A nice uncleaned lot came in today. A small lot, only 20, but some great coins in there and 11 different emperors identifiable immediately. Some only needed a little bit of work.
A desert patina is highly desirable and frames the details of a coin well so retaining it is a good idea. A lot of cleaning methods negatively affect a sand patina or will remove the whole lot indiscriminately, so cleaning has to be manual. I thought I'd do a quick write up on how I clean desert coins, as the process is somewhat different to working on normal uncleaned coins where the aim is to remove all encrustations.
I took a wooden toothpick and dipped the very tip into a pot of distilled water. Working very carefully in small circles, I slowly worked down the desert patina over the covered letters. The toothpick blunts easily; I took a knife and occasionally renewed the sharp tip. As the dirt is worked away, the coin dries and so the tip is regularly remoistened, taking care not to flood the coin unnecessarily - I only want to wet the area I'm working on.
Encrustations on the bust are harder to remove satisfactorily. It can be easy to damage the surface or remove patina by mistake while cleaning, so I usually recommend not touching it all. However, for the Theodosius pictured below I decided to do a little work on the bust. Here, the work is much more delicate and deliberate, so I didn't use water (the muddy residue can hide what you are doing) and kept the toothpick constantly sharp. Here, I wanted the sand patina to remain in the details, but be removed from the high points. I no longer work in tight circles, but instead pull the pick against the direction of the raised lines of the detail, for example, by working perpendicular to the hair. This leaves the sand patina between the hairs intact. For this work, it is easily to be overzealous but the patina can not be put back. My endpoint goal is for the coin to still appear 'uncleaned'.
I worked away around the hair to reveal the full head, removed sand that covered the end of the eyebrow to properly frame the face, and exposed the tip of the nose to define the full portrait. I also carefully exposed the full width of the diadem ties.
Here are pictures to show this work on the Theodosius. The first picture is as it was received, then with the [DO] revealed, then after the bust work, then finally after I remembered that there is a second [S] in THEODOSIVS.
(last pictures in monochrome as I could get a better closeup that way).