The pattern in this blade is already so clear you may not even need an etch. You could take a good oil like WD40 and a fine grade piece of steel wool and go over the blade well. This will remove any superficial rust and gunk on the blade and make the pattern even clearer. Once you have done this make sure all the oil residue is off and you may then want to use a VERY thin layer of a heavier oil to protect the blade. If you want to remove the dark spots and pitting, then I would take Barry's suggestion of a polish or etch.
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