Help with float glass

[Martman]

Hi all
I have a firebox 14 and I'm trying to fuse 3 layers of 2mm float glass top temp 835c for 15 mins.  I have tried with 9 sets of 3 layers  90mm square, what is happening is that on some of the sets the top layer corners are curling up and you can see the 3 layers where they have not fully flowed.  On some, the top two layers have fused with the bottom one but the corners of the bottom layer remained square. And on some the glass has defrication, white all over.
I have even tried with one piece of 6mm float that was better but the corners at the base remained square.
Theses were fired on thinfire.

Any ideas

Mart

[flame n fuse]

sorry, I can't help, your temperature doesn't sound right. Have you tried this forum ...http://www.warmglass.com/

[Zeldazog]

Mart, it would help if you gave your full firing schedule, aside from the fact I assume you've made a typo in saying top temperature 135c, fusing is about the whole cycle, not just the top fusing temperature

Float glass is quite prone to devitrification anyway, and the overall program, such as the rate of climb, could have a bearing on that (how long its in the devit zone) - you have to be absolutely scrupulous with cleaning float (any glass really, but float will show anything as scummy marks) - you may also have tin bloom

Can you show us some photographs as well?

[Martman]

Thanks Zeldazog

I have amended the typo 835c will up load the schedule later.

Martman

[Martman]

Zaldazog

pictures are here http://www.flickr.com/photos/78893017@N03/

Schedule was
R1 121 T 593 H 15
R2 93  T 674  H 40
R3 full  T 821 H 15
R4 full  T 593 H 35
R5 66   T 482 H 1
R6 full   T 20  H 0

MartMan

[chas]

Hi MartMan, my kiln is different, and as you'll see elsewhere, the kiln/programmer/glass type variations all conspire to thwart... I can only suggest further experimentation.
For what it's worth, our float "full fuse" is below. 6mm total thickness is within our normal operating range. Our programmer works on "time to achieve temperature", so you'll need to work out the rate if that's what yours asks for:

3 hours to 677c, hold 30mins
30 mins up to 833c, hold 15 mins
asap down to 482c, hold 1 hour
1 hour 45 mins down to 371c, kiln off and natural cool

Chas

[Zeldazog]

Martman, I full fuse float glass at around 840 (I think the guide I first used was 843C), without checking the kiln I can't say what it's set at now, your schedule says process temp at 821, float wouldnt' full fuse there I don't think.

Your rate 2 hold is quite long, I think you might *just* be in the devitrification zone, so that could be the "whiteness" you describe, although looking at the picture of the triple layer, is it possible the glass is K-glass at all?  Did you buy it, or take it as scrap?  It looks as though its a possibly a treated glass?

Also, your Rate 5 isn't going low enough - I, like Chas, do my controlled cool down, through the annealing zone, down to 371 (although I start at 517) - 482 isn't low enough to finish annealing at I don't think (not that this would have a bearing on the final effect, just that your glass won't be annealed)

[chas]

Also, your Rate 5 isn't going low enough - I, like Chas, do my controlled cool down, through the annealing zone, down to 371 (although I start at 517) - 482 isn't low enough to finish annealing at I don't think (not that this would have a bearing on the final effect, just that your glass won't be annealed)

Hi Zeldazog, I guess I've never given the 'downside' of the fusing schedule quite the same attention of the 'upside' - getting the stuff to behave and soften is a pre-occupation.
So, could you give us your full schedule - and to make it absolutely clear, indicate the annealing section and from what point it's just 'kiln off and cool down asap'?

Cheers,

Chas

[Zeldazog]

Annealing is an important part of working with glass, whether you're lampworking, fusing, casting or blowing, etc  Without it, the glass has stresses - it might not crack immediately as it comes out of the kiln, it might be stable for a matter of months, I've even heard years, but one day a crack can simply appear in glass that hasn't been annealed properly.

through the annealing zone, down to 371 (although I start at 517) -

this is my annealing section, I always used the Bullseye range as I couldn't be bothered to keep re-programming every section each time I changed what glass I put in.  The cool down rate within this zone can vary depending on thickness of glass, size of piece, etc, but the one you've used Chas, (without getting out the calculator and working out the rate) looks fine to me.

I refined my firing by gathering together all the schedules I could find, from forums, internet, books  - there's a lot of variables, depending on glass, thickness, size, artist - although the annealing section is usually pretty consistent, and of course, the kiln itself.  I then experimented with small sections of glass until I found the schedules that suited my purpose, whether I wanted a full fuse, a tack fuse, etc.

It took quite a bit of research and a lot of time, but it allowed me to get to know the glass and the kiln.  The information is out there - try the Bullsye site, there tipsheets are invaluable as a starting point, and Warm Glass forum, the US one has a lot of info in it.  Within that forum is the Warm Tips section, by Brad Walker who also wrote Contemporary Fused Glass, which is a really useful book IMO.

HTH

Dawn