Cleaning coins that have been sitting in the ground for around 2000 years is no easy task. It is really easy to completely ruin these coins by overcleaning them. Especially bronze coins can be very tricky. For Roman coins to have any financial value for collectors, they need to be readable and have a solid patina. In this guide I will try to guide you through the process as well as I can.
I recently purchased a lot of around 60 uncleaned Romans. The seller was so kind to include a very beautifully cleaned coin of Arcadius to my order. Usually when you order uncleaned Roman coins, they have already been sorted by the seller to pick out any valuable ones, and you end up with mostly poor quality 4th century coins. Here, this was obviously not the case as I have already found a few exciting coins in the bunch. What do you need to watch out for when you want to buy uncleaned Roman coins?
If you find an advertisement on a platform like eBay, make sure that the advertisement shows each and every coin that you will receive. Often sellers will post an advertisement saying ”random lot of 20 uncleaned Roman coins”, accompanied by a picture of hundreds of dirty bronze coins. This way you will not know exactly which coins you will receive and it becomes very easy for the sellers to “scam” you. Do not buy from these sellers as they will have thoroughly searched through their lots to make sure they give you as less value for your money as possible. Also, do not buy from sellers who sell on a “pay per coin” basis. They have the same strategy which will make you end up paying even more for even less. My tip would be to buy from individuals (such as metal detectorists) who do not have the time/interest/patience to clean all their coins rather than businesses or sellers with loads of advertisements. Generally, do not pay more than €1 - €1.50 per coin unless you can see that the coins are of very high quality.
Now that you know what to watch out for, let’s go back to the lot I bought. In the picture below you can see how they looked when I got my hands on them. Quickly after receiving them I discovered that there was a dirty contemporary forgery in the lot. These are ancient forgeries which consist of a bronze coin with a thick silver coating, appearing to be a denarius. Unfortunately, the one in my lot is unidentifiable. I will exclude it in the rest of this guide, since silver coins require a different (and much easier) approach.
After quickly inspecting the coins when they just arrived, I started the cleaning process. The first thing I do is something not many people do. Often, you start with placing the coins in distilled water overnight and inspect them again after it. Instead, I directly start with a method I call “the frying pan”. I place the coins in a pan and cover them in olive oil. Then, I add a bit of distilled water and a few drops of lemon juice. Once the oil is boiling, I leave it like that for around 30 minutes. Make sure to stir regularly, as you don’t want the coins to stick to the bottom of your pan. After 30 minutes, turn off the stove and let the oil cool down. Once it has cooled down, use a colander to separate the coins from the oil and rinse the coins in the sink. Dry them off using an old towel and separate the readable coins from the rest. The readable ones are now finished and can be identified. Put the rest of the coins in a bowl with distilled water and leave them like this for a few days.
After a few days, remove the coins from the distilled water and create a setup like the one in the picture below. Now, brush and dry every coin separately on the towel. You can use skewers like these to remove the dirt from the coins. This is especially useful for areas between the letters and around the portrait. After removing the dirt, brush the coins again and once you are finished with all of them, rinse them with water to remove any traces of dirt left. Now, dry them and separate the readable ones from the rest again. Instead of using distilled water, this time use olive oil to soak the coins in. Let them soak for 1-4 weeks and repeat the same process until each coin is identified or until you feel like the coins which are left will not improve any further. For the best results, switch between distilled water and olive oil every time you have cleaned them.