Try a carbide steel for higher RC alloys

[Geode]

I bought a carbide steel from Lee Valley for about 5 bucks. It does quite well with the M2 and BG42 steel blades that I have. I believe that carbide is a good deal harder than the larger steel Lee Valley sells - both are an excellent bargain.

To answer your original question - smooth steel. Otherwise I would burnish a blade using the fine ceramic rod on my Spyderco Sharpmaker.

Geode.