Why is the Greenback Green?by Franklin Noll on 07/31/20
The short answer is that green ink was a security feature in the mid-nineteenth century.
In the 1840s, the search was on for a banknote ink that could not be removed (rubbed out, bleached, etc.) from a note without destroying the paper substrate. Such an ink would deter counterfeiting, which at the time was primarily accomplished by changing a number on the note or by bleaching the ink off a note and printing a new face on the cleaned security paper.
One chemist discovered such an ink. And, the underlying chemical caused the ink to be green. So, green was not an aesthetic choice. The color was dictated by chemistry. This ink formulation was patented in 1857 and became known in the banknote industry as patent green ink.
When, during the Civil War, the US Government needed its first banknotes produced, it turned to the American Bank Note Company in New York. These United States Notes were produced using this patent green ink. But, this ink was only applied to the front of the notes. This was done because it was expensive.
So, why are the note backs green? The problem with patent green ink is that it bled through the paper, creating a reverse image on the back of the banknote. To cover this up, the US Treasury had the backs of their first banknotes extensively printed in green. And, upon examination, one can see that the expensive patent green ink on the front of the notes is a lighter color than the cheaper dark green ink used on the back, which was not secure.
Hence, greenbacks have green backs because the faces have patent green ink on them.
The nickname, “Greenback,” can from Union Army troops who received the notes in their pay packets. Soldiers being soldiers, they just called the notes Greenbacks, because the backs were green.
The use of green backs on these first Government bank notes started a design tradition that lasts until today.