Nearly every day on this forum someone, often me, refers to cones and their importance in the ceramic firing process. I understand how cones work. I explain it to my students all the time. But this week I found myself with a question about cones I've never encountered before.
When it comes to soaking (holding temperature) in order to achieve heat work, we always tell people to test it with actual cones. I've heard anywhere from 15 minutes to 1 hour of soaking is necessary in order to gain one cone. There's no consistency to the system.
Here's my recent experience that has me somewhat baffled: I used to fire to cone 8 in oxidation (electric). In order to increase the life of my elements a bit, I would fire to cone 6 with a 40 minute hold to reach cone 8. Now I fire to cone 6, and I finally tested the hold time to see how long it would take me to get from cone 4 to cone 6, and it came out to 75 minutes, almost twice as long as from cone 6 to cone 8!
The at a rate of climb of 108F/hr, which is what my firings use, the difference between cone 6 and cone 8 is only 48 degrees. The difference between cone 4 and cone 6 is 108 degrees. So can we assume that the greater the temperature gap, the longer the soak time in order to achieve the heat work? Those of you who soak for cones, what cones are you using, and how long is your soak time?