KNOWLEDGEBASE

How do hold times and heatwork affect my work?

  1. There is an option to add time to the end of the program that appears when you enter a program. Usually, there is no need for more than a few minutes of holding at the end. A hold allows the ware in the center of the kiln to achieve the same "heatwork" as the ware on the edges of the shelves. Heatwork is achieved by a combination of time and temperature (more time and/or more temp equal more heatwork... (heatwork can be thought of as the 'energy' that is given to the ware by the kiln, which ultimately bends the cone and melts the glaze). You can have too much heatwork- i.e. overfire the clay- if you have too much hold at the end, or go to too high a temperature. You can also overfire by climbing too slowly at the end of the firing. If you add more TIME by climbing slower or adding a hold, you must reduce the TEMP you are firing to... If you add more TEMP (by going to a hotter temp), you must reduce the amount of TIME by climbing up to temp faster.
  2. The nice thing is that the Easy-Fire programs (the slow bisque, slow glaze etc.) are programmed to automatically adjust the final temp when the rate of climb is faster or slower than what is prescribed. For example, the slow glaze program is set to climb at 120 degrees per hour in the last 250 degrees of the firing. If the firing is to cone 6 the kiln will shut off around 2237F. If the kiln is really fully loaded this time, it may start to climb slower than 120F per hour. If this happens, the controller automatically re-calculates a lower temp to shut off the kiln. If it did not do this the clay would overfire due to the slower rate of climb still going to 2238F
  3. Vary-Fire programs do not fire to cone numbers unless you set them to. When you program it to climb at 108 degrees F per hour to 2232F and it can only climb at 60F per hour, you will overfire the clay considerably if it still climbs all the way to 2232F.
  4. Your max hold at the end of any program should be no more than 10 minutes, unless you change the cone offset for Easy-Fire or the final temp for Vary-Fire to account for the longer hold. Even 10 minutes is about a half a cone hotter.
  5. Hold times and a lot of time at high temps are not kind on the heating elements. Kilns that are held for 20 minutes at temp typically get about half the number of firings as kilns that are not held at temp.