A Mystery

[Jerry]

12X16" piece of standard float glass with a lace pattern of Thompson's enamel around the edges. First attempt at 1300; enamel didn't mature and when looking through the glass from the back the enamel appeas to have pulled the surface of the glass off like glue chip does. It was so bad that the glass actually fractured on one corner.

Second attempt to 1525; enamel maured but still did it's trick of pulling the upper surface of the glass off. The enamel pops off the surface in large chunks.

What's going on here?

Jerry

[Tom White]

It sounds like you may be using the wroong enamel for float glass. Thompson's lists medium temp, low expansion enamel for float glass.

Best wishes,
Tom in Texas

[Bert Weiss]

12X16" piece of standard float glass with a lace pattern of Thompson's enamel around the edges. First attempt at 1300; enamel didn't mature and when looking through the glass from the back the enamel appeas to have pulled the surface of the glass off like glue chip does. It was so bad that the glass actually fractured on one corner.

Second attempt to 1525; enamel maured but still did it's trick of pulling the upper surface of the glass off. The enamel pops off the surface in large chunks.

What's going on here?

Jerry

Incompatibility is what is going on. The enamels are higher expansion than the base glass, so they shrink and tear up the glass. Either you got frits mixed up or it just doesn't fit. Back in the 80's they were screwing up in their manufacturing process and I got incompatible enamels. I haven't gone back to working with them again.

1300 is only a tack fuse without much gloss for Thompson. 1525 is probably overfired. 1400 is maturing temp.

[Jerry]

Thanks guys. The only problem is I've been using this flavor frit on float glass more years than I'm willing to admit to. Usually it's encased between two layers of float. Are you suggesting that if it's just on top there is a coe problem?

Confused in Maine,
Jerry

[Bert Weiss]

Thanks guys. The only problem is I've been using this flavor frit on float glass more years than I'm willing to admit to. Usually it's encased between two layers of float. Are you suggesting that if it's just on top there is a coe problem?

Confused in Maine,
Jerry

Jerry

That is entirely possible. If the enamel is higher expansion than the float glass, it is putting the float in to a state of compression. Because there is equal force on both sides of the enamel, it actually makes the whole piece stronger. Without the opposite force on it, it could be incompatible.

My previous expereince with Thompson was that the same # product came through incompatible one time. However my guess is that the first paragraph is really your problem.