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Minnesota Clay Co. USA Technical Info - Pyrometric Cones
Cones are Cones. Or are they? Here are the differences.
 
Senior (Standard) Cones are normally set in a series of three ascending cone values in a clay plaque. The "Target" cone is the second cone in the series. Cone plaques are set opposite a "peep hole" opening in the kiln's interior. The kiln operator monitors the progress of the firing by looking through the peep hole and shutting off the kiln when the target cone bends to a "six o'clock" position.
 
Junior Cones are typically used in Dawson Kiln Sitter shut-off devices. The target cone is placed on the kiln sitter cone supports and under the sensing rod. When the Target cone begins to bend, the sensing rod lowers releasing the trigger weight on the outside of the control box. When the trigger weight falls, it shuts off the kiln.

Junior cones can be used in cone plaques in a similar fashion to the senior cones shown above. Junior cones used in this way are more difficult to spy and fire hotter than senior cones of the same cone value.
 
Pyrobars serve the exact same function as Junior cones in the Kiln Sitter, except Pyrobars aren't tapered and provide a more reproducible firing. As of 2018 we no longer stock or sell the pyrobar cones from Orton.
 
Popular Cone Values for Most Clays:
For Bisquing Earthenware Cone 06-04
For Glazing Earthenware Cone 05
For Bisquing Stoneware and Porcelain Cone 06-04
For Glazing Stoneware and Porcelain Cone 6 (can range from Cone 4-10)
See Clay Body Description For Specific Cone Range.