Got a question that's been banging around in the back of my head for a while. I remember hearing that currency paper has basically been the same for at least a century. Sure, we've added watermarks and security strips, but the paper itself is the same. Yet a currency pen - the type used by cashiers to check for counterfeits - that I have says it's good only after 1950. Why?
I can only guess that there are different chemicals added to prevent mildew (which I know they do now), etc., or used in the binder substance, or maybe the paper is prepared differently - since the 50s they use the dry process (vs wet printing). I am sure the make up of the paper (cotton fiber) is the same, but there have been changes for sure. One case is the threads - I have a Series 1917 $1 with a bucket of blue and red fibers running down one part of the bill.
Prior to Series 1950, the paper used to make currency was made in part from linen rags. After Series 1950, the paper is made in part from cotton cloth scrap. Today, the cotton cloth scrap is entirely cuttings left over from the manufacture of blue jeans.
