The trick to this is to _always_ use a 'pick' that's softer than the metal/alloy of the coin.
Using something made of steel is quite a risk.
On bronze this is easy- any old bit of soft copper wire that has the end shaped will do the trick.
Re-patinating is tricky with bronze, since it's less reactive than copper- raising the temperature is the key.
Sliding the coin into a fluorescent lightbulb that's base down and on a lot keeps the coin at about 45-50ËšC,
thus speeding up patination- six months as opposed to years....
Clean the coin with alcohol first, keep fingers off it, and rotate it regularly to get the air to the surfaces evenly.
Works beautifully.