Occasionally, when I have a bit of free time, I clean Roman coins. I buy a small lot of uncleaned
coins, remove the dirt and encrustations that coat their surfaces, and identify them with
the help of reference books and online resources. The process can be time-consuming, even tedious.
But at least for me, it’s rewarding in a way that simply buying ancient coins can never be.
The overwhelming majority of uncleaned coins look like the ones pictured here: small bronzes,
about the size of an American penny or dime, dating to the third and fourth centuries AD.
The cheapest uncleaned coins, sold for a dollar or two apiece, are often so worn
or damaged that they’re impossible to identify. The next step up are usually marketed as premium
uncleaned. These tend to sell anywhere from about three to six dollars per coin;
and especially at the higher end of that price range, most will clean into something presentable.
The coins in this picture, which I received from nerocoins.com, come from a good batch of premium
uncleaned. As you can see, none are broken or bent, and most have details clearly visible.
The best uncleaned coins, often marketed at about 12 or 15 dollars a coin,
are a more serious investment, but the payoff is that every coin is guaranteed to be a keeper,
and a few will be truly remarkable. These examples, also from nerocoins, are a fair sample.
No matter the caliber of the coins you’re cleaning, you’ll need a strong light source,
preferably one with a built-in magnifying glass.
You’ll also want a surface to clean on. I use a sewing mat, but a piece of cardboard works fine.
The tools are simple: wooden toothpicks, a dental pick, and a scalpel.
In this video, I’m going to talk about how to clean bronze coins. The techniques for silver
are different, but since the odds of finding a silver coin in an uncleaned lot are slim, I’ll
confine myself to bronzes here. When I clean, I try to follow a few basic practices, and the first
and foremost of these is: Be Patient. To clean a coin well, you need to work slowly and carefully.
When I get a new batch of coins, I typically wash them in soapy water, gently brushing each coin
with an old toothbrush. After rinsing the coins, I soak them in distilled water for at least a week,
changing the water daily. I use distilled water because tap water contains dissolved minerals,
and is correspondingly less effective at loosening encrusted dirt. Many hobbyists used to soak their
coins in olive oil, but that’s fallen out of favor, since oil is messy, no more effective than
distilled water, and can darken a coin’s patina. When a copper alloy like bronze or brass
is exposed to the elements, it gradually forms an oxidized coating.
This is the patina, and every uncleaned ancient coin has one. Although the color varies, bronze
coins buried in temperate climates tend to develop a greenish patina like the one pictured here.
The patina is integral to the beauty, the value, and the stability of an ancient coin.
Removing it not only strips a coin of its personality and much of its detail;
it also exposes the coin to the catastrophic chemical decay known as bronze disease.
You might encounter so-called “desert patina” coins.
Although the patina of most coins buried in dry environments is dark brown or black,
the actual surface is often covered with a thin layer of fine clay or hardened sand.
Many cleaners like to partially preserve this sort of coating to accentuate a coin’s details.
But since almost all the coins I clean come from temperate places, I usually try to remove
all the encrusted dirt. If you’re lucky, at least some of that dirt will loosen in
the initial distilled water soak. At a certain point, however, all the soft dirt will be gone,
and you’ll be left with a hard layer that doesn’t respond to soaks and scrubbing.
At that point, it’s time for the real cleaning to begin.
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To remove hard dirt and encrustations from a bronze coin, you’ll need to use tools.
In this video, I talk about the three that I use most: toothpicks, a dental pick, and a scalpel.
Other cleaners have different instruments, but most of us use the same basic technique, moving
the tips of our tools in slow, small circles to loosen dirt without scratching the patina.
I usually start with a toothpick. Although a toothpick won’t do much
against hard encrustations, it can be surprisingly effective on packed dirt,
especially when you’re trying to clear an inscription. The best thing about a toothpick
is that it almost never harms the patina, especially if you move the tip in circles.
When dirt doesn’t respond to toothpicks, I often try a dental pick,
to see whether the metal tip makes more headway. My tool of choice when cleaning coins, however,
is a scalpel with a curved blade. You have to be careful with a scalpel, both to avoid cutting
yourself – scalpels work best they’re sharpest – and to avoid damaging your coin. Here again,
whether shaving a surface with the blade or clearing an inscription with the tip,
small circles are usually the key. There are plenty of other tools,
of course; but in general, if I can’t clean a coin completely with picks and scalpels,
I just put it back in distilled water and brush it occasionally with an old toothbrush,
slowly loosening the remaining dirt. If you look online, you’ll find all sorts of
suggestions for using everything from lemon juice to copper cleaning products on ancient coins.
These can be effective if you know what you’re doing, but there’s no magic bullet,
and each method had its risks. Especially for those new to the hobby,
it’s very easy to reduce a perfectly good coin to a worthless corroded disk in a few minutes.
I never use chemicals on any decent coin, and I’d encourage you to be equally cautious.
Just to illustrate the process, I’d like to show you an example. I got this particular coin
from Noble Roman Coins. I could tell from its size and thickness that it was an early
imperial bronze, but only a small part of the reverse – shown here – was visible.
The entire obverse was covered. After soaking the coin for a week, I began
using a toothpick to remove all the loose dirt. Then I started working with a scalpel,
gently scraping at the rock-hard layer coating the coin’s surface.
Details slowly came to light. After several hours of work with the scalpel,
I managed to clear almost the entire obverse, revealing a detailed portrait
unfortunately marred by red oxidation blisters. This is the more or less finished coin.
The cleaned reverse, as you can see, is in better shape, and compromised only
by a small damaged area on the lower left. The most interesting part of cleaning a coin
is attributing it – identifying the ruler and type, and pinpointing it in the grand narrative of
classical history. For Roman imperial issues, the standard reference is David Van Meter’s Handbook
of Roman Imperial Coins, which lists all the major types. There are also excellent resources online,
including the Roman Coin Attribution Toolkit on the Forum Ancient Coins
website and the databases at wildwinds.com. To show how this works, let’s take a look
at this drawing of the coin I cleaned, kindly provided by Classical Numismatics. For a Roman
imperial coin, the attribution process starts with identifying the emperor on the obverse;
and in this case, that’s easy: Hadrianus Augustus – Hadrian. The size of the coin, and the fact that
Hadrian’s wearing a radiate crown, indicate that the coin is a dupondius, worth half a sestertius.
Now all we have to do is determine the type, and the reverse allows us to do that.
The COS III indicates that the coin was struck during or after Hadrian’s third consulship.
And the fact that the goddess is carrying a tray of fruit and ears of grain
identifies her as Fides, the personification of trust, a popular symbol of imperial benevolence.
Let’s take a look at another coin I cleaned, also from Noble Roman Coins.
This is a large bronze with a Roman emperor on the obverse. Unlike the last example, however,
this one wasn’t produced by an official imperial mint. Instead, like many coins in the eastern
Roman provinces, it was struck by a city – in this case, Colonia Viminacium, in what is now Serbia.
This drawing by Classical Numismatics makes the coin’s design clear.
On the obverse, we have the child-emperor Gordian III,
identified by the legend as Imperator Caesar Marcus Antonius Gordianus Augustus.
The reverse shows a female figure – a personification of the province – standing
between a lion and a bull, symbols of the two legions that were headquartered nearby.
This coin’s iconography reflects its purpose. The thousands of soldiers stationed around Viminacium
were paid in silver; but when they spent their pay in local stores and taverns, they received
change in bronze. By the time this coin was made, inflation was driving the bronze coins
of the Roman imperial mints out of production, making small change increasingly scarce. To keep
the local economy healthy, the city of Viminacium minted coins like this one in the emperor’s name.
Our final example dates to the era of the Tetrarchy, when the Roman coinage
was reformed and standardized. This is a follis – a large coin made with
a silver-bronze alloy – and thanks to the well-preserved inscriptions, we can
tell almost exactly when and where it was made. Moving to the drawing by Classical Numismatics,
we can see that the heavily abbreviated inscription on the obverse reads Imperator Caesar
Galerius Valerius Maximianus Pius Filius Augustus – in short, Galerius, best known today as the
Caesar of Diocletian and a brutal persecutor of the Christians. The reverse shows a nude figure,
identified by the inscription as the genius – that is, guardian spirit – of the emperor. The
letters below the figure’s feet are mint marks, indicating that the coin was produced at Heraclea,
in what is now western Turkey. This particular coin was probably struck in 308 or 309, shortly
before Galerius’ death and the wars that would make Constantine sole emperor of the Roman world.
The stories of the coins in this video began 17 or 18 centuries ago, amid the smoke and clamor of the
imperial mints. They were paid to soldiers, they were laid down in bars, they bought everything
from goats to perfume, they were surrendered to taxmen, they crossed provinces and seas. Somehow,
they were lost and buried. And ultimately, improbably, they ended up on a YouTube video.
For their assistance during the making of this video, I’d like to thank Nerocoins.com and
Noble Roman Coins. Kevin at Noble Roman Coins was especially generous with his time and expertise.
I’d also like to thank Classical Numismatics for their excellent drawings of the coins featured
in the attribution section. Thanks for watching.