Identification
Die deterioration doubling is a result of a few simple causes, but it can be difficult to positively identify. There are a number of different features which appear similar, but the characteristic traits of each are easy to identify with practice. Die deterioration doubling is often mistaken for hub doubling. The causes of the two types of doubling are different, but their appearance on the finished coin is often similar. Die deterioration doubling appears most often around the mintmark and date because they are alone in the field. When it occurs in other features, like an image of a bust, it looks more like a weak strike than doubling.
Close examination of affected features show that the doubling is extremely irregular. This is because the coin metal does not flow from just one direction, but flows and produces wear on the die from all sides. There is no definite shape, and it can take on several different but similar appearances. It often looks like a thin metal shelf or spreading spot. It can also make lettering appear thick and twisted. There are no crisp lines affected, but things generally look bloated, enlarged, blurry, twisted, and damaged. This is different from hub doubling, because hub doubling appears as a crisp secondary image, rotated minutely from the original. When casually glancing at a coin, the difference is not easy to tell, but when magnified, the difference is obvious on most coins. Another easy way to tell hub doubling from die deterioration doubling is the presence of notched serifs; the small flairs on the ends of letters will appear distinctly separated with the former, whereas they appear just blurry and washed out with the latter.
Read more about this topic: Die-deterioration Doubling