A double-die coin is a coin that has been through the design-printing process twice, leaving it with a double layered effect. These coins are not cut on purpose and are therefore very valuable in many instances. If you come across a coin that is possibly a double-die, you need to identify whether it actually is or not to establish if it is worth your time and money. There are a few means and ways of determining the true status of your coin, so run through as many of them as you have to until you are comfortable with the diagnosis.
Set the coin with the head side facing up. Place the magnifying glass stand directly over the coin so you can easily see the details.
Look closely at the overall look of the printed image. If the edges clearly appear doubled, then you have a double-die coin.
Inspect the numbers of the date for smudges or over-thickness in the lines. If some of the numbers appear blotchier than others, you are seeing polishing errors, not a double-die image.
Check the small uppercase letter directly below the date. Look carefully for a second letter below the first, as this is an easy-to-spot indicator of a double-die.
Look at the serifs for small horizontal splits or breaks, which will give away the presence of a first die below the top one. Serifs are the small flourishes on the corners of the letters.
Follow the edges of the letters and designs for inconsistencies compared to similar coins. If the differences are found commonly throughout the coin, it is very likely a double-die.
Check the insides of letters such as D's and O's. If there are dips or bumps inside the letters where the coin should be smooth and flat, this is probably a sign of being printed twice.