Wednesday, 4 December 2019

Pot Melt Temperature Effects

When firing a pot melt, you have to consider how high a temperature you wish to use.

Viscosity is reduced with higher temperatures so increasing the flow and reducing the length of soak, although there are often some undesirable opacifying effects.

The size of the hole is also relevant to the temp chosen. The smaller the hole, the higher the temperature will have to be to empty the pot in the same amount of time. Of course, you can just soak for longer at a lower temperature to achieve the desired object of emptying of the pot without changing the temperature.

Using the same principle, the larger the hole the lower the temperature required to empty the pot in a given amount of time.

The temperature used to empty the pot will need to be between 840C and 925C. The problem with temperatures in the 900C to 925C range is that the hot colours tend to change, e.g., red opal tends to turn dark and sometimes become brown. Some transparent glasses also opacify. There is also the possibility that some of the glasses will change their compatibility.

So the best results seem to come from temperatures in the 840 to 850C range with longer soaks than would be required at 925C - possibly 4 or more hours.

Also remember to give melts a longer than usual anneal as they will be thicker than 6mm at the centre - somtimes as much as twice the edge thickness.

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