I like that look alot what did use.
I pretty much threw the contents of my fridge at it. First a total slathering in yellow mustard, which made it sort of irregular and weird so I washed it off.
A soak in white vinegar followed, after which I cut up a tangerine and laid the slices on the blade. After this was done, it didn't look right at all, I had a problem with overlap and parts that didn't contact. Washed it off, another vinegar dip, too.
I did a regular dot pattern of more mustard over the whole thing, left to hang overnight, rinsed it off to reveal a more regular pattern of overall mottling. Needed more screwing around, though.
Tried again with the tangerine, this time carving chunks of fruit into blade-shaped segments that fit together, using the lot as a sort of citrus sheath.
Finally, by hand I "stippled" lime juice onto the blade surface, let it dry and then stippled a second coat over it. This was left to dry/etch in overnight. In the morning the thing looked about as it does above, but a little dry with residue from all the nasty shit I had piled onto it. A thorough wash up followed by a nice mineral oil treatment and a paracord wrap and voila, easy as pie.
FYI: stripped it before hand with some spray on paint stripper. There's a buttload of threads about stripping off the coating, so check there before I build another wall o text.