Abrasive Particle Sizes

[Doug Hepler]

Hello,

This is a question from curiosity. I'm posting it here because this is where the sharpening gurus visit. I was browsing websites of guys who like to shave with straight razors. They are more obsessed with sharpening than we are (I had not thought that was possible.) One of the people who posted was a bit indignant because he had found out that Veritas green rouge might contain some fraction of particles that are larger than the labelled 0.5 micron. I guess he thought they were all the same size.

Well, that brings up at least two questions: (1) how in the world does one "sieve" abrasive particles that are down in the micron & submicron range? I used to do some air sampling so I'm going to guess that they use some kind of air suspension method. (2) What is a typical distribution of particle sizes in a synthetic abrasive mixture, whether it is a waterstone, abrasive paper, powder or paste?

Just curious

Doug

[Patrick Chase]

Hello,

This is a question from curiosity. I'm posting it here because this is where the sharpening gurus visit. I was browsing websites of guys who like to shave with straight razors. They are more obsessed with sharpening than we are (I had not thought that was possible.) One of the people who posted was a bit indignant because he had found out that Veritas green rouge might contain some fraction of particles that are larger than the labelled 0.5 micron. I guess he thought they were all the same size.

Well, that brings up at least two questions: (1) how in the world does one "sieve" abrasive particles that are down in the micron & submicron range? I used to do some air sampling so I'm going to guess that they use some kind of air suspension method. (2) What is a typical distribution of particle sizes in a synthetic abrasive mixture, whether it is a waterstone, abrasive paper, powder or paste?

About once a year somebody "discovers" that the green compound contains larger alumina particles in addition to the advertised 0.5 um CrO. That's why LV's literature claims that it "leaves a scratch pattern equivalent to 0.5 um" instead of claiming outright that it's 0.5 um.

I don't know how submicron sieves work, although I can think of a couple other methods offhand (electrostatic, settling/sedimentation) in addition to the one you cite. There are various medium-specific specs, such as FEPA for sandpaper, JIS 6001-98 for waterstones, and ANSI B74.20 for "sub sieve" diamonds with grains too small to be specified via sieving. Each of the controls the ends of the distribution in some manner as well as the center. IIRC FEPA and JIS both limit the 97rd and 6th percentiles of the size distribution. This older version (https://archive.org/stream/gradingofdiamond00unit/gradingofdiamond00unit_djvu.txt) of B74.20 is worth a read to get a feel for how such specs work.

[John K Jordan]

What I'd like to know is how best to examine and measure the grit particles. I have a variety of compounds in both stick, paste, and powder and would like to know the particle sizes.

I have some laboratory microscopes, each with an oil immersion lens for 1000x magnification. I'm imagining I could scrape some powder off a stick onto a glass slide. Has anyone tried this and will it even work? Is there a better way?

I don't have a reticle and I'd prefer not to spend a couple of hundred on a stage micrometer to calibrate. I suppose that the actual measurement wouldn't be nearly as important as determining the relative sizes of the various compounds so maybe I can get by without calibrating and just compare samples. I do have some 3 micron sandpaper that might give me a rough idea of what I'm looking at.

Any advice?

JKJ

[Patrick Chase]

What I'd like to know is how best to examine and measure the grit particles. I have a variety of compounds in both stick, paste, and powder and would like to know the particle sizes.

I have some laboratory microscopes, each with an oil immersion lens for 1000x magnification. I'm imagining I could scrape some powder off a stick onto a glass slide. Has anyone tried this and will it even work? Is there a better way?

I don't have a reticle and I'd prefer not to spend a couple of hundred on a stage micrometer to calibrate. I suppose that the actual measurement wouldn't be nearly as important as determining the relative sizes of the various compounds so maybe I can get by without calibrating and just compare samples. I do have some 3 micron sandpaper that might give me a rough idea of what I'm looking at.

Any advice?

JKJ

The B74.20 standard for diamond grading is explicitly written for grading by microsope (after acid/base washes to get rid of adulterants etc), but I'm not sure I'd bother. One obvious challenge here is that the visible range is centered at 0.55 um or so, so 0.5 um abrasives are right at the edge of achievable resolution. You can spend a LOT of money going down that path, and end up with not much to show for it.

IMO for somebody like you or I it's better to focus on the edge or (better still) the wood rather than the abrasive, and just stick with it once you find compounds/stones/papers/films/etc that work for you.

On other remark: The optical community are not at all tolerant of surface deviations, so another option here is to buy ultra-tightly-graded powders from their suppliers and mix your own pastes/compounds. There are a couple specialty sellers out there that appear to be doing exactly that. Stewie got some pure 0.5 um CrO paste from one of those a while back IIRC.

[Mike Baker 2]

I am one of those straight razor users/honers.
One thing that needs to be pointed out is that there are different "factions" of straight honers. Kind of like there are different ones in the woodworking community. There are those that think this technique is proper, and this one is not, and vise versa.
There are those in the straight honing community that completely eschew pastes of any kind, and think if one cannot get a good shaving edge off of a stone and a clean strop, one needs to refine their technique until they do.
These are the majority of the guys squawking about the difference in refinement in pastes.
But there are guys (and gals) that shave with a straight but don't want to learn to hone, or go through the expense of purchasing the stones needed. They send their blades out to be honed two or three times as year. For those, IMHO a pasted strop once or twice a week can keep the edge going a bit longer between honings, and is perfectly appropriate. I also believe it is appropriate for a new honer who is not quite "there" yet with his technique. He can finish on a bit of paste and get a good shave while learning how to hone to a better level without them. The kind of refinement a straight requires takes time to learn.
There are also those who through experience have found that some paste is not the equal of others. For instance, I would never go down to Lowes or Harbor Freight, or any general woodworking site, to buy chromium oxide or other paste to use on a straight. They are not refined enough. A straight razor edge must be refined far beyond what any of us probably would use for woodworking tools, as you are looking for comfort against the face when shaving, not just sharp. What most people consider sharp is no where close to what is needed for a straight. I would call it refined, not sharp. You get to sharp rather quickly. Getting to smooth is the rest of it. But I digress. There are specialty places, mostly shaving vendors, that carry a more refined crox paste specifically made for the straight.Much better quality control, etc. A lot of the chatter about the difference in particle size in pastes in the straight razor community is an overabundance of caution to newer honers/users NOT to use the wrong crox paste.