling."

6. He prepares the nutmeg glaze. Because he is dipping multiple plates that will make up a set, he is careful to use the same hand movements each time he dips a plate in glaze (figure H).

7. After dipping the plates a second time, Bill again cleans any stray glaze drops off the wax emulsion.

8. After dipping the plates and letting the glaze dry, he loads them in the kiln for the high-temperature firing. The kiln will heat up to 2200 degrees over a period of 10 to 12 hours, before cooling for 24 hours, after which the plates can be unloaded.

Setting a table is easy when you have beautiful plates, and these plates even make clean-up easy, since they go from the table to the dishwasher (figure I).

Figure G

Figure H

Figure I

Temperature Cones, Rings and Kilns

Figure J

In addition to the computerized controls, some potters use temperature cones in electric kilns. Steve Lewicki, of L & L Kiln Manufacturers, uses this tried-and-true method of judging temperature with his kilns. The cones let the potter see exactly what's happening in the kiln. This very precise measurement is known as "heat work," which is the amount of heat that goes into the ceramic.

Cones come in different cone levels. Bisque, for example, is usually fired at cone 05 or cone 06, whereas most glazes are fired at cone 6. Cones start out perfectly straight; when perfectly cured, they are curved in the shape of a claw (figure J).

Denny McLaughlin, a veteran potter from Morton, Minnesota, relies on temperature cones for precise temperature readings in his wood kiln. Because the cones are made of the same material as the glazes and designed to melt consistently at the exact temperature each time they are used, he is always aware of how the glazed forms are progressing during the firing process (figure K).

Firing in a wood kiln can be tricky, taking both skill and vigilance to achieve the right results. To aid in judging the progress of the pots inside the kiln, Denny uses clay rings in addition to temperature cones. Rings, made from the same material and glaze as the pottery, are one of the simplest and oldest ways of judging what the glaze is doing in the kiln (figure L). Cones tell the potter the temperature in the kiln; rings show exactly what is happening to the glaze surface during a kiln firing. Potters use both methods of judging temperature and condition of the clay simply because the more information they have, the better their chances are of achieving the exact results they want during firing (figure M).

Figure K

Figure L

Figure M

RESOURCES :

Kilns
L & L Kilns
Website: www.hotkilns.com

Clay
Highwater Clays
Website: www.highwaterclays.com

Extruders
American Art Clay Co. Inc. (AMACO)
Website: www.amaco.com