The question arises if you'll ruin the insulative integrity of that cup, as the insulation may not take even a lot more than it was designed for. I'd not want to run that risk, but I don't know if...Ron Spokovich 02-24-2017, 03:29 AM
First off, were the two metals (the overlay being tinned first) clean and fluxed well?
You could also try black flux the next time. Get it from a welders supply...
Looks like copper plate from here... with a very thin plating over it that wore through just from the friction of your hands?