Chris's Metal Detecting Page -
Soaking in Olive Oil or WD40
njminerals.org is mainly about [what else?] mineral collecting,
but Treasure Hunting is somewhat related.
There is
something about finding things that has an almost universal
appeal. This is especially so for people who already collect
stuff! A mineral collector, for example, can easily cross over
into gold prospecting, metal detecting, relic hunting, and other
hobbies. If you're a metal detectorist out there who's never
gotten into mineral hunting, you might want to try it sometime!
Cleaning Dug Coins
with Oil Soaking
Anyway, let's get on to the story.
A White's Eagle II SL had been sitting in a closet for a few years, untouched. At first the thing wouldn't even detect a dime or penny on DISC mode, which was weird. There was something wrong with it. I took it apart, blew off any dust inside & dumped out any grit that found its way into the case, made sure nothing was shorted out, and put it back together. For some reason that did the trick-- it worked just fine from that point.
I carted the detector to a thoroughly-pounded area where I'd never found anything good. That sounds really encouraging, doesn't it? Well, this time I just felt lucky. After digging up a couple of crumpled soda cans, 3 or 4 pulltabs, and a piece of aluminum sheet, I got a pretty solid signal and dug up a penny-sized coin at maybe 3 inches depth. (I put that in my pocket-- if you can't see the details on a coin because there's too much dirt, DON'T rub it off while you're in the field. You might scratch the coin permanently.)
I went back to swinging the coil. About two feet from the first coin, I got another good signal and dug up a big coin that was too big to be a quarter. It was about 3 1/2 inches deep. It was too dirty to see what it was, so of course I kept it. Judging from the amount of corrosion, it was old.
I rinsed them off when I got back. The first one turned out to be an Indian Head penny. As of the time this article was originally written, I'd never found one of these before (believe it or not). The second coin was even better... it turned out to be an early large cent (which I'd later learn was a Liberty Cap or Draped Bust, made between 1793-1807). Even though badly corroded and probably worthless, it's still noteworthy as far as I'm concerned. What were the odds that all those people in the past had never put their coils on those two spots and dug those fairly shallow coins? I guess it was in the cards to find them and write this little article. The discovery of those coins, in fact, was what prompted the graduation to a newer (2000's) metal detector. If there were still a couple coins at only 3 or 4 inches depth, what was there at deeper levels? Only time would tell.
I could not read the Large Cent's date, but at least I could narrow it to a range based on the design on the coin's reverse.
The large cent
had dirt stuck to the front. I didn't want to rub it off and risk
scratching the face badly. I decided not to do
electrolysis; this time it seemed better to have thick green
patina than freshly-cleaned pitting. So here begins an experiment
with oil soaking. A prolonged soak in oil is considered the only
widely-acceptable coin cleaning method, besides
soaking in water. There are some minor qualifications, of
course (Read my article on the chemistry
of cleaning
to find out more.) Olive oil, WD-40, and Liquid Wrench are
popular types for this procedure. If you want the most chemically
inert oil for soaking, then mineral oil (U.S.P.) is probably the best
choice.
Above: Both coins, Reverse, prior to oil soaking. At least the backs were vaguely readable. Even a badly worn-out or corroded Large Cent isn't something I'd subject to electrolysis, unless it's so bad that no details are legible in its current condition. (The 1921 George V penny wasn't quite rare enough in my estimation to escape electrolysis)
Below: Both coins, Obverse, prior to oil soaking. Look how much dirt is stuck to the front of the Large Cent, even after rinsing with water. I used a hose nozzle with a jet, too. I didn't want to rub the coins with my fingers for fear of obliterating what little detail might remain. As you can see in the photographs, copper doesn't age well in the damp, highly-mineralized soil of the Eastern states.
The Indian Head cent has a
semi-legible date that says 1870-something. I don't think that
last digit is a 7, but it would be nice Hopefully the oil soak
will bring it out a bit.
 |
Left:
the obverse of the
Large Cent
after soaking in WD 40 for 8 hours and very carefully lifting away dirt
with a sharpened
toothpick under a microscope. There is still a layer of
corrosion on the coin, but most of the soil is gone now. I
compared the coin to one in a book;
it's either a Liberty Cap or a Draped Bust cent, made between 1793 and
1807! This is my
oldest
coin find yet! The date on this specimen isn't readable.
Sometimes you just have to accept that the detail is gone; we'll
find out whether a longer soak helped this coin, if only I can find
that little beaker where I put it. |
As you can see in the photo below, the eight-hour soaking removed caked-on soil from the reverse as well. The photo looks like two dug coins lain side by side, but it's just a single one: Before and After. Sometimes dirt is the only thing that lets you see the contrast of badly-corroded or worn features.
Even though it looks as if we've lost
detail
in the large cent's reverse after soaking, at this point all that's
really been done has been to remove stuck-on surface dirt. There
has been no abrasion or
chemical etching of the actual coin surface thus far.
The Bust cent and the Indian
Head cent are now both soaking in olive
oil (separate containers). I may leave them for at least a few
months before I try anything more on them. I have noticed
that, underneath the brown corrosion on the Indian Head cent, there
lies a layer of green corrosion that is starting to show. This
green layer is very thin and might qualify as "patina", if only I could
expose the whole thing. Two or
three small flakes of brown corrosion have lifted to reveal the green.
Sometimes the corrosion goes so deep on a copper coin that the detail
is actually made of
corrosion.
UPDATE: These projects were
put aside for a while. The oil-immersed coins were still sitting
around in tiny beakers (or possibly plastic cups... can't remember),
last anybody saw them. When they turn up, we'll take a look at what
happened after a couple years in oil.
The most important thing to remember is patience;
oil soaking can take a year or more. The subsequent de-greasing
can take many changes of acetone, each lasting at least several days.
If the coins for some reason never
do turn up again-- how silly, to find them with a metal detector and
then lose them again!-- at least consider this. You're not going to
turn a badly-worn or badly-corroded coin into something it can't
be. If the metal is gone, don't expect to bring out much with an
oil soak. The reasoning behind the procedure is simply to loosen dirt.
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