Pots

For this firing, we made a new, smaller rectangular pot which holds about 4kg of glass. This pot type did not fare well on the whole, and we lost seven or eight of them, appearing to be due to the too-sharp corners presenting a weak or stressed area. The small, square pots, though, did not break with as much rapidity.

In general, though, all of the pots, including the large rectangular pots, cannot withstand the thermal shock of cooling overnight and reheating the next morning, even though we empty out as much glass as possible each evening. A new arrangement needs to be worked out, and this is addressed in the furnace rebuild.

We also tried a new version of the daub nest, with the side wall only about 5cm tall. The aim was to protect the corners between the base and walls of the pot. This did appear to help, with a couple of the small rectangular pots lasting for several days. We also only fired the nests to about 1000°C, which enabled them to withstand thermal shock much better.

The photos include a sequence showing glass 'cakes' packed into a pot, its subsequent breaking by the force of the 'cakes' cracking due to heating, and the fire removed and put into a barrow whilst the pot was replaced and refilled. See 'Pot Filling' on the Furnace Performance and Lehr page.

Collars

We made several new collars, and fired them to 1000°C. We found that they did not shrink as much and lasted much better than those fired to 1100°C or so, and only had to replace two of them (we still had a supply of collars from the previous firing). They also fitted the gathering holes much better.

Interestingly, the two we had to replace both had a layer of ceramic cloth sandwiched inside them, which was meant to act as a reinforcement to the collars!