NCW Info

The Invention Of Green Ink


The green ink that has been used since 1862 to print U.S. banknotes was invented in 1857 by Thomas Sterry Hunt while he was a professor at McGill University in Montréal. Hunt was the staff analytical chemist of the Canadian Geological Survey and it was during his time in this position that he started becoming familiar with chromium-containing minerals. For the banknote ink he proposed the use of chromium sesquioxide, Cr2O3, also known as chromium trioxide.

This may not seem like a major invention but this green ink is the reason why so many counterfeiters are unsuccessful at reproducing U.S currency. This green ink also cannot be destroyed by acid, base or any other agent. The green ink has another very important characteristic: it cannot be copied by photography.

It seems that Hunt did not benefit as he would have hoped to from his invention. He sold his invention to the United States government for much less than it was worth, considering it has become very widely used. In a letter to a friend he wrote, "As yet it has been rather more trouble than profit." Hunt's invention also led to the nickname "greenbacks" for American currency.