Identifying a new E-V category is a much rarer event than discover­ing a new example of an existing category. It takes a true error sleuth.

Upsetting reduces the diameter of a planchet and creates a low proto-rim around its perimeter. Once in a while, planchets get a very different proto-rim.

Such errors are always more compelling when the nature and origin of the foreign object is readily apparent.

The photography skills of collectors and private sellers can vary from outstanding to abysmal. This makes some online error coin purchases a major gamble.

Die alignment errors can in­volve all three axes and planes that define our spatial di­mensions. Dies can rotate, tilt, pivot, slide, or move in combination.

Since 2010 Diamond has tracked an array of misstruck 2000-P Virginia quarter dollars from one deranged press, finding a fifth error type in an eighth die stage.

Some of the most interesting errors happen to be ones that are faint, subtle, or camouflaged. A deliciously stealthy mystery is found on this Ethiopia coin.

Identifying when in the minting process damage is inflicted is important for diagnosis and valuing. Damage that occurs after the strike generally has no value.

Mike Diamond has recently discovered that a pair of his longstanding assumptions about a certain kind of error coin have been falsified.

Not all transitional planchets are what they seem. Other explanations are sometimes more accurate.