Devit & Vermiculite observation

[Mark Wright]

Two identical fusings and only one devitrified. Everything the same except for one vermiculite mold vs one Ceramguard mold.

1- Two identical molds from the Kickstarter program. One vermiculite. One Ceramaguard.
2- Both molds kiln washed and pre-fired to 1500 degrees.
3- Four pieces of Tekta cut from the same sheet of glass.
4- The four pieces of Tekta double stacked side by side in the kiln and taken to a full fuse.
5- Both molds side by side in the kiln, kiln paper on top, and then the two Tekta blanks on top of the paper.
6- Fused to a full fuse per the schedule provided.
7- The piece on the vermiculite mold is heavily devitrified especially near the edges. The Ceramaguard piece has a small ¼” of devit in one corner.

Seems to me the vermiculite was emitting an undesirable chemical.

[Rick Wilton]

7- The piece on the vermiculite mold is heavily devitrified especially near the edges. The Ceramaguard piece has a small ¼” of devit in one corner.

Seems to me the Ceramaguard was emitting an undesirable chemical.

I'd think it was the other way if the vermiculite piece was devitrified.

[Morganica]

I think I'd want a second test, vermiculite-only and Ceramaguard-only.

[Brad Walker]

Two identical fusings and only one devitrified. Everything the same except for one vermiculite mold vs one Ceramguard mold.

1- Two identical molds from the Kickstarter program. One vermiculite. One Ceramaguard.
2- Both molds kiln washed and pre-fired to 1500 degrees.
3- Four pieces of Tekta cut from the same sheet of glass.
4- The four pieces of Tekta double stacked side by side in the kiln and taken to a full fuse.
5- Both molds side by side in the kiln, kiln paper on top, and then the two Tekta blanks on top of the paper.
6- Fused to a full fuse per the schedule provided.
7- The piece on the vermiculite mold is heavily devitrified especially near the edges. The Ceramaguard piece has a small ¼” of devit in one corner.

Seems to me the vermiculite was emitting an undesirable chemical.

Did you both kiln wash and use thinfire? Was there a reason to use both? I've tested with both individually, but never both at the same time.

Was original firing on kiln washed shelf or thinfire shelf? How did you clean the Tekta before and after the initial firing?

I've seen some hazing (not really devitrification, because it was on the bottom of the piece, not the top) from some brands of vermiculite board, but not all brands. The brand we're using to make the molds hasn't shown the haze. I haven't seen devit on Ceramaguard or vermiculite board.

Was the Ceramaguard corner with the devit near the side of the kiln or in the middle, next to the other piece?

When I have used paper, it was Bullseye thinfire brand. Was that the paper you used?

I have fired to 1460F in most of my firings, but have gotten good results recently firing to 1440F. If it's devit, the lower temp will help with the devit. Some molds can work with a lower temp than 1440F.

Also, I don't recall if I've tested two layers of clear 3mm. It's usually one clear 3 mm paired with one another 3 mm color, fired clear down. Also tested with one layer of 6mm Tekta.

I've probably done around a hundred firings on these materials, so am definitely interested in the details of your experience.

[Warren Weiss]

Was the kiln vented to 1000 f?
Warren

[Mark Wright]

Two identical fusings and only one devitrified. Everything the same except for one vermiculite mold vs one Ceramguard mold.

1- Two identical molds from the Kickstarter program. One vermiculite. One Ceramaguard.
2- Both molds kiln washed and pre-fired to 1500 degrees.
3- Four pieces of Tekta cut from the same sheet of glass.
4- The four pieces of Tekta double stacked side by side in the kiln and taken to a full fuse.
5- Both molds side by side in the kiln, kiln paper on top, and then the two Tekta blanks on top of the paper.
6- Fused to a full fuse per the schedule provided.
7- The piece on the vermiculite mold is heavily devitrified especially near the edges. The Ceramaguard piece has a small ¼” of devit in one corner.

Seems to me the vermiculite was emitting an undesirable chemical.

Did you both kiln wash and use thinfire? Was there a reason to use both? I've tested with both individually, but never both at the same time.
I had already applied kiln wash when I remembered 1) The vermiculite needed to be pre-fired and, 2) it would be best to use thinfire on the vermiculite. At that point I decided to keep everything the same so both molds went into the kiln and were pre-fired at 1500. The kiln wash probably burned off at 1500 and so I used Bullseye thinfire on both molds.
Was original firing on kiln washed shelf or thinfire shelf? How did you clean the Tekta before and after the initial firing?
The fusing of the 3 mm Tekta pieces was on a kiln washed shelf. The glass was cleaned with running water and a dedicated cleaning sponge before and after firing.
I've seen some hazing (not really devitrification, because it was on the bottom of the piece, not the top) from some brands of vermiculite board, but not all brands. The brand we're using to make the molds hasn't shown the haze. I haven't seen devit on Ceramaguard or vermiculite board.

Was the Ceramaguard corner with the devit near the side of the kiln or in the middle, next to the other piece?
Don't know.

When I have used paper, it was Bullseye thinfire brand. Was that the paper you used?
Bullseye

I have fired to 1460F in most of my firings, but have gotten good results recently firing to 1440F. If it's devit, the lower temp will help with the devit. Some molds can work with a lower temp than 1440F.
My top programmed temperature is 1460. Don't know what it really is but it is where I program my Skutt for a full fuse.

Also, I don't recall if I've tested two layers of clear 3mm. It's usually one clear 3 mm paired with one another 3 mm color, fired clear down. Also tested with one layer of 6mm Tekta.

I've probably done around a hundred firings on these materials, so am definitely interested in the details of your experience.

[Brad Walker]

Mark, the vermiculite had already been pre-fired to 1650F, so while your prefiring didn't hurt it probably wasn't necessary. The Ceramaguard was not pre-fired, I've seldom found the need.

The reason about asking for the location of the devit on the Ceramaguard piece was to determine if it was possible fuming or some sort from the vermiculite (in which it would be on that side) or was devit from overheating the piece, in which case it would probably be on the element side. Shame you can't remember the orientation in the kiln.

My regular full fuse is 1480, so firing to 1460 in my kilns is a bit lower than regular. So if 1460 is your regular full fuse temp then try firing to 1440 or even lower -- you just want to pick up the texture from the mold. If you fire too hot (i.e., after texture has already been picked up), you'll likely devit.

[Mark Wright]

Brad, When I looked at the two pieces again I realized the paw print tells me the orientation of the glass. So I can answer your question.

Was the Ceramaguard corner with the devit near the side of the kiln or in the middle, next to the other piece?

Draw two 6" squares side by side with about 1/2" between them. The square on the left was the vermiculite mold that devitrified. The square on the right was the Ceramaguard mold and the small patch of devit was in the upper right hand corner. Not close to the vermiculite.

[Brad Walker]

Brad, When I looked at the two pieces again I realized the paw print tells me the orientation of the glass. So I can answer your question.

Was the Ceramaguard corner with the devit near the side of the kiln or in the middle, next to the other piece?

Draw two 6" squares side by side with about 1/2" between them. The square on the left was the vermiculite mold that devitrified. The square on the right was the Ceramaguard mold and the small patch of devit was in the upper right hand corner. Not close to the vermiculite.

Mark, I think the devit most likely came from being overfired. Basically, the glass goes into the mold, then just sits there staying hot until it devitrifies. The vermiculite is thicker so it happens faster there. Next time you try fire to a lower temperature, 1440 or even 1430. If you're watching the kiln, you can start cooling as soon it the pattern is up into the glass.

I've tested that mold in both vermiculite and Ceramaguard, didn't have a devit issue with either material. Of course my overall situation didn't exactly mirror yours, so it's possible it's something other than just too much heat, but I'd try again first and see if that works for you.

[Valerie Adams]

i never had devit problems with my glass during my 12 years of fusing. Bought a case of Tekta and the trouble started immediately, but intermittently.
Through plenty of research and experimentation, I've decided it was the Thinfire causing the problem, but only when I'm clear-capping with Tekta.
Since I didn't use Thinfire in every firing, it took me awhile to realize that was the culprit.

[JestersBaubles]

i never had devit problems with my glass during my 12 years of fusing. Bought a case of Tekta and the trouble started immediately, but intermittently.
Through plenty of research and experimentation, I've decided it was the Thinfire causing the problem, but only when I'm clear-capping with Tekta.
Since I didn't use Thinfire in every firing, it took me awhile to realize that was the culprit.

Sounds to me like the Tekta causing the problem .

Dana W.

[Valerie Adams]

i never had devit problems with my glass during my 12 years of fusing. Bought a case of Tekta and the trouble started immediately, but intermittently.
Through plenty of research and experimentation, I've decided it was the Thinfire causing the problem, but only when I'm clear-capping with Tekta.
Since I didn't use Thinfire in every firing, it took me awhile to realize that was the culprit.

Sounds to me like the Tekta causing the problem .

Dana W.

That's what I thought. I pushed back with Bullseye and we ran lots of tests, mostly with my cleaning method. My complaint was that the problem only began with the Tekta. I found plenty of others struggling with the same issue, and it always seemed to come down to Tekta + Thinfire. I can use Tekta with kiln wash only and it's fine, so that's what I do now.

[smallbitz]

I had also never had a problem with devit UNTIL I used Tekta with Thinfire. It wasn't always, which fooled me for quite a while, but I eventually figured it out. The only time I do have a problem, it when the two are combined.

[Valerie Adams]

I had also never had a problem with devit UNTIL I used Tekta with Thinfire. It wasn't always, which fooled me for quite a while, but I eventually figured it out. The only time I do have a problem, it when the two are combined.

Exactly! I was only using Thinfire because I felt kiln wash was too much of a hassle. Now, I just have enough shelves that I've always got a few prepped and ready to go.