The coolest cone number is O22 and the hottest is 42. The first cones were numbered from 1 to 20. When cooler cones were developed, an 'O' was placed before the number. So cones cooler than Cone 1 increase from O1 to O2, etc. to O22. Cone Bending Both temperature and time and sometimes atmosphere affect the final bending position of a cone.
Temperature is the predominant variable.
We refer to the temperature as an equivalent temperature, since actual firing conditions may vary somewhat from those in which the cones were originally standardized. Using charts available from Orton, an equivalent temperature can be determined by measuring the final bending position of the Cone, if the heating rate is known. The cone bends when glass forms and it becomes soft. The composition of the cone and the amount of heat determine when and how much glass if formed. Changes in weight affect the bending of the cone.