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What does conserved mean in this context?
Without getting too technical, it means a process of gentle cleaning that doesn't harm the underlying surfaces or patina. Start by soaking the coin in distilled water. Realize that results may may take quite some time (measured in weeks or even months) to become visible, but this slow method shouldn't harm the coin. Just don't get impatient & try to dislodge any deposits by scouring or picking at then with anything harder than a cotton swab, fingernail or soft toothpick.
In fact, before tackling this particular coin, you might be well advised to obtain some inexpensive uncleaned late Roman bronzes & practice on them. Make any mistakes on those before tackling this earlier one.
Disclaimer: This is just general guidance that incorporates established practice, & I cannot be held responsible for any damages.
Colligo ergo sum