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<p>[QUOTE=&quot;mikediamond, post: 339158, member: 1859&quot;]Surface film doubling occurs when an oily planchet (or a planchet struck by an oily die) expands during the strike.&nbsp; The area first touched by the die escapes to the side as the downstroke progresses, leaving behind a track.&nbsp; This usually has higher reflectivity than the surrounding metal and appears dark in photos.&nbsp; Usually the outline is vague, unlike the sharp outline seen here.&nbsp; Surface film doubling is best seen in coins struck out-of-collar (broadstrikes and off-center strikes), but subtle manifestations can occasionally be picked up in coins struck in-collar.</p><p><br /></p><p>Surface film transfer is more complex.&nbsp; If an oily planchet is struck once, shifts position, and is struck again, an oily image of the first strike is transferred to the field of the die.&nbsp; This is then transferred to the next coin that is struck as a shadow image.&nbsp; Surface film transfer tends to be sharper, like what we see in this Canadian dime.&nbsp; So if I had to guess, I&#039;d go with this hypothesis.&nbsp; I&#039;ve only seen two examples in U.S. coins, but it has been experimentally duplicated in coins struck in private mints.&nbsp; Ken Potter calls it &quot;contaminated die doubling&quot;.[/QUOTE]</p><p><br /></p>

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