That's silver leaf which has discoloured in the heat.
It looks very, very like it might have been made by Charlie Meaker.
His work tends to be big, have the silver leaf discoloured and have strappy clear bits around the top. I've not seen this exact shape before. Charlie Meaker did train for a while at IoWSG, and is in "The Glasshouse Tree", having been there in 1978. He is, according to the catalogue from the exhibition "The Glasshouse and its Tree", currently director of the Inferno Glassworks, Bornholm, Denmark.
I've not seen a Charlie Meaker piece this shape before.