Glass Furnace
An exciting weekend building a wood fired glass furnace from scratch.
By building a glass furnace a few of us decided to see if we could make our very own ‘Bristol glass’ as a way of paying homage to the tradition of my home town, Bristol, UK, which has a long history of glass making, dating back to the early 1700s. We thought we would dig up and melt sand dug up from around Redcliffe caves – the very sand that would’ve been used all those centuries ago for making glass.
Armed with only a down-loaded diagram of a glass furnace, a pile of sand and kiln bricks and enough wood to burn the Houses of Parliament, we started building a kiln.
Now I know how to use a kiln, but nothing about how to build a kiln. I quickly learnt that the most important thing to get right is the flow of air around the chamber. We agonised over the design, and must’ve had a hundred discussions on how to make a kiln before the glass furnace actually began to take shape.
Of course there was no way of knowing whether what we were building was going to draw sufficiently and whether we would be able to reach the temperature required – 1300 degrees C - to melt sand.
Our knowledge of how glass is made didn’t really help in this situation. To go with the sand in the crucible, we added very unscientific amounts of soda ash and limestone. That, coupled with the fact that the sand was full of impurities, meant that we would never produce something that resembled ‘real’ Bristol glass. Or even glass!
The whole weekend was a complete buzz. By the time we started feeding the furnace with wood, we were all fired up as much as the seven foot flames that shot from the top. So much for kiln safety! The kiln pyrometer and the spontaneous cheer told us we’d reached temperature – considering there was no kiln insulation it was surprisingly easy - and the ingredients were mixed with anticipation…
A skilled glassblower was on hand, but to no avail – our lumpy melted blob of sand was more like an over-cooked rock cake than glass, and was impossible to shape.
What a weekend, though. The energy we created together gave me the impetus to give up my dead-end job and resume my dream to make a living from that wonderful, difficult and downright impossible material that we all love – glass.
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