Couldn't resist... for post # 100.
I added a bunch to the post I made just before Mark's
#4254.
I hope I wasn't too wordy.. I hate typing

The wavelength of visible light is between 0.38 and 0.74 microns.
en.wikipedia.org/wiki/Visible_light

Modern optical microscopes have a resolution limit of 0.2 microns (about 1/2 wavelength).
microscopyu.com/articles/optics/index.html

Telescope mirrors are accurate from about 1/8th to 1/20th wavelength, with the most common being around 1/10th wavelength. Although, they are often smoother than this.

So if you can get your scratches significantly below 0.2 microns then you should have a very good mirror finish. So my guess is if you can get scratches down to around 0.1 to 0.05 microns, it'll be a superb mirror finish even under a microscope.

It is interesting to think about the above in relation to the size of abrasive particles. Although I have no idea how to go from particle-size to scratch-size (it's too complicated; depends on hardness, shape, friability, pressure, binder, etc.).

Komitadjie's Grand Unified Grit Chart as plotted by Mr. Wizard:
www.knifeforums.com/forums/showtopic.php?tid/904090/tp/7/


Sincerely,
--Lagrangian

Anthony,
Godd stuff.. in theory. Unfortunately you do not take into account the intrinsic reflectivity maximums for a given material. I will send some info tomorrow form one of the premier polishing companies in the world claiming a max of 65% reflectivity for "stainless steel". Of course different limits for different formulations of steel.

In any case, folks using 1000 grit diamonds will not see a mirror finish. People percieving a "mirror" at the 1200/1600 grit level, have a reflective surface, but a ways to go to get to the reflectivity limits of steel. My post was because I was trying to explore how some people say they have a mirror at X grit and others at XXX grit, and what accounts for the difference.

According to Tom and he has photomicrographs at 400x, the 0.17 micron grit of the 10K chosera is where he saw significant reflectivity ... at 400X that is as good as the empirical data that I have seen goes.
I will be intersted to see what can be done with Clays new microscope. I would love to see some sort of hard data that sorts one person's mirror from another's more highly polished mirror.

This is real interesting stuff.. as soon as we figure out that we can polish metal to the degree that we can rival optical mirrors... I can throw away a bunch of pyrex mirrors ground to 1/20 wave and optically coated for 96 to 98% reflectivity...
(of course then you have to deal with coefficients of expansion and other obtuse issues. They did give up on speculum polished metal mirros a hundred years ago...

Of course, then we need to figure out who cares about reflectivity of an edge... sharp is what we want.. polish is just pretty...

Phil

This is the best I've been able to do so far and I've been able to repeat it several times: Polished Edge I haven't had a chance to do it again and put it under the new scope (plus I'm still waiting for the 100x objective to come back from the manufacturer) but I'm pretty excited to check it out once I get back from VT.

I was able to do some measurements at 800x of a knife I sharpened up to the 10k Chosera stones. Check here for the full sized image: 10K Chosera - 800x

For some reason, the measurements are really hard to read there, but they range from .89um to 1.51um. I only measured the major scratches. I'll keep working on how to post the images so that the measurements are easy to read.

RonRobichaux wrote:


To add a bit to this... I sharpened a knife and repeated what you have... 1000 --> 5m --> 3.5m leather, and couldn't get a mirror finish, even with quite a bit of time on the leather. So, probably not possible, at least not in a reasonable time. (Forgot to snap a photo).

I then went back to the 1000 and then went to the new MicroFine ceramic... coarse then fine for about 50 passes with each. (I haven't lapped my stones). Then on to the 5m --> 3.5m leather for about 75 passes each, and got the start of a mirror finish (obviously without magnification)...



Still a bit of scratching, but considering how little time I spent, this would be at least a good start toward a finer/mirror finish, if that's what you're looking for.