HOW TO DETECT IRREGULARITIES ON COINS

Rim nicks

Get into the habit of first examining the rim of a coin. This will prevent you from omitting the most vital aspect of your examination of any coin. Rim nicks can reduce the value of the coin to a large extent, depending on the seriousness of the nick and the general grade of the coin.

Rim pin mounted coins

Look for pinholes in the rim, which would make the coin "ex-mount". Examine the milling carefully. Any irregularities might indicate that a pinhole has been repaired. If you come across an irregularity look for other irregularities at the corresponding positions. If the irregularity is at 12 o'clock, there might be another at 6 o'clock. If there is no corresponding hole, the damage may be other than ex-mount damage. A favorite combination is 3 o'clock and 9 o'clock, or at four equidistant points. Although the face of the coin may be perfect, the ex- mount coin reduces the value considerably.

Ex-mount traces on the face of the coin

Coins may have been holed or pierced to wear as jewelry. The hole could have been cleverly repaired. Look for blemishes in the center of the coin or two at diametrically opposite sides of the coin. 

Ex-clasp coins

Clasps or holders were used with the intention of mounting coin without damaging them. Coins should be carefully examined since it is difficult to detect the damage to these coins.

Silvering

The coin has been treated with some chemical, most often to match it with its mounting or for other reasons. The coin will have an unnatural appearance.

Gilding 

Gold coin were frequently mounted and gilded to match the brooch into which they were mounted. Gilding leaves a thick coat on the coin, which affects the clarity of the detail.

Polishing

The coin might have been polished with a commercial cleaner or have been buffed. The coin is recognized by an unnatural shininess. Polishing may briefly improve its superficial appearance, but such abrasive action will destroy the patina and reduce the fineness of the high points of the surface. On first view the coin looks beautiful, but its value has been impaired. 

The extent of the diminutions in values can vary substantially. It often takes an expert to discern variations in irregularities, and reach an overall conclusion.