Devit on draped bowls

[wharrel]

I have draped some bowls on stainless steel molds. Some of the bowls have patches of devitrification. I tried to put homemade devitrification fluid on them and then fire polish them at 1115 for 10 minutes. The bowl slumped a little out of shape but the devit was still there. At 1115 I thought there would be no slumping but there was so I can't raise temp to firepolish without slumping the bowl out of shape. Before I ever draped the bowls they were sprayed with devitrification fluid and dried. When I first started draping I stopped at 1150 for 1 hour for bubble squeeze. I believe this was the cause of the devit. I reduced bubble squeeze temp to 1125 for 25 minutes and had no more bowls devitrifying.

Fire polish
125 1115 10
full 955 45
0000

Drape
125 1125 25
125 1300 30
full 950 45
0000

Thanks in advance for any help. Bill Harrell

[JestersBaubles]

Devit temp is usually higher than slumping temps. Also, there is no need for a bubble squeeze -- which usually occurs at about 1250 deg F -- when you are draping. A bubble squeeze is used when you are fusing two pieces of glass together.

What did you coat the stainless steel mold with? Is the "devit" on the side that touched the mold? If so, my guess is that you are seeing hazing from the boron nitride product. If you are using Hi-Temp 1800, throw it away and get some MR-97.

Dana W.

[JestersBaubles]

I just looked at your schedule a little more closely. At least in my kiln, 1300 deg F is pretty hot for a drape.

Dana W.

[Morganica]

Are you sure you've got devit? Sometimes draping can compress some areas of the glass surface, which produces a kind of hazy appearance.

[wharrel]

Jestersbaubles--
I spray Bullseye kiln wash when mold is about 500 degrees. I also put 1 sheet of shelf paper and run the kiln to 1000 before I take the vent out. I drape 2 ea 1/8 inch spectrum glass with elmer's glue to hold them together so they have to fuse tack together, but bubbles are not that bad. Devit is mostly on the outside of the glass. Thanks for your advice-Bill Harrell

[wharrel]

Morgancia---
I am draping 2ea 1/8 in Spectrum glass coe unk. The 2 pieces are 6 in. squares offset 90 degrees which make 8 triangle peaks. I glue tiny bits of glass in four places on the sheets to provide a path for air to evacuate. The glue is Elmer's clear.The outside of the peaks is where most of the devit(?) occurs. The devit is hazy and rough. The devit stopped occurring on later bowls when I reduced the bubble squeeze time and temp. So I don't know if it is actually devit or some other type of haze. I have tried polishing the glass with car paint compound but it does not help. I am wondering if I use a torch to heat the actual devit area. There is a chance of breakage, but I will try first on a cracked piece. Thanks for your interest and help- Bill Harrell

[Glass Fever]

I'm a little unclear on if you are fusing your blank first and then draping, or are you trying to do it all in one step. I would fuse the blank first, and then drape. Then as already mentioned there is no reason for a bubble squeeze during the drape firing.

And yes if you try to heat cold glass with a torch it will thermal shock and break.

[wharrel]

Glass fever,
I am fusing the 2 sheets of glass and draping at the same time. I will now fuse first then drape. Thank you for your interest- Bill Harrell