2 large air bubbles

[nansea121]

Dan tried to fuse 2 layers of glass last night which developed 2 large air bubbles. Any ideas why this happened? The slumped plate on the right side was one he did last year at a fast full fuse - 1465°F with a hold of 10 minutes.

The 2 layered one he did last night was done at a slow full fuse with a hold of 12 minutes and was fired onto a freshly kiln washed shelf. Would those extra 2 minute hold time cause those bubbles to happen?  Both plates are 10" in diameter. I think he did it at a slow fuse this time to get more of a soak.



Back side...

[Kev]

Moisture left in the kiln shelf would be my guess.

[nansea121]

The shelf was dried at 550°F for 10 minutes before he used it and let the kiln cool down on it's own.

[nansea121]

I forgot to say that both plates had a thin clear cap fused on top of the opal art glass.

[Glassic]

I see the solution as Papadom platter, Baja Oleck in the lefthole, pure and unadulterated red chilli sauce in the right, a few small papadoms ...and a Vindaloo curry on the other dish.

[nansea121]

...and a Vindaloo curry on the other dish.

Vindaloo curry...mmmm!

http://members.ozemail.com.au/~bassboy/vindaloo.htm I loooove papadoms!!! We used to make them on the wood stove up north  when my late husband and I lived in the Yukon:)

http://www.curryfrenzy.com/curry/html/how-to-make-poppadoms.html
Now I'm craving for some curry.

It could also look like part of the galaxy with 2 visitor planets, lol.

Still thinking about curry! ..hehe

[Audrey]

OOOOH. I as just looking at a recipe with curry a few minutes ago. But alas, my husband doesn't care for it (or most spices, unfortunately) so I can't go there.

[Ian]

Hi Nancy
can you post your firing schedule? That will help a lot
Ian

[nansea121]

With that last plate, the one with the 2 holes, he did the Auto-Mode, which is
250°/hr -   300°F - 10 min hold
400°/hr - 1465°F - 10 min hold
9999°/hr - 950°F - 60 min.
100°/hr -  800°F - 15 min hold.

The first slumped plate he did last year (same size, same 96COE glass) was also done in the Auto Mode but at a fast full fuse.
500°/hr  - 300°F - 10 min hold
800°/hr - 1465°F - 10 min hold
9999°/hr - 950°F - 30 min hold
175°/hr  - 800°F - 10 min hold

Would the difference between the fast and slow schedules be enough to cause those 2 big blisters?

[Stephen Richard]

With that last plate, the one with the 2 holes, he did the Auto-Mode, which is
250°/hr -   300°F - 10 min hold
400°/hr - 1465°F - 10 min hold
9999°/hr - 950°F - 60 min.
100°/hr -  800°F - 15 min hold.

The first slumped plate he did last year (same size, same 96COE glass) was also done in the Auto Mode but at a fast full fuse.
500°/hr  - 300°F - 10 min hold
800°/hr - 1465°F - 10 min hold
9999°/hr - 950°F - 30 min hold
175°/hr  - 800°F - 10 min hold

Would the difference between the fast and slow schedules be enough to cause those 2 big blisters?

Yes.  It is called heat work.  in the first it took a theoretical 2.05 hours to get to top temp.  In the second it took a theoretical 4.6 hours to get there.  Yes normally slower is better.  In both these cases there was no bubble squeeze to let any air out before you went to the faster part of the schedule.

The bubble squeeze would occur at around 650C with a 30min soak.  This allows the glass to relax slowly allowing the air to be expelled by the sinking glass before it sticks.  

The soak at ca. 150C does nothing other than compensate for an over quick advance in temperature.  Go a bit slower ca 200C all the way up to 650C before you start the quick portion of the schedule.

Other tips are on
http://glasstips.blogspot.com/
Steve

p.s. dump the pre-programmed schedules.  Work out what is best for you

[nansea121]

Thanks Steve! I'll pass this info to Dan. It seems that he should have went with the schedule he did with his first plate then.
For Dan's sake I'll make your temps over to °F.

650°C (1202°F)
150°C (302°F)
200°C (393°F)

If we were to make our own schedule, how would you suggest it should be to fuse those 2 layers of glass?

[Becki]

I agree with Steve on this one.  And I think that Dan was lucky with his first piece. Am I right in assuming that this is opal art glass?  Not smooth on the top side?  I never fire opal art, especially with a clear cap, without a bubble squeeze.

[nansea121]

I agree with Steve on this one.  And I think that Dan was lucky with his first piece. Am I right in assuming that this is opal art glass?  Not smooth on the top side?  I never fire opal art, especially with a clear cap, without a bubble squeeze.

Thanks Becki. Yes, it was spectrums opal art, smooth on the top side.

How should we put in the bubble squeeze...right before the 9999°F? What could that firing schedule look like?

[nansea121]

I'm thinking that it would have 5 segments instead of 4?

[Becki]

I personally would stick with a slower schedule but take the first ramp up to 1100F with a hold. then add the bubble squeeze (segment 2) from 1100F to 1250F at 50-75dph then move on to the rest of your schedule. Yes, it would be 5 segments.

[nansea121]

I personally would stick with a slower schedule but take the first ramp up to 1100F with a hold. then add the bubble squeeze (segment 2) from 1100F to 1250F at 50-75dph then move on to the rest of your schedule. Yes, it would be 5 segments.

What does dph mean? I just had a look in the manual and couldn't find that abbreviation.

[Becki]

degrees per hour

[Ian]

Where Stephen gave a ramp rate of 200c the conversion to Fahrenheit is 200C = 360F
Ian
 

[nansea121]

I'll try and see if I can write down a possible firing schedule for this and then you can tell me if I got the right idea.

[nansea121]

Where Stephen gave a ramp rate of 200c the conversion to Fahrenheit is 200C = 360F
Ian
 

The rest is correct? I'm in Microsoft word and I'll see if I'm making any heads or tails with this. Dan is as befuddled as I am, lol.