Milk spots on Bulgarian silver coins: how to remove them

A reader’s question

Hello,

I have recently started collecting Bulgarian commemorative coins, and your website has helped me a lot. Unfortunately, white spots have started to appear on the coins “140 Years of the Bulgarian Exarchate” and “The Wonderful Bridges”, which I bought from the bank. I don’t know what causes this. I understand that the capsules should not be opened and that the coins should not be cleaned with various products. Is it true that the coins will lose their value because of these spots, if they haven’t already? Please advise me what to do. Should I sell them urgently?

Our answer

White “milk spots” are a common problem on .925 and .999 silver coins, including the BNB’s commemorative coins. They appear months or years after striking – most often because of residues from the solutions used to treat the blanks before striking, and because of moisture. The spots are not a sign that the coin is fake and do not destroy it, but they make it less attractive, especially on proof coins with a mirror field.

There is no need to sell the coins in a hurry. The spots usually do not spread if the coin stays in its capsule, kept dry and at a stable temperature. The video (in English) shows three ways to remove milk spots from silver coins and bullion.

Caution: the eraser and jewellery-cloth methods are abrasive and can leave fine hairlines on the mirror field of a proof coin. If the coin is valuable, ask an experienced numismatist or conservator first, and try any method on a low-value coin only. Do not open the capsule unless you have to.

More on caring for silver coins in Opinion and analysis.