How To Flatten Plane Iron Backs
Use a very light coatings of 3M "77" spray adhesive to temporarily glue small 1-1/2" x 3-1/2" rectangular pieces of sandpaper along the edge of a sheet of 1/4" plate-glass.
The paper to use is Aluminum Oxide in grits 50, 80, and 100, and Silicon Carbide (wet-or-dry to you lay people) in grits of 150, 180, 220, 320, 400, 600, 1200, and 2000. I like the SC/ Wet Dry best. The plate glass should be placed with its edge flush to the edge of the workbench. Grits can be skipped, if desired, but more time on each grit will then be required to fully remove the scratches from the previous grit. Using the gradual progression as listed, however, will require only about a minute or so with each grit."
Lap the end one inch of the back of the iron on each grit in turn. You could use it wet or dry. You can place a thin piece of metal like a 6" section of thin band saw blade near the edge and set the Plane Iron on top then hone the back face this way you will only have to hone a 1/4" wide edge on the blade not a large section of the face and you can use long strokes not short stokes if you don't add the shim.
About every twenty seconds or so, stop and brush off the sandpaper with a whisk broom and wipe the blade off on your shirt.
About ten minutes after starting, you should have gone from 50 grit on up to 2000, and there will be a mirror finish on the back of that iron the likes of which must be seen.
How To Sharpening Bevel Edge
Then jig the blade in a Honing Jig of your choice or go it by hand but this is very hard to attain good results --
Clamp the blade down in the Jig, taking care to have the bevel resting on the glass perfectly along both edges. Adjust the micro bevel cam on the jig up to its full two-degree micro bevel setting if you have a Veritas Jig, if not slide back the blade a hair-- and hone away on the 2000-grit
Flip the blade over on the sandpaper several times, hone and lap, hone and lap, each time gentler and gentler, to remove the little bit of wire edge
The resulting little thin secondary bevel should be quite shiny by this time.
Remove the blade from the jig, and perform the "shave some arm hairs off" test, or the sharpness test of your own choice.
Of course, the ultimate test of a plane iron's sharpness is what it does on wood.
When it is all done, peel the sandpaper from the glass and throw it away. Then, scrape the little bit of residual adhesive from the glass with a razor blade, a quick wipe down with acetone on a piece of paper towel, and the cleanup is done in a minute.
No oil, no water, no mess, no glaze or flatness problems to worry about, and a cutting edge that is Scary-Sharp (TM).