Why doesn't "Nic a date" restore dates permenantly???

I've been googleing "nic a date" posts, and from what I can tell, the
date appears on the nickel when you put a drop on there but it's only
temporary and the date vanishes again after a while, after you wash the
drop off.

This is too bad. Does anybody have any methods of making the date stay
"readable" on the nickel permenantly? Like instead of rinsing the drop
away with water, you rinse it away with something else that will
neutralize the acid or something and leave the date on the nickel?

I'm not suggesting that I'd try to pass of my nickels as regular dated
nickels or anything, it's just that I don't want to go through all the
trouble of recovering dates only to have them disappear again.

Any and all info greatly appreciated. THANKS!