I used a mustard/coffee grounds method to form the pattern. Apply mustard evenly and let sit for about 20 minutes. Rinse, repeat. I had some used coffee grounds that I would bury the knife in between the mustard applications. Did it about 15 cycles to get that pattern.
I initially just used the knife to try and get a natural patina, but some rust started showing under the paracord wrap and on the blade after I cut up a rotisserie chicken. I hand sanded the entire knife and decided to do the mustard thing to inhibit future rust.