Love this excerpt from the Lancaster Bee’s “Out of the Past” segment.  Seems like the impermanence of some fountain pen inks was still an issue a few years back with the introduction of bulletproof inks by Noodler’s and other ink manufacturers.

In the early 1900’s the solution was provided by companies such as Security.

• The latest swindle is carried on by means of a double fountain pen, one end of which is filled with good substantial ink, the other with ink that fades away in a day or two. The sharper writes his agreement, contract or whatever particular way he may have chosen, with ink that will not last. In a few days he has a slip of paper with nothing but a signature over which he can write a note and easily turn it into cash. Look out for the fountain pen swindler, for he is dangerous.

http://www.lancasterbee.com/news/2017-04-27/Editorial/Out_of_the_Past.html