BE vs Urboros clear glass 90 coe

[Stacey Jones]

I recently did two test pieces in my skutt coffin kiln. One was with two sheets of BE, the other with two sheets of Uroboros. Both of them had 3/4 inch squares of a variety of colors on them. Fired slowly , held 1 hour @ 1250, up to 1400. Ramped down with a 1 hour hold @ 960. Both pieces came out fine, except that BE had lots of tiny airbubbles as usual, and Urboros had a number of large spread out airbubbles - very irregular.

This is my first time using Urboros. the clearness is very attractive. the finished product wasn't, in this case. Any ideas?
Thanks in advance
Stacey

[Lynne Chappell]

I use the Uroboros machine rolled clear pretty much exclusively now. When I first switched, I did notice that they melted a little differently. The handrolled BE seems to be a little "softer". Probably the big difference in what you're doing though is the smoothness. Less little bubbles trapped, but potential for major air traps. I'm assuming the bubbles are between the layers. I think a hold at 1250 is perhaps too high, the glass may have already softened at the edges. I do a squeeze at 50F per hour from 1150 to 1250 and have little problem. However, I do fire to a higher temperature (1480F for 10 minutes). If I get bubbles (not volcanoes, but larger than are attractive), they seem to settle out at the higher temperature. If I only fire to 1460, sometimes there are bumps on the surface (particularly unattractive on black glass).

The other problem may be your design. I've had issues when I have areas of extra thickness, especially things like squares placed on top with small spaces between. My theory is that the extra weight pushes down on the softening glass leaving gaps between.

[Carla Fox]

I too, notice that the Uro clear (the only uro I use) is prone to big misshappen bubbles, while the BE in the same load, has nice little champagne bubbles. I haven't bothered to work out a schedule to fix the problem. I'm going back to the BE clear.

Carla

[Stacey Jones]

For the majority of my work, anything over 1400 ruins the effect I am trying to achieve. I guess I'll stick with BE clear. I did notice that Urboros firing schedule is a bit higher than BE. Thanks for the replies!
Stacey