The green ink on the back of 1861 demand notes was used as an anti-counterfeiting device. It would not photograph and could not be used to make plates.

The first United States federal currency, the demand notes of 1861, were given the nickname “greenback” because of the fraud-preventing green ink used on the back of each note.

On these, as well as on some of the first legal tender notes of 1862 to 1863, a close look will reveal a patent date mentioned; for example, PATENTED 30 JUNE 1857 on the demand notes. This date refers to a private patent for the green ink that was used to thwart counterfeiting, since it was thought to be resistant to tampering and difficult to duplicate.

If you look closely at the story of this ink, says Graham Iddon, a writer for the Bank of Canada Museum, it turns out that America’s greenbacks have their roots in Canada, thanks to ink that was invented there.

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Iddon writes in a blog for the bank that the advent of photography in the 19th century made counterfeiting easier than ever. Many notes were printed with black ink only, and a reasonably adept crook could then make fakes of these through photography, without even engraving a plate.

Bank note printers responded by using more colored inks. Counterfeiters countered by removing the colored ink, photographing the black portions that were left, and reprinting the colored parts. The printers then had to find an ink that would be harder to remove.

Enter Dr. Thomas Sterry Hunt, an American teaching at Laval University in Quebec City. In response to a request in 1857 from the president of the counterfeit-prone Montreal City Bank, he invented “Canada Bank Note Tint” ink made of an “anhydrous sesquioxide of chromium.” Iddon explains that “chromium was super-heated in a near oxygen-free environment, where it would decompose. The resulting material was then mixed with linseed oil to make ink in a green shade similar to oxidized copper.”

His invention was proven hard to either chemically or physically remove from paper. But Hunt could not patent the ink in his own name since he was not a British subject (Canada did not become independent until 1867), so a chemist with the Montreal City Bank, George Matthews, filed a patent for Hunt and forwarded him the royalties.

The ink was tested by a number of chemists who found it up to its intended task, but then one found it could be removed by boiling a note in sulfuric acid. When another chemist found a way to remove the green ink while leaving the rest of the note untouched, Iddon says that in August 1857, “the Executive Committee of the Association of Banks for the Suppression of Counterfeiting voted, unanimously, that the Executive Committee cannot recommend to the associated banks the Patent Green Ink.”

That did not have an impact on the Treasury Department or its private bank note printers, and four years later, the “greenback” was born.

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