Use Orton Pyrometric Self-Supporting Witness Cones to make sure your kiln is firing to Cone O6. Cones feature a built-in base with correct height (1 3/4") and angle (8 degrees) to help ensure reproducible firings. We recommend using cones at least once per month for maintenance. Place 1 cone on your top, middle, and bottom shelf to ensure all areas of your kiln are reaching Cone 06. A perfect arc that just touches the kiln shelf indicates the kiln fired to Cone O6. An arc that slumps onto the shelf means the kiln fired above Cone 06. An arc that doesn't touch the shelf indicates that the kiln fired cooler that Cone 06. Each box includes 25 cones.