Thanks for the info on forcing a patina. I'm afraid I can't do it now though, because I gave this knife to a buddy of mine

. A may try forcing a patina again in the future on another knife though.
From what I read here at BF, there are two schools. One school uses a carbon steel blade for whatever tasks it's needed for, and the patina develops naturally over time and use. The other approach is to force it.
The appeal of the first approach is that it produces a result with loads of character and history that some feel is more authentic and perhaps even more honest. I don't disagree with that, but I tend toward impatience. Also I don't do a lot of food prep, which would bring the carbon blades into frequent contact with things that would develop a natural patina.
So I opted for the forced approach to get the protection. (Patina will help prevent rusting.) I read at BF about several ways to force the patina, but vinegar appeared to be the key ingredient and I figured I'd start with that. In addition, heat usually makes chemical reactions go faster, so I put a jarful of vinegar into the microwave, hit 45 seconds, then gave it some seconds more to bring it up to hot (but not boiling).
I put the cleaned blade into the vinegar and saw the darkening start right away. I kept it in the vinegar until it reached a medium gray overall. Then ran the blade under the tap, and called the job done.
Now there are different grades of carbon steel, and they may react differently. And degrees of heat treating may make a difference, too. I don't know. This was a fast-and-dirty approach but it worked, and I'd start with it again next time I need to patinate a blade. All this is to say that you may get different results, so let's call it the YOYO method (You're On Your Own).