Chris's Metal Detecting Page -
Electrolysis of Dug Coins
Chris's Mineral
Collecting Page is mainly about [what else?] mineral collecting,
but I
thought I'd put a little bit of Treasure Hunting stuff up here as
well... I may start enlarging this little sub-section if time
allows. Behold, Chris's Metal
Detecting Page.
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.
Over the years
I've done a little metal detecting, at least when I'm not searching
for rocks and minerals.
Coin digging
Twenty years
ago, those metal
detector brochures used to show the people with a blanket laid out
in front of them where they've spread out like 80 zillion silver
coins. Or you see the photo of some guy who found a gold
sovereign the first time out, under some kid's swing set in a park that
he somehow luckily guessed was 100 years older than everyone thought
possible. Well, in all my years of detecting I
found mostly clad (modern)
coins and a lot of junk. Pulltabs, foil, nails, and bottle
caps... I
am the
king of rusted bottlecaps. I've found absolutely no
gold coins and very little silver. As of the time of writing
this article, I've ever found maybe 5 silver
coins (junk silver, common dates), a couple Buffalo Nickels, and a
badly corroded 1858 Flying Eagle
Cent where you could barely, and I mean barely, read the date after
squinting at it really hard. I
was pretty psyched about that find, though.
The fact that I
never found a whole lot of great stuff was probably due to (1) my going
to sites that
had been pounded thoroughly by other detectors, and (2) my lack of
patience when I didn't find the 80 zillion
silver coins I saw in the brochures. I did find a single jack,
though: the toy kind that you pick up when you bounce a
ball. It was rusted to pieces and all by itself, missing the rest
of
the jacks.
It lay buried almost a foot deep at an old house site. Have
you
ever played jacks? This one wasn't much good for that. It
crumbled into dirty red flakes in the box where I stored it.
(Somewhere on my to-do list is to write an article on preserving iron
relics).
Anyhow, digging
up coins brings us to an important debate that still rages on the
forums: Should you clean your coins?
The answer is, you should not
clean a coin if it's one of the
valuable dates or otherwise rare. In that case, the most radical
thing you
should do is soaking in distilled water or maybe an extended soak in
oil (which can take a long time). Many beginners to the hobby
have ruined a lot of good coins by taking metal polish, buffing wheels,
or steel wool to
them. The scratches these cause will ALWAYS show up with
magnification, and
an experienced collector will often be able to spot such harsh
treatments at a glance. Buffing, polishing,
or abrading cuts the value in
half, sometimes worse. An honest dealer will always disclose this
kind of treatment.
Same thing with acids- vinegar, muriatic,
you name it- they are destructive treatments and should be disclosed if
for some reason they've been used on a coin. They dissolve some
of the metal and take away fine
detail. Lye will also attack most metals, though in another
article I'll explore the limited uses of lye solution for cleaning
coins.
Some of the
coins you dig up are either so badly corroded or are of such
common date that they aren't worth much in the first place... so what
about them? I
doubt anyone would care if you overcleaned a common-date Wheat Cent.
I'm not saying to turn your dug coin into a shiny disc,
however. Sometimes dug coins have character that goes beyond
value, even if the coin "books" for only 25 cents. In a few cases
it might be nicer to see a shiny, valueless coin
than a dirty, valueless disc with no visible detail, but if you can
read the date and the coin has a nice patina, leave it alone. If it's in
such
bad shape that you feel you must clean it, just make
sure it's really
something common or of low value before you work on it! Most
clad coins are only worth
face value, so you can go ahead and scrub 'em till your heart is
content. Just watch you aren't ruining any Doubled Die coins or
anything like that.
One more
thing: If a coin is really dark or pitted BUT it's a rare date,
don't clean it yourself. Have a numismatic conservator look at
it. If it is something really valuable it would be worth the
money to pay a professional to work on it, or else just leave it alone
completely. A few coin dealers are
a
little sketchy and might tell you to clean a valuable coin with Tarn-X
or Nevr-Dull or something like that. DON'T do this to a coin
unless it's already of little value the way it is.
One method of
cleaning your dug coins and relics is electrolysis.
This works very well for iron relics, which are often extremely
rusted to the point they are unrecognizable...
a couple guys cleaned
up some civil war relics which, if I had the money and collected
Civil War relics, I'd definitely love to buy the cleaned ones.
The as-found state was so ugly I doubt even the most obsessive purist
would want them. (A rusted blob where you can't even discern the
shape of the object is not very appealing.)Anyway, you use
a car battery charger as
the power source and sodium
carbonate or sodium bicarbonate solution as the electrolyte (WARNING: it is YOUR
responsibility to do it right. I don't want to hear about
it if
you hurt yourself or cause a fire.) If you hook up
the electrodes backwards you will cause the coin to be eaten
away. Remember, Oxidation occurs at the Anode. Hooking a
metal coin to the Anode will cause the metal to dissolve into solution,
effectively
turning pure metal into ions floating around in the liquid (this is
called "reverse electrolysis" and is used only when it's desirable to
dissolve away some of the actual metal).If you hook up
the electrodes properly but have dissolved metals in the solution,
they
could plate out on your coin and ruin it, too! Stainless steel
anodes will put iron and chromium ions into solution, but normally
there has to be very high current to get chromium to plate out on
something and stay there. As for iron, I have to check the table
of standard reduction potentials- I can't remember offhand if it will
plate out. Certain other metals, such as nickel and zinc, will
almost definitely plate out on the coin. You will
probably never get it off of there once it plates out on the
coin. Copper salts are the
worst in this respect-- never use a copper wire as the anode.
Contrary to popular belief, you can use a copper wire at the
cathode. The copper will not go into solution when it's the
cathode. If the you find
the previous paragraph confusing, just make sure to use a piece of
carbon or graphite for the anode. Then you won't have to worry
about the whole issue.You want the
coin hooked up to the NEGATIVE terminal (the cathode). Just
remember: Coin,
Cathode.
The cathode is the negative one (if you don't know the difference
between anode and cathode, just think of "Black Cat", because the
negative terminal of a battery charger should be the Black one. The
black cat gets the coin). The positive
terminal (the anode) should be hooked to a CARBON or
GRAPHITE rod. A "pencil lead" will work OK; these are
carbon, not real lead. You can cut open a wooden pencil very
carefully down the middle, but you will probably break the graphite in
the process. Even a correctly-done setup may appear to cause some pitting of the coin. Actually, what happens is that the corrosion or tarnish has already eaten into the surface of the coin long before you even dug it up, and now that you're removing this corrosionlayer, you will see the metal pitting left behind. Oxygen bubbles form at the cathode, and these bubbles will cause some of the corrosion or tarnish to flake away from the coin. That's OK. You are not actually dissolving the metal when the coin is at the cathode. If the coin is pitted after you did proper electrolysis, that means the tarnish had already eaten into the surface.
I found a 1921 George V penny (British) at a friend's house in New Jersey, maybe 15 years ago. It was buried about 11 or 12 inches deep, no exaggeration (I had just gotten a White's Eagle II SL, which in the opinion of some enthusiasts is still one of the best detectors ever made... though I was surely no expert with it!) So anyway, this penny was very tarnished. Thick, dark green tarnish coated it to the point where you couldn't see much detail. Dirt was so stuck so far into it that soaking did not take it out.
A few days ago I
decided to clean it via electrolysis. Should I have left it
alone? Probably. The date was readable. I decided to
go ahead and use this coin in our experiment.
| Right: My preliminary
electrolysis
setup. Anode (+): hooked to a carbon or graphite
electrode. This is the only material you should use, because
metals such as steel or copper will go into solution and deposit out on
your coins. The graphite electrode must NOT touch the coin or the aluminum foil. Cathode (-): hooked to the item to be cleaned. For a coin I used aluminum foil, but I found later it's best to minimize the surface area of aluminum exposed to the liquid, otherwise the coin won't be cleaned up as much. For best results, use an insulated wire with as little exposed metal as needed to make contact with the coin. |
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| Above (Left):
Before electrolysis. Even soaking didn't take away the
dirt, but then again it was only for a few days. The 1921 George
V penny will fetch no more than about $5 if
the hair detail is gone and King George's head looks like one big, bald
cranium. Some collectors really like the green tones, even if they're thick like this. That's why you shouldn't mess with the rare ones; leave them as-found or soak in olive oil for a few weeks or months. In this case I figured I'd never sell the coin, it wasn't worth much, and... it was unlucky enough to "volunteer" for my experiment. If you are lucky enough to dig something rare, I'd advise against electrolysis until you get a professional opinion. |
Above
(Right): After electrolysis. The coin had a very
dull appearance when it came out of the bath. I dried it off and
rubbed it in olive oil for a
while between my cleaned fingers (being careful not to have any grit on
them). Then I washed off the oil with soap and water and rubbed
the coin between my cleaned, dry fingers for a while. This helped
the highlights stand out a bit, yet it
left not even a trace of scratching at 10x magnification (though there
were of course 100's of micro-pits remaining where the verdigris had
been...). Rubbing a coin with your thumb is called "thumbing" and is considered a deceptive practice when used to hide blemishes. In this case, it's assumed you're doing it to a low-value coin that you don't plan to sell, so you can "thumb" it if you want to. |
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