I have made a picture frame of square Sterling tubing and am having difficulty soldering to the copper backplate. Any suggestions would be helpful. I am first dipping all the pieces in anti-firescale mix; burning it off; fluxing; and using easy silver solder, First I tried sweat soldering the back of the frame but that didn’t work and the last thing I’ve tried is wiring frame to backplate and pick soldering but the solder will not flow.
A diagram of the piece would be helpful. Then we’d understand the size, shape, and position of the copper back plate. Also knowing the size of the frame and the tubing would be helpful.
Try medium solder…Rob
Get some powdered silver solder from Victoria Lansford. It has the flux incorporated into it. I’d still take Stainless Steel wire and bind the pieces down to the back plate after placing the solder under your tubing. Reason being the solder as it melts it mushrooms upward a bit. It can knock your tubing out of place. The wire will hold all parts in their proper place.
Can you tin the two pieces separately using the same solder but appropriate fluxes? Then you could wash the two pieces well, dry, and then bind them together. Now it won’t matter which flux you use because when you put the heat to the work you will be joining the fluxes which should be easier. When ever I have done this I have used Boric acid and alcohol through out. But I have also used Boric acid on the copper and batterns on the silver. However not in years.
Send us photos. and good luck.