devitrification

[Helen]

Hello, having always used System96 and float, I've just used Bullseye glass for the first time and fused a 280mm sq plate, 6mm thick, in white, cranberry and orange. The white and cranberry parts have devitrified but the orange in the centre is ok. Can anyone advise me if it's possible to rectify this?  I wondered if it might clear when slumped.  I'd appreciate suggestions, thanks.

[AnnaSpanna]

am pretty sure that de-vit is somewhat irreversible. You might get a slight reduction of scumming/crusting if you slump it but its unlikely. Devitrification is when the glass is no longer "glass" and has become a crystal form. All glass has a devit zone and the temp varies and the amount of devitrification depends on how long the glass was in that zone (usually when cooling down). Bullseye have really good info pages on all their glasses and how it acts at certain temps. You may be able to find something in their site that will explain a. what colours are likely to devit and at what temp (thus you can avoid the devit zone and minimise it happening again) and also how to rectify or minimise the scuzzing that you now have (can I coin a new technical term?). This gambit of useless info is prob not going to help with your current dilema but as I said bullseye have really great technicians and spotters working for them and so should be able to offer advice.

[Helen]

Thanks Anna, I should have started small with Bullseye but I was following one of their firing schedules and took a chance. It's so true that I should get to know my kiln better before I try anything that matters!
Helen

[firedinglass]

Sorry to have to agree but the devit will almost definately be irreversible...

[Zeldazog]

Whilst it's true that you cannot really reverse de-vitrification, If you have access to a sandblaster, you could try blasting the top surface to remove the scum, and then back in the kiln to fire polish it.

I have found a couple of colours seem to be more prone to de-vit than others, but often I get it a occuring at edges of different colours, which tells me I didn't clean the glass as meticulously as I should have done, and that can cause the scummy effect too.

[Warm Glass UK]

Hi Helen - Devit is rare in Bullseye Glass, but when it happens at fusing temperatures is almost always down to the cleaning process used. We find that glass cleaner and paper towel work best. Never use any type of detergent, meths or neat acetone. Solving the issue will depend on a number of things, including the type of kiln you are using. Please feel free to contact me on 01934 863344 if you have any issues with Bullseye Glass.

The piece you have will need to be sandblasted (only on the top side) and then re fired, this will give you a perfect finish.

Again, please feel free to contact me on 01934 863344 if you have any issues with Bullseye Glass.

Good Luck. Simon-Warm Glass UK

[Helen]

Thanks everyone for your helpful information. After reading advice it looks like I could have cleaned the glass better and I'll definitely try sandblasting and re-firing.  There's hope yet! Thanks again.

[Flippopotamus]

Hi Helen,
I've successfully 'de-devitrified' (should that be 're-vitrified') a couple of Bullseye plates by sifting a layer of crystal clear frit powder uniformly across the piece & then re-fusing at full fuse temp.  This gives a great shiny finish - with the light shining at the right angle I can still see the devit layer sandwiched between, but it looks much more like a feature than an error.

This ebay seller is honestly nothing to do with me, but they do give great service & are really good for small urgent orders, like 50g of crystal clear frit powder!
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=150421244981&ssPageName=STRK:MEWNX:IT

Cheers,
Flip

[Lucas]

Just to second the recommendation above, I've used them a few times and orders have always come very quickly and well packaged, and one time something had been left out and I rang them, feeling a bit dodgy as I thought they'd think I was making it up, but they sent on the missing item and a little freebie to make up for it not being in there in the first place!
Out of interest, what would the firing schedule be to fire polish 6mm bullseye?
Lucas

[julieHB]

Warm Glass has summarised a lot of information from bullseye in this excellent one-page overview:

http://www.warm-glass.co.uk/Downloads/Public/Products/Tools/Basic%20Firing%20Schedules%20for%20most%20kilns.pdf

You find many of the bullseye technical articles on their site as well, or you can visit www.bullseyeglass.com

[Zeldazog]

Oh, Julie, that's a great find,  I have all the other sheets, but that's great to be all in one place, thanks for the link - I hadn't seen that one

[julieHB]

Isn't is just!! I have had a worn out print-out for a looong time, couldn't remember where I found it....and then one day last week I was determined to have a long and thorough look, and yay! results 

[Lucas]

Fantastic - thanks Julie!  Now to add printer paper to my ever expanding shopping list!
L

[Black Heart Beads]

Thanks from me also Julie. I have most of the info already but on various bits of paper, so its good to have it all together.

[Carl]

A recent bit of glass of came out of the kiln in a less than shiny state, thanks to this thread I now not only understand why but also how to cure it. Thanks all for the advice and special thanks  to warm glass for providing free of charge the main component to my new sandblasting cabinet 

Untitled by carl.grigg, on Flickr