I received this question in episode 3 of the Ask Brian Boggs Show:

I’m thinking of purchasing a set of sharpening stones. Do you recommend diamond stones, or water stones?

This is an age old question that will never stop being asked, and it’s probably good that it isn’t because as our tool metallurgy evolves, our stones will need to evolve. When I first started learning about Japanese tools, for example. The really best Japanese chisels were recommended to be sharpened on a certain water stone from a certain mountain because that specific steel responded best with that specific grit. We don’t really talk about that much in our sharpening lore now. We’ve starting to use alloys. Most people will still sharpen them either on sandpaper, or on a water stone. I don’t think you’re going to get a great cut from a water stone on alloys. It just doesn’t seem to cut the metal uniformly like diamond does.

Unfortunately, the diamond stones that are available, in my perspective, are not great quality tools. I use them. I happen to have gotten a good deal on some. We use them for our initial shaping, and then we go to a diamond pace on lapping plate, which is a cast-iron plate designed specifically for lapping with diamond compound. The cast-iron has a specific hardness, and porosity, that works well. The diamond particles will embed themselves in the pores, hold still, and lye to get a really nice cut. That’s the best edge, or the best stone, for getting really fine edges on alloys. I think for O-1, as well. I don’t think diamond beats water stone for O-1 steels. Certainly for alloys, which for most of our blades are alloys. If you’re gonna use a diamond stone I strongly recommend getting some diamond abrasive, which I believe Woodcraft carries now. Beta Diamond in California carries it. There are a number of suppliers of diamond compound. It’s a paste, and you can get different grids. I generally finish with 4-micron. Then I’ve gotten a flattened maple block that I use the 4-micron diamond compound on, and that gives me my final polish.

One of the things I don’t like about water stones is the creation of mud. While that is often pitched as an advantage, you create a scenario where you’re not just getting a clean cutting environment, but it’s a erosion like environment where the mud being above the of the stone, and not fixed to the stone, erodes the edge, and rounds it over slightly. So you can’t get a true flat all the way to edge. The same is true, actually, with diamond compound on a lapping plate. It’s a smaller particle, and the lapping plate is hard. It’s less of an issue getting that roundness at edge than I have found with water stones.

For that reason we use, almost exclusively, diamond stones here. The rounding over issue, and the hardness issue, and the ability to cut alloys, as well as are warranted. The argument will never stop going on. There’s always somebody coming out with a new sharpening system, or a theoretically better diamond stone. I don’t think conversation should end. Try out new stuff. Different people have different response to these stones, I think. The water stone takes more skill to use really well to maintain it’s flatness than the diamonds do. That’s a whole different story. Some people love developing that skill, and hats off to them.