| Web Extras: Clay Selection, Temperature Cones |
| Using the right kind of clay for your projects is essential. |
From "Throwing Clay"
episode DTHC-108 |
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Using the right kind of clay for your projects is essential. Below, some helpful tips to use before you begin your next project.
- Clays are rated according to several factors: firing and maturing temperature, aggregate content (coarse or smooth), and color.
- Pick clays that mature and become nonporous at their glaze firing temperature.
- For functional kitchen use and tableware pottery, use clays that are of low to medium coarseness. Clays that are overly coarse will chip easily over time.
- Much like a painter's white canvas, clays that are light toned (gray or white) will lend brightness to a glaze.
- Dark-toned clays (tan, red, brown or black) can add depth and richness to a glaze color as the iron oxides contained in the clay blend chemically, upon heating, with the glaze coating.
- Clays shrink as they are dried and fired. Be aware of the shrinkage percentage rate for your particular clay, especially as you make containers of a specific capacity. For example, a mug made to hold 12 ounces of liquid will have to be made at the wet stage as a 14-ounce container, allowing for shrinkage to 12 ounces.
- Use clays that are the correct consistency for your project: softer clay for flat and small forms; stiffer clay for tall and large forms.
Reading and Interpreting Temperature Cones - Follow the manufacturer's instructions as to mounting cones into a clay support pad. Each cone will be set at an angle into the clay support pad, and the degree of angle is important.
- To observe temperature variations from the top to the bottom of your kiln, place a "cone pack"" (a series of cones) on a shelf behind each top and bottom spy hole.
- Place each cone pack an inch or two inward from the kiln shelf edge at each top and bottom spy hole. This placement position gives a true cone reading of the kiln's heat-saturated temperature.
- Keep a record, or "kiln log," of finished and cooled melted cone positions relative to successful and well-fired glaze surfaces. This will help to repeat a particular firing schedule to reproduce consistent glaze results.
- Use this chart to gauge glaze-firing temperatures relative to the cones placed in your kiln.
- For a chart of temperatures and cones, visit www.ortonceramic.com.
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
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