The original Pyrometric Cones. Widely used as a witness cone on the kiln shelf to visually monitor the progress of the firing and "heatwork", a combination of time and temperature, throughout the kiln.
Large Cones need to be supported by cone plaque, a clay pat or a wire cone holder. Cones are mounted at an 8° angle and so either 1 ¾ or 2” of the cone is exposed above the pat.
Uniform mounting height and angle are very important.
Firing with witness cones is highly recommended. These are the Large (standard) cones that you put on the kiln shelves when firing a kiln. They will indicate the temperature ("heat-work") that location on that shelf has reached, thus they "witness" the true temperature achieved. In a typical firing, the kiln's temperature easily varies over one cone from top to bottom in heat, so you should put one Cone pat per shelf, in the center of the shelf, to get a good idea how you kiln is firing. A Cone pat is putting one cone on each side of your actual firing Cone that is one above and below your target. For example, for a Cone 5 firing, also put a Cone 4 and a Cone 6 next to your Cone 5 on the shelf. For Cone 05, also put an 04 and a 06 on the shelf. The lowest temperature Cone should be very bent, the middle somewhat bent (about 90 degrees), and the highest not bent at all.
If you have a kiln sitter, you also need Small cones to place in the kiln sitter. Cones placed in a kiln sitter are closer to the wall (and the heating elements), so they get hotter and would bend sooner than witness cones places on the kiln shelves. Accordingly, Orton adjusts them slightly to compensate for this. So, for a Cone 05 firing, you would put an 05 Small Cone in the kiln sitter.
Note that many people find that they have to put Cones in the kiln sitter that are 1 Cone hotter than desired to get the correct result on the shelf witness cones. For example, to achieve a witness Cone 06, you might need a Cone 05 (hotter) in the sitter. Or to achieve a witness Cone 5, you might need to use a Cone 6 in the sitter.
