Thread: Standard Reference Material for Hanging Hair Test

A lot of the criticism about the use of the HHT to judge razor sharpness has been in the area of the incomparability between people, because the hairs used are different thicknesses, have more or less oil content, etc.

I've been thinking about how to instrument a sharpness test in order to get an objective, reproducible measure that will work at any stage of honing.

To this end, I've looked for replacements for human hair.

I focused on monofilament thread, as this would eliminate structure issues. I got some "invisible thread" in bobbins, with a thickness of 0.004" ( 0.1 mm). Unfortunately this is too light to let any razor I've sharpened cut it in a simple HHT. I will still try to use in an instrumented test or when I get a Lynn-honed razor back.

Another purchase was monofilament thread used in tying flies for fishing. This is Danville's Monofilament Fine, which is 0.006" (0.15 mm) diameter. It's available on ebay at

Danville Monofilament Thread Fine - Fly Tying - eBay (item 230507649553 end time Oct-03-10 14:34:03 PDT)

(auction #230507649553)

It's only $1.09 per 100 yd spool with $2.99 shipping. (I bought 6 spools to average out the shipping.) You might be able to buy it locally at a sports supply store.

This Danville's thread behaves very similar to the human hair I've been using for the HHT. It is slightly more resistant to cutting, but very close in properties.

The only issue is that it's clear, so somewhat hard to see in use.

The good news is that HHT results with this thread can be compared among members here with some idea that similar results should be expected.

I am continuing to look into colored versions of such thread, and into a possible test jig to standardize applied force or allow quantitative measurement.

That does sound like a good suggestion for a standardized test. Keep up the good work.

Perhaps the King of Search "Hoglahoo" can find you the threads

But yes it has been done using a special rig and a scale even...

IIRC it was determined that even this wasn't accurate, for various scientific reasons

http://straightrazorpalace.com/honin...-measurer.html ?

Thanks LEEEeeeeeeeeee !!!

One of the links on your link had it


Initial Sharpness

I think that the HHT, like everything related to shaving, is always going to be a little different for everyone because there are SO many variables. I think it's more important to focus on making the test consistent for you, as opposed to trying to align your HHT to someone else's HHT. That being said, using a hair substitute may be one way to eliminate variables in your own HHT, and I think it sounds like something that would be worth perusing (assuming you do HHT).

Have you seen what hair looks like under magnification? I think you'd be hard pressed to find a thread constructed in such a manner.

But... Maybe if we had a standardized blade that we could standardize a test hair to...
Then we could take the standard blade, cut a standard hair at the correct amount of pressure, and use that hair to use as a standardized test of the razor edge.

It is possible that we would need a pre-standard standard hair to test the standard edge against, to eliminate the possibility of a substandard standard razor.

Originally Posted by HNSB

But... Maybe if we had a standardized blade that we could standardize a test hair to...
Then we could take the standard blade, cut a standard hair at the correct amount of pressure, and use that hair to use as a standardized test of the razor edge.

It is possible that we would need a pre-standard standard hair to test the standard edge against, to eliminate the possibility of a substandard standard razor.

I mean that in the best way possible.

Thanks for all the links to prior art. Apparently others have done a lot of the spadework.

There are obviously a number of factors involved in measuring sharpness:

1. Edge geometry (e.g., angle).
2. Edge condition (erosity, rollover, etc.)
3. Edge durability (during test or replications).
4. Filament structure.
5. Filament polish.
6. Filament strength.
7. Filament ductility.
8. Filament uniformity.
9. Filament microstructure uniformity.
10. Test off-angle.
11. Test deformation rate.
etc.

However, strength testing always involves these complexities. The way around them is to standardize 1) test geometry, 2) deformation rate, 3) test material.

If a test gives a 10% standard deviation or so in the peak force to fracture, then it is as good as it is going to get, and the test then becomes useful in a comparative sense. The links given suggest this is easily attainable by simple setups.

Designating this new measurement as the "Filament Cut Test" or "FCT", there are different possible ways of getting a low peak force. One is that the blade edge has an ideal shape with sharp angle geometry. The other is that the blade has an erose edge geometry that concentrates peak force into a small contact area, causing initial faults that rip into the material. These two different mechanisms should be distinguishable by supplemental microphotographs.

The crux in developing a FCT is that two different people obtain similar results on the same blade edge, or one person obtains the same results at punctuated points in time. This will depend primarily on the deformation rate control. I will start with the concept of the slowest possible rate (~ 1 mm/s). I do have a constant speed screw drive force measurement system I can fire up to compare to a hand driven experiment. This will also be useful to get a snapshot of the force vs deformation curve to fracture.

I think the idea of initial slackness is a good one, but may not be if scraping of the edge along the filament is an issue. I think the length of filament between the side supports may be an issue as well. The farther apart they are, the less propagated stress from the contact points will affect the results.

At least I appear to have passed the first and most important hurdle: Finding a filament supply that is consistent, readily available and free from important idiosyncrasies. Having it match human hair in microstructure is not critical.