I recently got a Vintage Reissue guitar and I was wondering if anybody had a resource on how you go about creating vintage looking Metal parts, as in if I were to replace the tuners with locking tuners and wanted to "Relic" the new tuners to get that slightly corroded look to them. Same thing with plastic parts? I have noticed more and more companies coming out with new stuff that comes in a "Vintage" finish so this may be a lot less of a problem in the future.
Arrawin I haven't found a good way to age chrome but anything that is nickel can be aged by soaking it in a solution of salt, hydrogen peroxide, and bleach.  Plastic can be made to look grimy by soaking it in tea and black coffee and then hitting it with a buffing wheel to wear it down a bit.

This is a pic of a nickel covered pickup that I have aged using the chemical solution I mentioned.  I managed to get the lines where the strings would sit over the pickup by modifying the solution slightly and painting it on.  I won't tell you how I modified the solution for the darker lines because that is a secret recipe.

This is a strat that I aged.  The plastic was done using the technique I mentioned above.  You can see that the chrome is still shiny because chrome always stays shiny but I did manage to age it a little by using some very course buffing compound and deliberately burning through the chrome in a few places to expose brass underneath. 
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