Stretch Marks?

[smallbitz]

This seems to happen to me frequently when I slump with clear glass. It almost looks like stretch marks. This is a very shallow plate mold - no more than 1/4" deep. It was 96 glass with pattern bar inserts that had been full fused, cold worked and fire polished. My slump schedule was as follows:

150-1000-10'
50-1120-60' (before it slumped all the way)
full-950-60'
200-800
300-600

Here is a photo - very hard to get a pic of what I call the 'stretch marks' but I did my best. All of 'stretch' is on the bottom lip and vertical edges. Any comments or advise would be much appreciated!

[Kevin Midgley]

Stretch marks are common in float glass that has not been for lack of a better term, cooked long enough in the manufacturing process as that costs money.

You can't tell by looking at it prior to firing it.
As you've found, fusing it will result in good results but forming causes the issue.
The only answer I've found is to use a better or different glass.
The results can be beautiful but sometimes not so.

Perhaps another reason to use Bullseye glass?

[Marty]

Irid?

[Jerrwel]

Stretch marks are common in float glass that has not been for lack of a better term, cooked long enough in the manufacturing process as that costs money.

You can't tell by looking at it prior to firing it.
As you've found, fusing it will result in good results but forming causes the issue.
The only answer I've found is to use a better or different glass.
The results can be beautiful but sometimes not so.

Perhaps another reason to use Bullseye glass?

Per Brad's suggestion, I fire my Bullseye strikers to 1350F to get the color developed before I even store them so there is no confusion with colors. I wonder if firing 'cheaper' glass in this manner before using it in a project would help this 'half baked' glass issue.....wondering. Prefiring the glass would probably be cheaper than buying more expensive glass if it works.

[smallbitz]

No, not irid. I use both 96 and Bullseye. I'm going to look back through my notes and see if this has ever happened with the 90 before. Curious.