First, get 2-3 papertowels and get them damp. I would suggest that you wear latex gloves when doing this.
Mix this:
with this:
and some of this or water:
I'd go about 50/50 on the gel/paint. Thin it with water or Windex until it is not as thick, but also not runny. If you go too much gel, it will look gray, just squirt in some more black paint.
Slather that on in sections of the knife. I did each side of the handle/pommel separately. Once it is covered with gel/paint, blot it off with the paper towel in small swiping motions. Go against the 'grain' of the knife detail. For the finer details, I used a dry paper towel to lift the paint. You can also use a q-tip to get into the harder to reach areas.
If done correctly, the paint will stay in the recesses and the raised areas will be free of paint. I went over the knife several times adding and taking away until it was the way I wanted it.
I didn't bother sealing it because I didn't want the metallic to be affected. Under normal display conditions, it shouldn't need a sealer.