back of the head hair test

[whirlwynds]

anyone do this? what is the purpose? to see how the knife edge grabs the hair follicles?

why not just try it on a natural bristle paintbrush? I guess because you only have one-way feedback and not two-way.

 

[daveb]

Me thinks you're over thinking this. As you get started, find a good utuber mentor - JKI and/or Knife Planet are both good. You'll be developing proficiency when the knife is sharper when you're done than when you started.

 

[Southpaw]

I have very fine hair on my forearms I use that as a test (I have very thin Irish brown hair)

 

[whirlwynds]

I should clarify. One of the traditional japanese tests of sharpness is to hold the knife in your hand and reach behind your head and touch the blade to the hair on the back of your head. I believe they are testing the grabiness of the edge against the hair follicle or even cutting hair. I had a video link but cant find it now.

I am just wondering if anyone else does this any why.

 

[HumbleHomeCook]

If you're testing a knife edge against your hair follicles, well...

 

[stringer]

I should clarify. One of the traditional japanese tests of sharpness is to hold the knife in your hand and reach behind your head and touch the blade to the hair on the back of your head. I believe they are testing the grabiness of the edge against the hair follicle or even cutting hair. I had a video link but cant find it now.

I am just wondering if anyone else does this any why.

I don't do this with knives. But I do test my straight razors by feeling how it goes through a semi-taut belly button hair. Your fingertips are incredibly sensitive instruments. The Japanese guys are feeling the knife go through the hair by the vibrations that travel up the hair to their fingertips. Over time with practice you can tell if the edge is "there" or not. They use the hairs on the back of their head because if they used the hairs on the front of their heads their wives and mother in laws would yell at them.

It doesn't matter what sharpness test you use. All manner of paper products, body appendages, and whatever hairs happen to grow well enough on your body that you can afford to waste them will all work fine. Or just cut some onions and tomatoes.

 

[HumbleHomeCook]

Okay, I'll be serious and piggy back on @stringer's thoughts...

I've done all manner of "edge testing" to include the hair on the back of the head thing. Most of it, for me, if I'm being truly honest with myself, is novelty. My knives are all different and I sharpen many of them differently so there is not a real one-size-fits-all test.

In general, shaving arm hair, fingernail catch and cleanly cross-cutting receipt paper are my defaults but really, as @stringer said, it is my finger tips that tell me the most. I can cut paper towels, free slice a tomato, shave my calf bare, or all other manner of edge cutting curiosity but I ALWAYS feel the edge. And I feel it in various ways and different angles and such. I reckon combined with some cutting tests and actual performance has helped calibrate my touch to some degree. I know when it just isn't quite right. I can try to fool myself. I can impress myself with how it slid through whatever but my fingers generally know.

I use the arm hair and receipt paper for process feedback but ultimately it's how they perform that matter.

 

[stringer]

This guy covers the bases pretty well. There are other very sensitive body parts that work well besides fingertips. Like your tongue.

 

[whirlwynds]

Wow. Tongue test. Haven't tried that yet. Especially with abrasive grit, metal shavings and compound on the edge. Wonder what 1/2 micron compound tastes like!

 

[HumbleHomeCook]

Wow. Tongue test. Haven't tried that yet. Especially with abrasive grit, metal shavings and compound on the edge. Wonder what 1/2 micron compound tastes like!