Okay, I'm not crazy. I swear I saw a post on this board where a guy was antiquing a sword by immersing it in an etching solution, and either the sword or the solution was hooked up to a car battery.

Does anyone have any idea what I am talking about? It is not the one where etching a medieval character into a blade is demonstrated, but rather antiquing an entire sword blade.

Am I imaging it? Was it on another board?

Look up oxidation / reduction reactions

Try doing an Internet search for Electrolysis. It is usually used for cleaning objects but it can be used for speeding up the rusting of metal too. You would have to be very careful though, you can destroy the whole blade with this process. There are serveral clips on Youtube as well.

It works just like rust cleaning by electrolysis, a nice method that I use for some time for cleaning my old, rusty bayonets:
http://myweb.tiscali.co.uk/andyspatch/rust.htm#method

To age the piece you have to reverse the current, you connect the positive lead (anode) to the blade. Be careful, try it first on something inexpensive, ex. piece of steel.