Previously I have spread regular mustard onto the blade, wrapped it all in plastic food wrap, and left it overnight. Being somewhat worn out after work, and thinking about the 10 stairs I would need to ascend to reach the mustard in the kitchen, I decided instead to grab some vinegar from the cold room in the basement and fill a Nalgene partially with a 50/50 solution of vinegar and water.
I put the knife up to the hilt in the liquid and left it for 36 hours.
I took it out, wipped it with a paper towel and lo and behold I had a nice, rich looking patina. My fingerprints were evident in the coating - next time I will clean the blade with a bit of methanol etc... prior to treating it.
Although I didn't take any photographs of the metal prior to treatment, I am comparing it with a laminated steel Mora (the blade contains rich carbon steel in the middle - hardness about 59/60, sandwiched between slightly tougher, lower carbon steel laminate strips).
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