Devitrification, any fix after the fact?

[sherrieb]

Hi all,

still having fun with the new kiln (Caldera) and I was fusing some small jewelry pieces this time.  Pieces on top shelf were fine, but most on bottom shelf have the “scum” on them.  I’ve checked into the causes of this, and perhaps I didn’t get them clean enough (would shelf lying on the kiln floor contribute?).  Is there any way to correct it on those pieces, though, or are they garbage at this point?  If garbage, does that mean just throw them out, or can I reuse in a pot melt or break them up to add to something else later?

thanks,

SherrieB

[Anonymous]

 Sandblast and fire polish.

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Paul
FusedGlass.Org
Helios Kiln Glass Studio
PaulTarlow.com

 

[sherrieb]

Thanks Paul!

 

SherrieB

[Caren Johnson]

This is an interesting subject because I have been firing some rather large pieces, and they break if cooled too quickly. I am having a hard time deciding how to cool them more slowly withoug risking devitirfication as well. And in your experience, fusers, would the devitification spray prevent both these occurrences? Thanks, Caren

[bookie13]

Hi Sherry,

Devit on cabs is usually caused by your not grinding the edge fine enough. Many people use a 120 grit bit to grind their cabs. If you fuse those, you will get scum. You need to grind much finer (320 minimum) and then add a light coating of some devit agent (spray A, clearcoat, etc).

As to cooling, devit forms above 1200°F. thermal shock happens below 1000°F. So if you crash your kiln below1200 you will not have to worry about adding to the potential of devit. Having said that, most of the major glass manufacturers’ glass is devit resistant and will not likely have devit unless you are doing multiple firings or firing very high.

 

Barry

Barry Kaiser

Web Site    http://www.kaiserglass.com

Glass Classes:   http://www.Kaiserglass.com/classes.html

Tutorials      http://www.kaiserglass.com/tutorials.html

[Caren Johnson]

Thanks Barry,

This site is so helpful! You all are so willing to share your experiences and knowledge!
Caren

[sherrieb]

Thanks Barry!

SherrieB

[Anonymous]

Bullseye just sent out a tech tip that suggests sifting a very thin layer (really just enough to cover the surface) of 1401 crystal clear powder and refiring to about 1435f for 10 minutes. Just tried it and worked great.

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Paul
FusedGlass.Org
Helios Kiln Glass Studio
PaulTarlow.com

 

[sherrieb]

Thanks Paul, I will try that.  My husband swears we have a sandblaster, but knows not where…

 

SherrieB

[Anonymous]

Wow – cannot imagine losing a sandblaster – they are usually huge

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Paul
FusedGlass.Org
Helios Kiln Glass Studio
PaulTarlow.com

 

[tzirlen]

What did you use to sift that thin layer of powder?  I tried this fix and my results weren’t great because I couldn’t get that thin, even layer I was looking for.  Thanks!

[thomas decker]

you  can also use an eching cream and than re fire I have used etch all but any etching cream should work.

I have done this several times and it works really well , just make sure that you clean the piece very well after you  etch the glass , It’s like sandblasting without the blaster. )

Thomas Decker

[WackyPup]

I also have a caldera, & I would love to know how you’re getting two shelves in it. Are they 7 inch shelves? Do you have them staggered? When I tried two shelves the top shelf and bottom shelf were two totally different fusing experiences

[freebeaches]

After the tak of flowers and islands and a moon on to the base of green field, the field shows devitrification. 🙁 I did use spray A and still got divit on the base of green but not on the many flowers. Is there any way to get rid of the divit on the green field? I cannot sift clear because I would have to fire up to 1400 and that temp would loose the definition of the components. boo hoo… any help would be greatly appreciated.

[bigtexun]

I use whatever cold-work tooling that is appropriate, if the pieces are large enough to handle. So far I have a pneumatic wet grinder, and I also use emery paper from home depot, as well as a regular dry belt sander. A sand blaster and a wet belt grinder is on my Christmas list for NEXT year (this year I bought a house with a detached studio for Christmas).

Devit can be very severe if you have some cheap glass with questionable origins, so I try to cap those with a reliable clear thin (or a dusting of clear frit). I am surprised at hearing people fix it rather than removing it and doing a fire polish (or cold work polish). Obviously if you have questionable glass, you should do a compatibility test to confirm you can mix your clear with it successfully.

And yes, dirty glass can appear as devit. Even residues that will disappear completely in firing can leave residue marks. Things like stickers or sharpie ink on the glass and even tape residues will leave marks if not cleaned off first.

[Author]

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