I don't know if it's been discussed before, but here is a simple way to age new fasteners. I lost an original bolt that fell into the engine bay. I know it will show up eventually, but for now I replaced it with an aged new bolt.
The aging process only takes a couple of minutes and involves heating the bolt with a butane torch until the zinc plating changes color to a whitish gray and then immediately dousing it in oil (I used Marvel Mystery Oil because that's what I happened to have, but any oil works). The aging isn't just burnt oil (it won't wear off), it permanently changes the zinc plating. I suspect that the modified plating will still prevent corrosion (it seems like the zinc is chemically changed rather than removed), but that's just a guess on my part.
Photos below of the tools and "aged new" versus "unaged new" bolts:
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