How Can I Make A New Coin Look Aged?

Why would you want to do that? That would just lower the value of the coin.

I'd do the same thing they do to furniture. Beat it with a hammer and scrape it on the ground, maybe put it in a vice and get some marks on it. If it's gold plate, the surface is gonna come off.

Although I do agree pure gold is pretty non-reactive stuff, most gold coins were not pure gold. The copper alloys in many give an orangish hue after many years to decades, depending on their environment. There is actually mention of this briefly in the Charlton Catalogue in the section on coin grading. This type of toning does not detract from a gold coin's grade.

Similarly, these copper "particles" may not have thouroughly mixed in some specimens, causing orange to brown to purplish spotting. Again, most suggest that this should not detract from the coins grade. I have a 1/10 A.G.E. with this condition and the coin is of course modern. In it's case I would disagree because it definately detracts from the look of the coin, and I certainly would expect questions if I were to ever sell it!

I won't dismiss the motor oil idea... there's alotta caustic nasties in there that would surely discolour alotta metals. >>> edit... I've posted this link on toning silver before, but since many "recipes" are simply dirt... well, have a look and decide for yourself. VVV
http://www.coinsite.com/content/ori...p0000080.htm