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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

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

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

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.

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.

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.

Charlie's right. Sandblast and firepolish again... OR, sandblast then slump which will give you a matte finish.

Tony

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.

Looks like production line belts moving the still warm ( hot?) glass around the plant. Seems way to regular to be anything else. I've had marks on some BE clear also, but not as nice as yours

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

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.

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

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

I have had the same devit pattern with BE clear. My solution was to polish the devit out.

Tim