Cleaning my first ancient coin: surfaces question

I am cleaning my very first ancient coin. I purposely chose one that does not seem to have any real design features on it at all, so that if I mess it up, it won't matter.

I soaked it for about 20 minutes in a bit of water with dishsoap, and scrubbed it with an unused toothbrush also. The coin is dry, and looks much darker than it did in its raw, uncleaned state.

What I need to do now is to understand the surfaces of this coin. There are darker brown parts, which seem to be a series of layers on the coin, and lighter greyish light brownish parts at about 11 o'clock, 1 o'clock, and in the center, which are buried underneath those layers.

I am wondering: are the dark layers I'm looking at the patina, or are they just crud to be removed?

Next time, I'll probably try using olive oil rather than dish soap. If anyone has any favourite tips regarding methods that work for them, I'm all ears. I've got 12 left to play with!

If the coin in question is too far gone for anyone to answer, please let me know.

My thanks to anyone who can help me out!

 

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Two important skills in cleaning coins are selecting 'battles' that you can win and knowing when to stop. Dirt washes off but surfaces corroded and already eroded below the original surface level do not. You might clean this one down to metal but you will not have a nice coin. We see here many coins shown as cleaning successes that are horrible looking. You can remove things from the surfaces of a coin but, when the surfaces have been removed, they are gone forever.

For the record, I have never seen a coin cleaned in olive oil that I really liked. Exhaust all other water based ideas first. A dealer once showed me a coin of Uranius Antoninus he was carrying in his pocket along with his modern 'spending' change. His idea was, slowly, to wear it down to a smooth 'fine' from the rough 'very fine' it was then. Today, many people accept poor surfaces better than we did then.

 

Whether to call the surface "patina" or "encrustation" is kind of a moot point with this coin. It looks like there is something corroding the coin's surface under the patina.

Have you ever tried using electrolysis to clean a coin? This would be excellent coin to practice on. Remove everything and take the coin all the way down to bare metal. I doubt you will see much more recognizable detail once you do this, but at least you will arrest the coin's slow self destruction.

There's a good chance that if you do expose the bare metal surface, your coin will develop the dreaded bronze disease (BD). This should not deter you. It is unlikely that your coin will prove to be anything special, and BD moves pretty slowly. If it does occur, it will provide you an opportunity to learn how to treat coins with it--a valuable skill if you see it happening to nicer coins. BD, though nasty, is easily treatable, and many people here are happy to talk you through the process should the need arise.

 

That coin looks like a Byzantine billon trachy. These coins are very thin, as you can see, and this coin is very heavily encrusted and corroded. I don't think any removal would be beneficial.

Perhaps you could locate an ancient that doesn't have these significant surface issues for cleaning?

 

I feel like, there's really no way to make this coin worse than it is.

Great guinea pig for different treatments to see how they respond.

I would go with sodium hydroxide to remove surface minerals, and see what you're looking at from there.
Often times, a few hours in NaOH will allow you to mechanically clean the rest of it, with minimal damage to the coin fabric and minimal risk of going down to bare metal.

 

Nathan, do you have a photo of the other side? Often, with this type, the concave side has pretty good detail. The convex side is very often quite bad, due to weak strike, off center strike or just plain wear.

 

Thank you, Doug! I agree with you very much that this particular coin is a lost cause, but I still want to use it to understand the process of cleaning coins, and also the nature of ancient coins surfaces. Regarding your olive oil comment: noted! The dealer I bought them off of said olive oil worked best. At the moment, I've got one in olive oil; plus the one pictured above; and one that I've been soaking in distilled water and going at with a toothpick and occasionally an unused toothbrush. So far, I think I've killed that one! That gives me ten coins left that are still untouched.

 

Thank you, gsimonel! Regarding electrolysis, I am very interested, but I don't have any equipment to do it. I actually don't even know what that equipment would be. I do remember an ultrasonic cleaner from when I worked in a coin shop (it was actually used almost exclusively for jewellery cleaning, though), but I doubt there'd be any money in the budget for that...

 

Thank you, hotwheelsearl! I agree that there's no way to make this particular one worse than it is. So it's an experimental piece. I've never used sodium hydroxide before, and barely know what it is. I should look into that by the sound of things.

 

Good heavens, man! How can you get anything at all out of that photo? I don't know how you do it! As for the other side, here it is in all its glory! ;-)

 

Typically sold as drain cleaner in many hardware stores. It’s a very strong base and can cause chemical burns, so use with caution.

in my travels if cleaning, it’s often a first resort to get minerals down enough to see a general form; from there I determine whether to attempt mechanical or pursue more mild chemicals.

 

Actually, you do. You just don't realize it.

Here's one way to use Electrolysis. The only thing they got wrong is that if you use salt or lemon juice as a solute, you should stir in a little bit of baking soda every now and then to reduce the acidity of the solution. (As the salt breaks down, it turns the water acidic.) Or you could just use sodium carbonate as your solute, like I do. You can find it in in the laundry detergent section of your local grocery store under the name of Arm & Hammer Washing Soda.

Here's another version that uses 4 AA Batteries instead of the AC to DC converter.

If you don't have alligator clips, just wrap the wire around the coin or make a basket with paper clips. Experiment and have some fun, but to start out, use only hopeless coins.

 

Thank you, gsimonel! I'm going to try this.

 

Electrolysis may not give you the results you desire.

I bought a large lot of 97 coins from Roma, no less. All were heavily electrolyzed to bare metal. In an attempt to re patinate they were doused with some sort of motor oil.

Even after cleaning, they were pitted, rough, and generally awful.

electro is a last resort. I would 100% recommend going chemical first

 

I must say, I find coin cleaning extremely frustrating so far. I'm glad I'm doing it because I think it will help me to understand the coins, but I am glad I bought a small lot of only 10 coins (with three "free" coins added) instead of a large lot. I don't really know what to do.

Here's another coin I tried cleaning. First I used some water and a bit of dish soap, and I washed it. Then I rinsed it. Then I had it in distilled water for 30 minutes or so, then I scraped crud off it with the but end of a fairly thick toothpick as well as my fingernail and an unused toothbrush. I repeated these steps for about a day or so. In the beginning, this coin was greyish. Then it got kind of dark greenish. Then it got to its present colour, which is a redish-brownish colour. On the obverse, I can see the diademed head of a man facing right. If he had a massive mustache, it would be where a lot of crud is. There's also crud behind the back of his head, and in other places.

For the reverse, I can't make out anything at all except a tiny ring-like shape. I can see that there were legends, but I can't read any of the letters. Would anyone have any ideas what it is (if you can even see anything at all out of these photos)?



I feel like I scraped off too much from this coin, although it seems to me that it is corroded anyway. I should have photographed it before I began, but I forgot. Next time, I'll take a picture before doing anything at all.

 

That’s why I like sodium hydroxide. It sloughs off most of the minerals with minimal impact on the coin itself.

mechanical scraping often is a tough mistress.

 

Thank you! I think I will have to buy myself a bottle of this. Can I ask how long you leave a coin in the sodium hydroxide before you pull it out to have your first look at it? How long would you leave an average coin in there?

Also, I have another question: can sodium hydroxide harm a coin (aside from being in it too long, I guess)?

 

I tend to leave coins in NaOH for 5-8 hours, basically overnight.

You can 100% leave them in for too long. Initially it tends not to impact the coin much, but after too long it can leave them pitted and rough.

It can also change the color from green to a brownish color.

Trajan Decius. It was encrusted, and artificially run through a rock tumbler. It was initially green.

I left this in NaOH for about 8 hours, and ended up with this:

The color changed significantly, but it removed nearly all of the encrustations without any major impact on the surfaces of the actual coin.


The main problem is if the coin has an original greenish patina, it will 100% be removed.

This had a nice dark green patina, but the encrustation would never have been removable mechanically.

This took about 12 hours in NaOH. The color became brown, and the surfaces got a bit rough.

Something to note, however: if a surface becomes rough after chemical treatment, it usually means that the encrustation or corrosion had already impacted the surface. Basically, nothing could have been done to prevent surface roughness on some of these coins.


Sometimes, the host coin is just too far gone and there's nothing to be done.

This Trajan had a host of minerals. The minerals were rough, there was no patina to speak of.


Cleaning involved NaOH, sodium thiosulfate, and acetic acid. The chemicals cleaned off the minerals, revealing the originally poor surface. However, in this case it restored the original yellow orichalcum color.



Basically, NaOH is my best friend. You may sacrifice some patina, but you can make up for it in overall details.



Here;s an example of purely mechanical cleaning.

The encrustations appeared to be rather fragile, so I opted for a mechanical attack with distilled water soaks.



I saw a lovely green patina underneath, which is why I didn't subject it to chemicals.
However, the surfaces are kinda rough despite my best efforts. At this point its a judgment call whether to lose the green patina in favor of brown, or to live with a very rough surface.

 

An ultrasonic cleaner will remove any lose deposits, but so often will a good soak in distilled water and a gentle brushing.

Olive oil is mildly acidic, so it will dissolve the surface of the coin and maybe some of what is on it. Because it is such a weak acid, coins can often be left in olive oil for weeks on end with only minimal changes. Because there can be a range of PH and additives, I agree with Doug and refrain from using it. Many deposits are stable and will not be affected by acids.

Alkalis often work on things acids don’t. Bronze disease, for example. Many deposits are stable and will not be affected by alkalis, either.

Organic solvents can work, but the heavier ones are strongly carcinogenic so you need to decide how badly you want to clean the coin. MEK is nasty stuff.

Electrolysis is entertaining. Wrap a silver coin loosely in aluminum foil and drop it in a basic solution (sodium hydroxide or baking soda) and the tarnish (patina) is reconverted to silver. A rusted piece of iron is even more exciting as it fizzes away, converting the rust back into iron.

Sometimes the only way to make progress is mechanically. A microscope and appropriate picks can do wonders in the right (read: not my) hands.

Here are a few things I’ve learned from messing around trying to save coins:

1) If it improves at all consider it a win. Stop.

2) Don’t expect miracles. Remember what you started with

3) Know when to stop. I’ve worsened more coins trying to make them a little bit better.

4) Virtually every coin you buy from a reputable dealer has been prepped by someone who knows more than we do on the subject. A good rule of thumb is to leave those alone.

5) Uncleaned coins are sold uncleaned for a reason.

Most of all, have fun.

 

Thank you for those insights. I have two very basic follow-up question for you.

First, when you refer to "sodium hydroxide" is that something that is pure? I went to my local hardware store, and the closest I could come was a bottle of drain cleaner crystals ("Drano" brand). The label says "contains sodium hydroxide," which to me implies that this is not pure sodium hydroxide. Can you tell me if you think this will work?

My second question is, how do you put the coin into the sodium hydroxide? Do you mix the crystals with water (assuming that won't blow something up!) or do you just put the coin straight into the crystals?

At this point, I have got a few coins on the go, all looking quite terrible!

Coin #1 I put in olive oil as per the dealer's recommendation before coming to this thread. I don't have a photo of that here.

Coin #2, which is the coin in the original pictures, looks like a metallic piece of, well, I'm not supposed to finish that sentence. I tried electrolysis on it as per gsimonel's recommendation. I had too much trouble stripping the very fine positive and negative wires, so my brother did something for me.

I think this coin may be too far gone even for electrolysis. It's very small and black now, and has lost a lot of its mass (guck, or guck and surface?--I don't know). I'm going to keep trying because I don't think any design elements are visible yet. In any case, electrolysis is fun! I like the sizzle and the way the water changes to thick black stuff! If it ever gets better, I'll post a pic here of each side. And if it doesn't, no harm done; the coins were cheap and this one is a lost cause, I believe.

Coin #3 is the second coin shown above. I'm not really sure what to do now that I've got it to the state it's in. Perhaps I've done too much and there's nothing further to do. Or maybe I need to give it more time in the water.

Coin #4, I haven't shown yet, but once I figure out this sodium hydroxide stuff, then I will try that on it.

After that, I will still have nine coins left, but it seems to me that they are all extremely low grade and probably won't really turn out well in any case.