The note is what is known as a blanket impression error, also called, a bit misleadingly, an “offset printing” error. The mistake that resulted in this error actually occurred several sheets before the sheet on which this note was printed.

This error note has you seeing Hamilton double, if a bit faintly and backwards once, but it did not occur the way you might think it did.

An error note that has you seeing Hamilton double, if a bit faintly and backwards once, is an affordable mistake that did not occur the way you might think it did.

The Series 1977 $10 Federal Reserve note has normal face and back printings, but also a second version of the face on the back of the note. This extra image is not only on the wrong side of the note, but it is backward as well — a mirror image of the face side.

You would be forgiven for thinking that the extra image “bled through” from the face to the back of the note; that is a common first impression for individuals unfamiliar with how paper money was printed nearly four decades ago when the Series 1977 notes made their debut. However, you would also be wrong.

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The note is what is known as a blanket impression error, also called, a bit misleadingly, an “offset printing” error. The mistake that resulted in this error actually occurred several sheets before the sheet on which this note was printed.

When this note was printed, the backs and faces of 32-note sheets were printed in separate operations. First the back of a sheet was printed and then the face, with some time granted between the two printings to enable the ink on the back to “cure” (it dried almost instantaneously, but 24 hours or more was allowed before the sheet was printed on the other side so it became fully stable and unlikely to smear under pressure).

The sheets were printed by curved printing plates affixed to a roller, with a second roller of equal size covered with a flexible blanket that impressing the linen-cotton paper into the ink-filled grooves of the intaglio plate. A second or less time passed from when one side of a 32-note sheet was printed before the next sheet passed between the two rollers, and the next sheet, and the next sheet.

At some point, however, there was either a gap in the sequence of sheets or one of the sheets was folded. In either situation, the ink-filled plate came into direct content with the blanket on the other roller, the result being the transfer of the ink to the blanket.

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As new sheets continued to be fed into the press in a normal fashion, the ink on the blanket was transferred to the already printed backs of the next dozen or so sheets, until all of the ink was used up. The first sheet would have had the darkest printing, with the ink of the same darkness as the normal printing on the face. Subsequent sheets would have gotten increasingly fainter impressions. Obviously, the transferred ink would be a mirror representation of the normal image on the face.

Blanket impression errors used to be pretty common; I have found them in circulation myself. The illustrated note sold for $164.50 in Heritage’s Feb. 28 Tuesday Internet Auction. It is graded About Uncirculated 50 Exceptional Paper Quality by Paper Money Guaranty.