Copper foil piece gone horribly wrong

[Abundantglass]

I have been commissioned to create a large piece (600 x250mm) using bullseye glass and small copper foil hearts. I have fired the foil between two layers of clear (tekta) glass on a full fuse. The results are perfectly fired red hearts around the edges, then a circle of hearts with bubbles on each piece and then in the middle a large black area - it looks like each of the hearts has burnt and sent smoke in the surrounding area. No bubble in this section. I am assuming I need a longer bubble squeeze but I could do with some advice on what might have caused the black area and how I can avoid it. The same foil was used throughout and sourced from a glass supplier.

Thanks

Jane

[Brad Walker]

Do you have a photo and a firing schedule?

My guess is that it has to do with the amount of air and heat getting to the middle of the piece versus the edges, but a photo and schedule would help.

[Abundantglass]

Photo attached.

Firing schedule in centegrade:

222 to 677 hold 30 min
333 to 795 hold 5 min
999 to 482 hold 60 min
83 to 371 End

Thank you.

Jane

[Morganica]

How are you cleaning/applying the hearts?

[Marty]

After Cynthia gets done with the hearts and you try again, slow down on the way up and hold at 600C, not 677.
If you find you're still trapping bubbles, use chads to have the middle sag first.

[Bert Weiss]

It looks like you used an organic adhesive. As the glass sealed around the unburned leftover adhesive, it left the unburned organic matter in there. What little oxygen was left, combines with the burning carbon and can stretch the glass out when it is hot enough to move around.

On the order of the chad idea, you could try the opposite, and make the hearts thicker in the center so the glass sits on them, and drapes around them, or the opposite and make the hearts thicker at the corners so the center slumps first.

I would also put in a long hold around 1000 to completely burn any organics out before the glass moves around.

[Brock]

On the order of the chad idea, you could try the opposite, and make the hearts thicker in the center so the glass sits on them, and drapes around them, or the opposite and make the hearts thicker at the corners so the center slumps first.

Great idea! If you like heart shaped bubbles . . .

[Abundantglass]

I'm embarassed to admit that it has never occured to me to clean the copperfoil. It comes with adhesive on one side. I've made many smaller pieces and never once had problems with it. Would you recommend different foil and a different adhesive?

Thanks

Jane

[Brock]

Use copper with NO adhesive.

[Hedda]

I found that a very easy way to clean the adhesive out of the copper foil is to boil the foil with some baking soda [sodium bicarbonate]. After several minutes I spool the adhesive on a wood skewer.

[Mark Kemp]

Yeah, I've used the adhesive copper foil in small things and it works, because the adhesive is able to burn out before the glass fuses. But I can see why it wouldn't in something larger.

[Marty]

Yeah, I've used the adhesive copper foil in small things and it works, because the adhesive is able to burn out before the glass fuses. But I can see why it wouldn't in something larger.

Because the glass is slumping and sealing around the copper so the adhesive burn-out products have no where to go but up. Hence bubbles.

[Abundantglass]

Some what belatedly.... Thanks everyone for the advice. Refired with clean non adhesive copper foil. Added a few bits of frit at the edge as chads and tried the recommended schedule. Result was perfect. One happy customer.