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After being excavated, an ancient coin can be completely unrecognizable. It is often covered with a thick layer of organic deposits, dirt, and dense oxides that hide the relief and metal. In this condition, the artifact requires careful and systematic cleaning.
After being excavated, an ancient coin can be completely unrecognizable. It is often covered with a thick layer of organic deposits, dirt, and dense oxides that hide the relief and metal. In this condition, the artifact requires careful and systematic cleaning.
The specimen presented—a kopek from the time of Alexander I—is a prime example of such a find. Its surface is thickly caked with organic matter and has formed heavy oxides, making it impossible to see the image without special treatment.
| Component | Proportion |
| Copper Sulfate | 1 tablespoon |
| Vinegar | 100 grams |
A gentle chemical method is used to remove complex contaminants from copper coins. It is based on a solution of vinegar and copper sulfate. The only drawback of this method is the strong smell of vinegar during the process.
The recipe for the solution is simple and requires precise adherence to the proportions.
The key to preparation is proper heating. The solution needs to be warmed but not brought to a boil. It is important to ensure that all copper sulfate crystals have completely dissolved. If not, the remaining crystals can damage the coin's surface, leaving shiny spots on it.
The cleaning process begins by immersing the coin in the warm solution for 15 minutes. A chemical reaction starts almost immediately, indicated by the appearance of bubbles. This first step softens the top, roughest layer of dirt and oxides.
After soaking in the solution, the coin should be periodically removed and rinsed under running water. To speed up the process and minimize the aggressive chemical impact on the metal, mechanical cleaning is employed.
Using special tools, such as a scraper and a fiberglass brush, the softened deposits are removed. This procedure helps the solution penetrate to the denser layers of oxides more quickly and reduces the overall cleaning time. The work must be done carefully to avoid damaging the coin's relief.
Cleaning a heavily soiled coin is a cyclical process. The coin is alternately immersed in the solution for 15 minutes and then the softened oxides are mechanically scraped off. This procedure is repeated several times, in this case, four to five cycles.
With each cycle, the coin becomes cleaner, and the relief becomes more distinct. After removing the bulk of the contaminants, small, hard patches of oxides may remain on the surface as black or green spots.
These residual defects are removed spot-by-spot with a fine scraper (e.g., 0.2 mm). Such delicate work achieves the smoothest possible surface, which is important for the next stage—patination. Prolonged soaking in the solution without mechanical assistance can lead to uneven etching of the metal and the formation of pits.
After the coin is completely cleaned and dried, the final stage begins: patination and conservation. This process not only gives the coin a noble appearance but also creates a protective layer against further oxidation.
For this, a mixture of sulfuric ointment and dry artist's pastel is used. The color of the pastel can be chosen to achieve the desired shade of patina, for example, green or brown.
Immediately after application, the coating may rub off slightly, but within a week it will be absorbed into the pores of the metal and set.
To complete the conservation and give the coin a finished look, you can use medical petroleum jelly. It creates an additional protective barrier against moisture and other external factors, and also gives the surface a slight 'oily' sheen that highlights the relief.
A small amount of petroleum jelly is applied to the coin and rubbed in thoroughly with a soft cloth. After polishing, the coin acquires a fresher, more well-kept appearance. As a result of this comprehensive approach, it is possible not only to clean the artifact of years of deposits but also to ensure its preservation for many years to come.