Sand concretion from brass/bronze

I did this a couple days ago with a sand-concreted penny- heat with a blowtorch then drop into a jar of ice water, repeat several times.

The first run, I heated it so much it made a cracking noise and about a third of the crust came flying off. a couple more runs broke most of the rest off.

Once the surface is exposed, too much blast from the torch will corrode the surface quickly and even melt fine details, so be careful.

I wouldn't do this with a valuable find though.