Agree on copper, bronze, and such. Easy as PIE.
Key to success: BRIGHT shiny by scrubbing with emery paper or like, dermel have a fluff ball of this soft material useful for speedy preparation or acid etched if too oxidized and in hard to access and NO grease, water and any residues this means washing, or degreasing. That means very clean.
Flux flux and flux. Use rosin flux paste & brush. Not acid-based type. This will be messy, but no big deal on clean up after.
Thou Shalt NOT overheat, ever. This oops "burns off" flux prematurely and rendering the preparation effort wasted and start over again. Heat carefully and control the heat by withdrawing or "fan" the work with tip of flame back and forth if it get hotter too quickly and solder not spreading in well or "tacky" (not enough flux or heated object not hot enough while you are "burning" other spot by accident. Keep waving the flames over larger area to get larger area come up to solder melting point while you are tapping the spot with solder wire till it suckles on the solder into joint, then move on to another spot till job is complete in one go. Wait for it to cool. Don't fuss with the repair, let solder solidify.
I've been doing the electronic solderings and some big soldering jobs for most of my life.
Cheers, Wizard