From
this page,
QUOTE
"Eternal" refers to any Noodler's Ink that resists the effects of time - moisture, humidity, UV light, acids, water exposure, and many common detergents such as dish soaps and household ammonia, as well as alcohols and acetone (which conventional ball point pens have no resistance to - often rinsing off a newly written check within 8 seconds of being washed with acetone). Many Noodler's inks such as "eternal" and "bulletproof" inks are made with the ideal of reaching out as far into immortality as the written word permits us to reach
[...]
"Bulletproof" refers to any Noodler's Ink that resists all the known tools of a forger, UV light, UV light wands, bleaches, alcohols, solvents, petrochemicals, oven cleaners, carpet cleaners, carpet stain lifters, and of course...they are also waterproof once permitted to dry upon cellulose paper.
[...]
Regards, Myles.