Green Maned Lion
Engineer
Blue and blue-black inks in many ballpoint and some rollerball pens have iron in them. As such, they are slightly magnetic. A computer with a magnetic page reader can read them.
There are many, many different kinds of ink. I am a pen collector, and I think I have something approaching 20 different black or blue-black inks in my ink drawer. Iron galls, copper galls, india, (none of which should ever be used in a fountain pen, by the way), water-based inks, oil based ink, alcohol based inks, and Noodler's Bulletproof black. Which actually molecularly bonds with cellulose sugars, causing the markings by such ink to be completely permanent- don't spill it on a cotton shirt, cotton is the purest form of cellulose.
I am not sure why precisely Amtrak would require black ink. But I can tell you there are literally hundreds of solid reasons why they would.
There are many, many different kinds of ink. I am a pen collector, and I think I have something approaching 20 different black or blue-black inks in my ink drawer. Iron galls, copper galls, india, (none of which should ever be used in a fountain pen, by the way), water-based inks, oil based ink, alcohol based inks, and Noodler's Bulletproof black. Which actually molecularly bonds with cellulose sugars, causing the markings by such ink to be completely permanent- don't spill it on a cotton shirt, cotton is the purest form of cellulose.
I am not sure why precisely Amtrak would require black ink. But I can tell you there are literally hundreds of solid reasons why they would.