Most people have difficulty seeing the witness cones on the kiln shelf during firing. But if you position them just right, you can see them even at cone 10, when the kiln interior turns white-hot.
Being able to see the cones during firing is your assurance that the kiln is firing normally. If the kiln takes longer than usual to fire and you cannot see the cones, you may worry that something has gone wrong. Maybe the kiln is even over-firing.
In formulating these guidelines, I tested a welder’s facemask, mirror, and high intensity flashlight. You don’t need those items, even for cone 10 viewing.
1) Place the cones 8” - 12” away from a peephole. Positioning them closer makes them difficult to see.
2) Have enough space around the cones to keep them from touching a piece of ware when they bend.
3) Position cones so that when viewed from the peephole, they are silhouetted by an element on the opposite kiln wall. (Keep cones at least 2” from an element.) 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) Wear firing safety glasses when viewing the cones through the peephole.
See your dealer if in doubt about which cone number to use with each clay and glaze.