Project of the Month: September 2021

4. It’s all in the temperature

This is my kiln now so everything kilnwise has ground to a halt. I was going to invest in another two kilns anyway, the both to be used exclusively for pottery, a standard pottery kiln and a raku kiln. One of which is already on order. This one I’ll reserve for glass fusing and small items of pottery once it’s repairs.

It transpires that my neighbour of over 5 years used to work with glass all the time. One of his first jobs was for British Aerospace. During his time with them he worked of a range of aircraft windows including the canopies for restoring Spitfires. I was fascinated to learn that they had to use exactly the same methods and tools following my recent visits to the Shuttleworth Collection.

Spitfire at Shuttleworth Collection

Apparently they heated a sheet of glass to about 650° and as it began to slump into shape a team of workers went into the room to hammer the glass to the frame and then left to allow the glass to cool down slowly. If, at any point the room got too cold to fast, the glass would cloud over to become opaque, and if the room was opened after firing and a draft cooled it too fast the canopy would shatter. During WWII the success rate was just 50%.

He confirmed things I was learning the hard way through trial and error such as why clear glass will turn opaque after firing and that the more you fire a piece of glass the harder it becomes to slump it again which is how I ended up fusing glass to one of my moulds. I might be lucky if I turn it upside down and l leave it to fire at a high temperature for a long time, but I doubt it.

I intend to switch to using stainless steel bowls which are a lot cheaper to replace until I get the hang of this. I also will also try shaping some stainless steel mesh covered with kiln fibre sheets once the kiln is repaired. At that point my neighbour has kindly offered to do a fuse firing with me to get the firing temperatures just right.

As for my project this month, I conclude with an attempt using the pouring method with the upturned mould concealed in an upturned flower pot and another flower pot placed on top. The glass flows through the holes of both pots. You do have to ensure that everything the glass will touch is coated with batt wash or covered with kiln fibre, but yes, it worked.