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How to Position Witness Cones on the Kiln Shelf

Pyrometric cones are small pyramids of clay that bend when exposed to the correct amount of heat work inside a kiln. Glass artists don't need cones, but we recommend them for ceramics, even in digital kilns.


In finding ways to view witness cones, I have experimented with a welder's mask, high intensity light, and mirror, items suggested by ceramists for this purpose. I have tried placing the cones close to the peephole, then on the opposite side of the kiln shelf away from the peephole. I have positioned cones both in front of an element, and in front of a piece of ware.

After all that testing, this is the method I found most effective for viewing cones:

1. Ironically, positioning the cones close to the peephole makes them difficult to see. They should be no closer than 8", no farther than about 12".

2. Position the cones so that when viewed from the peephole, they are silhouetted by an element on the opposite kiln wall.

3. The element that silhouettes the cones should be level with the lower part of the cone. If the element is in line with the upper part of the cone, you won't be able to see the cone when it bends.

4. 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.

5. Use firing safety glasses, available from Paragon for only $15.00.

6. Keep the cones far enough from the ware so that when the cones bend, they will not touch the ware.

If you follow these suggestions, you should be able to see cones even at cone 10.

With best wishes,

Arnold Howard Paragon Industries, L.P. - Better Designed Kilns 2011 South Town East Blvd. Mesquite, TX 75149-1122 Voice: 972-288-7557 & 800-876-4328 / Fax: 972-222-0646 /

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