huge bubbles..

[sandmor1]

Hi, I sprinkled an 18cm x 12cm piece of transparent aqua blue glass (3mm) with course frit and capped it with Tekta before fusing at my normal schedule for 2 layer.

I was surprised when it came out with about 5 huge bubbles and another 5 slightly smaller ones.

Could someone confirm that the course frit was probably the reason for these bubbles as the schedule I used works really well in my kiln.

Should I have fused the course frit with just the bottom layer.

Thanks

Sandra

[flame n fuse]

I think it's probably the frit - to leave an exit route for the trapped air, you can try putting a few transparent, or base layer coloured stringers between the frit and the edge of the piece

[micpru]

I would put the grit on top of the 2 layers of glass which my help avoid the bubbles. x

[sandmor1]

 I thought it was probably the frit as everything else was the same.

....but I have also just thought of something else...I had cut the cap a fraction larger than the bottom layer, as I usually do.  So now I guess that was also the wrong thing to do when using course frit.

I will try again with both your ideas and see what works best for me but also keeping the cap layer to the same size as the 1st .

Many thanks

Sandra

[MeadMoon]

You could try tack fusing the frit onto the base layer and then adding a layer of clear powder frit to even up the lumps and bumps before adding the top layer and full firing.  Also look at Bullseye Tech note 5 on reducing bubbles & distortion: http://www.bullseyeglass.com/images/stories/bullseye/PDF/TechNotes/technotes_05.pdf

Stringers of the same colour or small pieces of frit in the corners can help the top layer from sealing at the edges before the middle, but can also leave visible marks and you are still likely to get bubbles around the pieces of coarse frit.

Here's another of the Bullseye info sheets on using powder to minimise bubbles: http://www.bullseyeglass.com/methods-ideas/powder-power.html