/diy/ - Do It Yourself

>>1705359
>piece of rock
Acetone or ethanol work well as solvents.

https://yarchive.net/metal/soldering_flux.html -- about acid, read the whole text
Short excerpt for the fluxophiles:
"If you need some extra rosin flux, go to a music store and buy a block of rosin like those used by violin players. Ask for the oldest, dried-out block which should make the store owner happy (the musicians prefer the soft, sticky ones). Dissolve as much of this as you can in a small glass bottle containing acetone. Remember acetone is VERY flammable. But it evaporates quickly leaving the rosin behind, ready for soldering. One block will normally last a lifetime."