Hello Heather, It sounds like you do not have enough heat to get the
copper up to temp. Copper melts at a much higher temperature than
sterling, so don’t worry about melting the copper! However, your
little butane torch may not be capable of generating enough heat -
especially if the copper piece is very large.
When I solder copper using sterling solder, I use Battern’s flux
generously, place (or use the pick) the solder, then really turn up
the flame and get the copper red hot. Flow happens.
Hope this helps,
Judy in Kansas, where it was a breezy warm day - finally started
cleaning up the flower beds.