Depends on the material started with.
For plain carbon steel, heating it red hot (until a magnet won't stick) and plonking it into a can of water, will make it as hard (and brittle) as it will get. Unfortunately, if you do that to an oil hardening steel, it will often crack or break, so you need to figure out where you are starting from.
There are water hardening steels (W-1, etc), Oil hardening (O-1), and air hardening (A-2) available in the form of rods with a ground surface finish.
Check out KBC Tools online catalog, and look for the drill rod. Starret sells drill rod and flat stock in various sizes too. Expensive, compared to bulk steel, but sometimes you really don't need much and when the work is 95 percent of the cost of making it...
I'd suggest polishing it up with a strip of emery while it is hard, then applying heat to the shaft behind it, and plonking it back into water when it turns straw colored at the tip. Provided you are using water hardening or plain carbon steel, anyways.
Google Heat Treat Colors, to see some pictures of what that looks like. If your machinist has any experience that way, talk nice to him and see what you can come up with.
Cheers
Trev