Trapped air - help please!

[Peego]

Hi
I fired 6 coasters yesterday with inclusions of glassline paper and/or copper foil, nearly all of them had a massive air bubble trapped in the middle at least 2-3cm across. One bubble exploded and broke through the top of the coaster.  I used tekta glass coaster pieces and put the smooth sides together, should I have put the rippled sides together to allow for some air to escape? Should I use some clear stringers to the edge, would that help? Any suggestions will be greatly appreciated as I want to try again later this week.
Thank you

[Krysia@No98]

You will be more likely to get bubbles using metals. The glass is more likely to move too.

Was the foil absolutely flat?

Was the foil clean?

what else did you put between the glass?

[Peego]

The foil was flat but a little crinkled in places, I had handled the foil, how do I clean it?  I layered the foil over the top of a piece of glassline paper.

Thanks

[SilverGems89]

What's the schedule you fired on?

[Krysia@No98]

It could be the two things together...

I wash all the glass before I use it, just with washing up liquid and then dry it of and then try and handle it with paper.  I guess that last bit won't make a lot of difference. 

Maybe wash the foil as well, it can't hurt.

[Peego]

I fire up to 677 degree c over 3 hours and then hold for 30 mins, then quickly up to 800 (takes 20 mins) then hold for 10 mins, then quickly down to 516 usually takes about an hour then slowly cool down.  Can you see naything in this that would cause bubbles or could I change it slightly to eliminate them?  will try washing foil too.

Thanks

[MeadMoon]

I use a fairly similar schedule to that, except that from 677 to 804 my rate is 333 rather than ASAP.  Actually, that is about 20 minutes, so maybe you're doing the same.  You could tweak the firing schedule by reducing the first rate (from room temp. to 677) to 150/hour or even lower,  and increasing the first hold (at 677 degrees).

Bear in mind that every kiln is different, so you need to work out what works for your kiln.

Other things to think about - copper foil does give bubbles, so the thickness and size of the piece of foil can make a difference.  Thinner foil makes more bubbles than thicker foil. Someone recently mentioned using stringers to form channels for air to escape and I've also seen that you can put small pieces of frit in the corners between layers, but I've not tried either of these myself.

Take a look at Bullseye TechNotes No. 5 on Volume & Bubble Control for further info: http://www.bullseyeglass.com/methods-ideas/technotes-5-volume-a-bubble-control.html

[Peego]

Thanks for your help, much appreciated, will try the frit method too.

[flame n fuse]

677 may be a bit on the hot side for a bubble squeeze (it depends on your kiln), try dropping the temp to about 650. & I do recommend using stringers - I made big bathroom tiles with a frit design between the layers and had trouble with bubbles till I tried the stringer trick.

[Peego]

Thanks am gonna order some clear stringers now and will lower the temp. Will let you know how I get on. Much appreciated.

[Glyn Burton]

You could just pull a few stringers from scraps of tekta to try it out before you go to the trouble of ordering some.

[Peego]

Hi
Am fairly new to all this, how do I go about pulling stringers from scraps of tekta?
Thanks

[Zeldazog]

I had a quick look through your previous posts, Peego, I couldn't see any mention that you are lampworking - Glyn is talking about using a torch (the flame variety, not battery  )

[Peego]

That makes sense!