Small Pyrometric Cone 4 for Kiln-Sitter

This is Cone 4 in Orton's small regular SRB series, made for the Dawson Kiln-Sitter rather than the kiln shelf. Orton lists it bending at 1209°C (2208°F) at 300°C an hour, the only rate published for this size, measured in a gas fired kiln. The cone is tapered, so where the sensing rod sits on it makes a difference. The thin end fires cooler and the thick end hotter, and the gap between them is about half a cone. Small cones also bend 7 to 10°C (12 to 18°F) earlier than a self supporting cone of the same number, so do not use a self supporting figure for one of these. Orton lists cones in this part of the range for porcelain, stoneware, china and floor tile. If a firing comes out short, Orton says to load the next cone hotter into the Kiln-Sitter and put a witness cone on the shelf to see what the kiln actually reached.