Cones are used in the firing process of making pottery. They measure the level of heat absorption to ensure proper firing and finished product. Kilns are not fired just to a certain temperature, but also to a specific cone level, or, heat absorption. Pyrometric cones are made from approximately 100 carefully controlled compositions and correspond (by number) to bend once a certain level of heat absorption is reached. The higher the cone’s number, the higher the level of heat absorption the cone is composed to measure. Starting at 10 (highest level), cones range down to 1 and then continue sequentially on: 01, 02, 03, etc. Each cone number is unique and measures within 30 degree temperature range.
Once my kiln is loaded and ready for firing, I place the cones throughout the kiln to ensure even heating. During firing I check the cones to see if they have started to bend. Cones look not unlike a gnome’s hat. Prior to heating they are bent to an 8 degree angle. As heat is absorbed, they begin to bend. Since the final temperature is most affected by the rate of temperature increase over the last 300 –400 degrees, it is imperative to keep a close watch on the cones. In a perfect firing, the cone will bend to a 90 degree angle.
Usually, I use “cone 5”. Below is an example of cones post firing.
Typically, I use sets of 3 cones. The triad of cones number in succession; if firing to cone 5, I would use a cone 4 and a cone 6 as well as the 5 to best measure the level of heat absorption. Once cone 4 begins to bend, I know I will need to begin shutting down the kiln.
Cones, cones, cones!
No comments:
Post a Comment