The knife pictured above and below was soaked in bleach for about 35 min.
I hand sand to 400 grit, coat in cold blue and then soak in bleach. Once they come out of the bleach, I dry them off and clean the bulk of the rust off with a wire wheel. Once all the big crusty rust is knocked off I neutralize with water/baking soda and then hand sand back to 600 grit. I then re-blue and sand the flats lightly leaving the bluing in the pits. It's a long process but I really like the "rustic" effect.
O1 gets pretty darn rusty in a short amount of time in bleach.