Flattening Oilstones

I sharpened plane irons tonight as I cleaned up from the last few projects, and realized that I needed to flatten my Norton oilstone. A little research reveals that many people flatten both oil and water stones on concrete blocks. Others lap the stone flat with silicon carbide powder on plate glass. I have a cinderblock outside, so I'll likely start with that and see how it goes.

While looking for information on flattening oilstones, I also found a great article at Fine Woodworking that covers waterstones, oilstones, and sandpaper as methods for honing.