[stonesweep]

Many hobbiest collectors (in my travels, which is of course my experiences) use 100% acetone soak on metals. A brand known as Renaissance Wax is a popular microcrystalline coating used to inhibit reactions (ive been told its popular with knifemakers as well). Ketchup is a great copper/bronze/brass cleaner while we're here, not so hot on nickel, sort of ok on silver. Titanium and zirconium just don't care how you clean them, aluminum is ketchup friendly.

[ceejayoz]

Is there a reason for using ketchup specifically? Or is it just the vinegar ingredient doing the trick?

[stonesweep]

It's an extremely mild abrasive in this form (of vinegar, yep) - some folks dilute baking soda in vinegar, I feel that's too coarse myself. One of the mildest silver polishes I know about and use, Blitz (not Flitz) is still grittier than ketchup in your fingers. I only use organic, free range grass fed no corn syrup ketchup, my metal is pampered. /s ;) (you just use your fingers or qtips for the crevices, then wash in warm soapy water, dry well then plop into a sealed glass jar of acetone for a few days)