Andy Dingley brought next idea :
Big shears (ideally a big guillotine) and do it under water to damp
vibration. A lot depends on the quality of your mica. Where did you
find it BTW, and how big do they have it?

Ebay I ordered 4x4, but they list 5x5. The price rises rapidly with
size.

Heatproof glass windows are available easily from the suppliers for
enclosed coal stoves, Expect to pay about 40 quid though, and you'll
need some glass fibre webbing to put it in with too.

I don't think they do it with a gas bottle curve :-)

--
Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk