Mirror finish on plane irons?

While flattening the back of a new plane iron, I first used a DMT diamond stone, 325 grit. I got the back flat and it had a mirror like finish on it, albeit with some scratches from the rough grit. Still, I could easily see my reflection and things on the shelf behind me.

The next stone I had was an 800 grit norton waterstone. I continued the flattening process with this stone and the scratch pattern was finer, but the mirror finish was gone. It appeared smoother, but it was covered by a grey haze.

Next, I moved to the other side of the DMT stone which is about 1200 grit. Again it got that mirror like finish. So I tried it on a 4000 grit norton waterstone and it got a smaller scratch pattern but it also got that grey haze again.

While I'm sure that the mirror finish is not important to getting the blade flat/sharp it makes me wonder what the difference is. I've seen others with that mirror like finish and it makes me wonder if I am doing something wrong with my waterstones.

You want a mirror-like finish, with no scratch marks on the back at least near the edge. I only polish the last 1/4" or so. This means I don't have to spend as much time on the back at fist, but have to flatten the back as the cutting edge moves back through grinding and honing. I have a short attention span so it suits my style better. You should be able to do that on a 4000 stone although a 6000 and then 8000 would be better. If I'm prepping a new blade, I start off at 220, and work through 800, 1200, 4000, 6000 and finally 8000. If the back is really bad, I take it to the 100 grit belt sander to take off the high points before starting on the water stones. I don't know that you could do anything to your stones except contaminate them with larger grits. Maybe a good soaking and vigrous scrubbing with a nagura stone followed by more rinsing is in order.

I use the shapton stones 100-5000-8000 and have no gray haze condition. It is mirror like with both the 5000 and the 8000.

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Originally Posted by Tom Jones III

Next, I moved to the other side of the DMT stone which is about 1200 grit. Again it got that mirror like finish. So I tried it on a 4000 grit norton waterstone and it got a smaller scratch pattern but it also got that grey haze again.

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Tom, I use Norton water stones and I get the same results you do up through the 4,000 stone. My 8,000 stone gives me the mirror finish you're looking for. That's how I tell if I've really gotten the blade flat. If I get a good mirror finish from my flat 8,000 stone all the way across the blade fairly quickly, I'm done. If there are remaining areas or gray haze, I've got more work to do.

Tom - with my 4000 Norton it gives a dull haze. The 8000 makes it a mirror finish.
Mike

Thanks guys. I'll be getting an 8000 real soon.