If you want a deeper blue/black you need a lot more cycles. Did you sand the metal on the knife? The finest grit that they recommend generally is 320 but when I did my ‘97 Winchester 12 ga shotgun I went down to about 600 grit. It took a long time to do the whole gun, probably about 25 cycles. I used Plington’s Classic American American Rust Blue from Brownells but you can use other acids. Some may just take longer or not cover as well. Also, I have found that some steels turn out very different than others. I took of the bluing of my 1860 Army (Pietta) and polished it and tried the Brownells Classic Rust Blue and it looked so bad that I had to polish it all off again and still have not finished it.