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The saya (scabbard) of J swords is also made of Paulownia wood which absorbs moisure protecting the blade.
There's an idea make a razor box out of it. :idea:

Carbon steel will darken no matter what you do & carbon steel will begin rusting at 40% RH . Oil will however prevent rust but not tarnish.

I reckon people who don't oil their razors have some...