Nikopolis,
What exactly did the lemon juice remove?
What the image shows is a bronze coin with a lot of
silvering let on it. I can't tell how much of the dark is where
silvering has worn off or where there is a dark layer over the
silvering. While it is true that
patina is
good and is usually to be kept with
silvered coins it can be desireable to get green or black stuff (technically
patina) off the
silvering.
In any event it is very risky to use lemon juice on a bronze coin though some people do to tackle to stuff on the
silvering. Make sure you have soaked it in distilled water with several water changes to neutralize the acid. Even dry it can
still be attacking the coin.
They the only way to tackle to coin is mechanical.
Sharp blade and magnification.
Shawn