Copper Backings

“Is it possible to to fuse copper to the back of glass?

The easy answer is - no.

But it can be done. There are a number of conditions that will help.

The copper needs to be thin and flat. It works best if you clean the copper of any oxidisation, 
and then coat it with borax or other devitrification spray that can act as a glass flux.

The fusing has to be done with a long soak to ensure the bottom of the glass is as soft as the top to assist the attachment of the copper. The devitrification solution will help soften the glass next to the copper sheet. You also have to protect your shelf from contamination by the copper sheet. This can be done by using 3mm fibre paper under the copper.

Not all attempts will be successful, showing that this process is on the edge of acceptability.

It is easier simply to glue the copper to the back.

“Does it matter whether it has been fused already?”

The glass does not have to be fused prior to attempting to attach the copper to the back. If it has been fused, you need to run a slower schedule than when fusing glass for the first time. A schedule for slumping, but with a higher target temperature – at least fire polishing – will be required.