It will be great to talk about copper soldering. I make my own copper solder alloys.
Generally I use copper alloy with silver but I also made copper with zinc. I try to put a little silver to lighten not much weld and do not give much contrast.
As for% of the parts of each metal I use 80% copper to 20% silver for strong solder , and 70% copper to 30% silver for medium solder, weak solder usually 50% copper and 50% silver.
My torch is not very powerful, so. I use charcoal next to the part that will receive the solder to increase the temperature and the solder melts better.
I use the sodium tetraborate decahydrate flux.
I’m sorry, my English is not good.