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My first slumping in a new mold produced a bowl with striations or fine scratches across its width. It's a rectangle about 11x5x1, and I held the slump for an hour. Too long? What could have caused these marks? It's 6mm of BE - also embedded 4 stringers in a rectangular pattern in the fusing phase. Maybe they affected the slumping process? Thanks for any help.

Do you have your complete firing schedule? Or at least the temperature you fired to.

A photo would also help.

An inch thick comes with plenty of the force of gravity. Your surface reflects the surface of the mold. Next time try rubbing lightly with your fingers to even out the mold texture, after the wash is dry.

The firing schedule was 300dph to 1100, hold 15; 100-1150-60; afap-900-45; 150-750-0; afap-100-0. The lines are very fine and parallel to each other-some are clustered about midway within the piece and some more toward one end. They are so fine that I doubt if I can photo them but I will try.

The lines are just on the upper surface so I wonder if the texture of the kiln wash caused them. In one place one line actually feels a little sharp, so maybe they formed toward the end of the firing. The bottom of the bowl looks like it was in contact with the mold for a while, but that's just a guess.

Just a quick clarification of my 1st post, which may have been confusing ... The mold is 1" deep, and the glass I'm slumping is 6mm thick. Sorry if that wasn't clear.

Here is an image of a section of the lines. You may have to enlarge it to see them near the brightest part of the reflections. On second look, they show up pretty well.

Those look like glass cutter score marks to me. Did you score the glass and not actually run the score (break the glass along the score)?

The look too parallel and defined to me to be kiln wash marks.

You're right, they do look like score marks, but I didn't score the glass. In fact, the marks run perpendicular to the one score I made. I went back and looked at the glass sheet that I cut this piece off of and see no sign of score marks on it either. Weird!

xacto marks from cutting paper strips on top of the glass is my guess.