Thursday, 20 January 2011

Heat Work

“Heat work” is a term applied to help understand how the glass reacts to various applications of heat. In its simple form it is the amount of heat the glass has absorbed during the kiln forming heat up process.

Heat can be put into the glass quickly, but to achieve the desired result, it will need a relatively higher temperature. If you put the heat into the glass more slowly, it will require a relatively lower temperature.

For example, you may be able to achieve your desired result at 814C with a 400C/hr rise and 10min soak. But you may also be able to achieve the same result by using 790C with a 250C/hr rise and 10min soak. The same amount of heat has gone into the glass, as evidenced by the same result, but with different kinds of schedules. This can be important with thick glass, or with slumps where you want the minimum of mould marks. Of course, you can also achieve the same results with the fast rise with a longer soak at the lower temperature, e.g. a 400C/hr to 790C with a 30 min soak.

The adage “slow and low” comes from this concept of heat work. The best results come from lower temperature processing, rather than fast processing of the kiln forming.