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cool devit...and how to get rid of it
Posted: Wed Oct 01, 2003 11:43 am
by lissa
I have a 13" disc 1/4" thick that developed devitrification in a an attempt to fire polish. I brought the piece to full fuse, no problem, and then flipped it and set a fire polish cycle as I wanted the 'top' to become the 'bottom'. Devitrification developed on BE transparent orange and black in a very precise geometric pattern, almost like a sneaker print. It had been thoroughly cleaned, and we have no surfaces in the studio or house that look like the pattern that developed. Any insights???
One part of the piece has been through a lot of firings now, and I am a bit concerned it may crack so I want to be gentle, but I would like to try and save the piece. I have a lot of time invested in it. I don't have sandblasting capabilities, but could take it some where. Should I sandblast and then slump, or should I coat with borax or superspray and try another fire polish? Will the sandblasted surface need to be fire polished or will the slump cycle gloss it up a bit?
Thanks for any help on this, or any insights on the weird devitrification.
lissa
Posted: Wed Oct 01, 2003 11:57 am
by Barbara Muth
Had the bottom been on a kiln washed shelf? I have found occassionally that even though I thought I had gotten the glass very clean, when I flipped and fired, after the fuse I saw lines which must have been kilnwash. My solution has been either to sandblast it clean and fire again, to live with it as is, or to avoid it happening by firing on thinfire.
Barbara
Re: cool devit...and how to get rid of it
Posted: Wed Oct 01, 2003 12:06 pm
by Tony Smith
lissa wrote:I have a 13" disc 1/4" thick that developed devitrification in a an attempt to fire polish. I brought the piece to full fuse, no problem, and then flipped it and set a fire polish cycle as I wanted the 'top' to become the 'bottom'. Devitrification developed on BE transparent orange and black in a very precise geometric pattern, almost like a sneaker print. It had been thoroughly cleaned, and we have no surfaces in the studio or house that look like the pattern that developed. Any insights???
Is there a chance that your kilnshelf had been stepped on? It's amazing the contamination that can be transferred to your glass from the shelf.
Tony
Posted: Wed Oct 01, 2003 12:36 pm
by charlie
you'll have to sandblast it. slumping temps won't make it shiny again, you'll have to firepolish it. a slump temp of 1225 on a sandblasted surface will leave a very fine matte finish.
Posted: Wed Oct 01, 2003 12:39 pm
by lissa
Nope, not stepped on, and it shows up just in certain areas on pieces, but must be some sort of shelf contamination. Maybe I can post a picture. So would you recommend having it sandblasted?
thanks, lissa.
Posted: Wed Oct 01, 2003 12:42 pm
by lissa
Thanks Charlie, I missed your post. I'll call the sandblaster today. What would be a good firing schedule for the fire polish, I obviously botched it the first time!
lissa.
Posted: Wed Oct 01, 2003 12:42 pm
by Tony Smith
Charlie's right. Sandblast and firepolish again... OR, sandblast then slump which will give you a matte finish.
Tony
Mystery solved...mostly
Posted: Wed Oct 01, 2003 8:41 pm
by lissa
I have been racking my brain as to what contaminated my shelf or glass to get this crazy devit pattern, and then this evening in the studio I picked up a fresh piece of BE gold purple and lo and behold....THE PATTERN!

on the black glass

on the transparent orange glass
On the bottom/bumpy side of the glass the same pattern appeared but as darker in color, obviously not devit. I assume this is from a rack or something the glass is on during processing? I am wondering is there is inherent stress in these markings which made that glass prone to devitrification and perhaps other problems or weaknesses?
At least I can stop wondering what it was that caused the pattern.
Again, anyone willing to share a good and gentle firepolish schedule so I don't second these results? Should I borax it before fire polishing?
thanks! lissa.
Posted: Wed Oct 01, 2003 9:39 pm
by Clifford Ross
Posted: Wed Oct 01, 2003 9:43 pm
by Brock
It looks like that glass went into the lehr too hot. Those appear to be the marks of the chain belts that transport the glass through the lehr. Brock
Posted: Thu Oct 02, 2003 7:36 am
by lissa
Why would devitrification develop there? Is there more stress in those areas already?
I wonder if I should not use this batch of gold purple I have, the side with the pattern will have to be the top of the piece to have smooth sides together. Hmmm, but it appeared on other colors as well. Just more careful firing perhaps.
lissa.
Posted: Fri Oct 03, 2003 4:37 am
by Brian and Jenny Blanthorn
lissa wrote:Why would devitrification develop there? Is there more stress in those areas already?
I wonder if I should not use this batch of gold purple I have, the side with the pattern will have to be the top of the piece to have smooth sides together. Hmmm, but it appeared on other colors as well. Just more careful firing perhaps.
lissa.
Devit is a very big subject
But in brief
Any part of the glass scratched / dirty / got stuff on etc will devit given the correct conditions
U C the glass is in a liquid form n just itching 2 cristalise
But it cant cristalise from nothing its gotta have something 2 grow from
This is something not liquid like say sand or scratched glass
This is called a neucleation point
The anti devit stuff works by disolving the neucleation point or and making the surrounding glass 2 liquid 2 cristalise
Devit will only grow above softening n stops when it gets runny
Me n my buddies have written a lot on this all in the archives
Brian
Posted: Fri Oct 03, 2003 4:37 am
by Brian and Jenny Blanthorn
lissa wrote:Why would devitrification develop there? Is there more stress in those areas already?
I wonder if I should not use this batch of gold purple I have, the side with the pattern will have to be the top of the piece to have smooth sides together. Hmmm, but it appeared on other colors as well. Just more careful firing perhaps.
lissa.
Devit is a very big subject
But in brief
Any part of the glass scratched / dirty / got stuff on etc will devit given the correct conditions
U C the glass is in a liquid form n just itching 2 cristalise
But it cant cristalise from nothing its gotta have something 2 grow from
This is something not liquid like say sand or scratched glass
This is called a neucleation point
The anti devit stuff works by disolving the neucleation point or and making the surrounding glass 2 liquid 2 cristalise
Devit will only grow above softening n stops when it gets runny
Me n my buddies have written a lot on this all in the archives
Another thing U could do is get the glass realy hot n disolve the devit
Brian
Posted: Sat Oct 04, 2003 11:42 pm
by Tim Swann
I have had the same devit pattern with BE clear. My solution was to polish the devit out.
Tim