I recently got this
Magnentius which while not an uncleaned coin, needed some fixing up. The "
patina" was a mixture of ancient grease, dirt, and tarnish which, while soft, is impossible to remove manually without
scratching up the coin - it is like a slippery ugly black varnish. I forgot to photo the coin before I began but the seller photo's show the look of the coin before cleaning. The
obverse is particularly bad because it is lightly struck.
After some
scratching at it with hard
tools I decided to let it soak in some WD-40 oil for a few hours and then
work at it with a cotton Q-tip. The combination of light scraping, soaking in oil and rubbing with
fabric basically removed this sludgey coating. Since WD-40 is volatile (and not
cheap) I sprayed just enough to cover the coin in a porcelain screw-cap container.
The final result is shown. The little brownish spots are what is left of the coating. My guess is that this stuff is ancient in origin -possibly the remains of grease that was put on the coin to
help preserve it when it was put in the ground. The oil-base makes WD-40 reasonably effective at removing it without a lot of
work.
There is of course some sacrifice when this stuff is removed but fortunately the metal underneath is in pretty
good condition and the coin, in hand, is much more presentable.
Regards, Dave