devit with red bullseye

[michelle1]

I have done six tests to try to avoid devitrification in fusing red bullseye on black bullseye. The black is fine but the red has a scummy, cloudy look around the edges and into the centre. I often read this board but am posting my first message in desperation! These are the schedules I used (in celcius - I'm in Australia):
temp rate
1. 250 240
2. 670 55
3. 670 35
4. 820 500
5. 510 1500
6. 510 35
7. 460 30
8. 400 60

then, as above but:
3. 670 55
5. 510 1999

then, as first but:
3. 700 40
4. 800 600
5. 510 1999

then,as first but:
4. 775 600

then, as first but:
2. 500 400
3. 700 40
4. 775 600

then, as first but:
4. 780 500
5. 510 1999

I would appreciate any feedback on this.
Thanks, Michelle

[Phil Brown]

the red has a scummy, cloudy look around the edges and into the centre.

Michelle,
Were your edges ground with a grinder by any chance? The frosty edge on glass that's been ground can easily devitrify. Then as it flattens it becomes a ring of devit at the edge of the glass. Don't know what size/shape glass you're working with so not sure if this would apply or not.

Phil

[Jerry Barnett]

Michelle,

I think Phil is right that grinding the edge increases the probability of getting devit with any glass, but with red opal this will occur with as-cut edges as well.

Seems to be the nature of the beast and, from its position, related to the interior of the red opal glass ending on the surface. I've had it occur with sheet glass, the end of stringers, and frit. I suspect that the surface glass is a slightly different chemistry than the interior.

I have found that refiring with an overspray has removed it. I use Super Spray because that is what I have. Other commercial oversprays may work as well. I have not tried pre-spraying with a borax solution before the initial fuse, but that might prevent it in the first place.

Jerry

[Cynthia]

Spray the work, making sure to cover the sides of your red pieces as well with an overglaze or flux such as SuperSpray or Borax solution. This should stop your devit problem.

Might want to avoid Spray A or other lead bearing overglaze/fluxes because the lead can react with some glasses and give you a brown stain.

Some BE opals just seem to be prone to devit in my universe, so I use Super Spray on everything for that first firing.

Avoid getting it between layers of transparents. It leaves a milky stain if sandwiched that you can see through transparents.

[Mike Byers]

I've encountered devit with red and cobalt blue Bullseye stringer, but not with the sheet glass. This probably reflects the temperatures I'm using. The stringer seems to devit evenly, which results in a matt surface. This seems to happen only at temperatures above 1400F or so in my kiln. I was wondering if it would be possible to spray just the stringer with borax, etc., or would the entire piece need to be sprayed?