It looks like you are

Stephen Richard

It looks like you are bending this piece of glass.  Is that right?

Are the marks on the top or bottom? You are bending over a mould, yes?

It sounds to me like you are bending over a form because the marks increase with temperture. Therefore the marks must be from contact with the mould.

Most glass bending takes place as a slump.  This takes advantage of the weight to pull the centre down.  It means you can bend your glass at as little as 570C with sufficient time.  This avoids marks from the mould.  If it is a free curve, it can even be done without a mould, just supports along each edge, about 50mm in from the edges.  You need to cut off the extra after firing, of course.

You can get some more information from the two blogs listed below.

Stephen Richard

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