Some pictures showing through making a forced patina on a 52100 blade, though some pictures are missing as I went along. A patina is an oxide layer on the steel and it can help resist rust forming.

Sauces used - English Mustard, Tesco hot sauce, Tomato ketchup.

The process is as simple as dabbing some on and leaving it then clean off and repeat. Most activity happens round the edge of the splodges, presumaby it needing some air to react the most.