Design Error. A mistake in the concept of a coin or medal design or its modeling; an incorrect device or detail appearing on the final rendition. Such error as an incorrect device, erroneous clothing, and incongruous object, or any inaccurate or inappropriate design element is usually the fault of a lack of researching the subject adequately. An extreme example would be to show an airplane in the sky of a 19th century or earlier scene. A less obvious example is the smoke blowing one way and a flag flapping another. The artist gives his understanding of the visual object, which, in fact, may be inaccurate.

Should such a design error occur and progress through all the stages of die making and pieces be struck, these struck pieces could be considered a transitional design or prototype. These are corrected with a new design, and, of course, new dies for the production run. To the credit of the thousands of coin and medal designers of all time, however, few such design errors exist. What is more susceptible to fault are the errors of inscription – incorrect lettering, misspelling, wrong figures, the blundered inscription or blundered legend. The artist's concept ideally should be edited both as a sketch and, of course, as a final model before dies or molds are made. See entry on errors (for other kinds of errors, as blanking, striking and such).