We sell a large volume of pre-owned silver coins and on occasion, these coins have milk spots or tarnish. Understandably, these raise some questions from customers who want to know why they occur, and whether they can be removed. The rule of thumb with any bullion is that coins should not be polished, cleaned or buffed in any way, as this can damage the coin, causing surface damage. Why though do these imperfections occur?
The honest answer is that there is no definitive reason for milk spots. It has been thought that contamination from oils on the skin when coins are handled could be one reason, or exposure to oxygen. Collectors have tried to counteract this by using gloves and keeping coins in airtight capsules or tubes. Although this does make sense and could contribute to the blemishes, we often see coins with milk spots that have never been opened or handled. This therefore seems an unsatisfactory explanation.
Another theory is that the milk spots are derived from the chemicals used during the minting process of the coins. The chemicals that are used are cleaned off during the minting process before the coins are ready for sale but potentially some of the chemical remains on the coin. After a period of time this residue starts to bleed through to surface level, causing the spots.
One way to remove the spots is to rub the coin with a pencil eraser. We do not recommend this as the rubbing removes a layer of the coin exposing the metal to damage, and often leaving the coins with numerous scratches.
This can affect all silver from silver coins and bars to cutlery and ornaments. Often known as “toning” it is a natural process that occurs as a byproduct of oxidisation of the silver. Although it can look unsightly, it is a well-known process and can be cleaned away using silver dip. Dipping silver does work well in the short term, but the addition of another chemical to a coin can in our experience lead to increased toning further down the line.
The good news is that toning or milk spots does not affect the value of the coins. Yes, it can be aesthetically unattractive, and we would recommend that if you are buying for a collection it may be best to steer clear. However, for purely investment purposes the imperfections will not affect the investment; we would pay the same for coins with the milk spots or without. Additionally, these spots sometimes appear after we have sold them; ie. when they are stored at home with a customer. We would still buy these coins back at our usual price if the tarnish is from the natural processes described above.
We do not clean the coins as a matter of course due to the risk of surface damage as mentioned above. However, if customers would like to check with us in advance of your purchase we would be happy to provide information on any silver product that we sell.