Jnat Kawa - The Skin

Karasu Kawa

 Some Thoughts and Facts about Kawa

Kawa is that hard-as-hell layer on the bottom of many Jnats. This skin can also be seen on the sides, and occasionally on the top of the stone too.  

 Kawa is usually very hard; hard enough to generate sparks with a belt sander.  It’s a layer of sediment that is fixed onto the stone. Most often, it appears to be laden with Iron oxide, and I believe that the skin itself is a form of chert. 

The history and science about the formation of Jnats is fantastic. But – there’s a certain reality that we need to deal with here. Skin, or Kawa, can easily ruin honing or sharpening efforts. It’s a very hard and scratchy substance that is toxic to a refined edge. It might be considered toxic to your health also - losing an hour or two of hard work because a flake of skin got into the Tomo slurry will definitely raise one’s blood pressure. 

Many people prefer a stone to have the bottom of the stone covered in Kawa. Some collectors and enthusiasts consider skin to be an indicator of the stone’s origin. Whether or not that’s true is irrelevant, factually – some collectors insist on only purchasing stones that have a good amount of Kawa visible. Equally important, some very high-end stones do not have skin showing on any sides. 

 Occasionally – a stone will have skin on the top, or running through the middle of it. The latter is extremely problematic. This type of situation relegates the stone to being tossed out as junk. Sometimes, they can be cut up into Tomo Nagura. Skin on the stone’s top can usually be lapped off but it will mean losing a tremendous amount of stone in the process. 

Skin on the bottom of the stone is never a problem. Skin on the sides can be a challenge in that the chamfer at the edge might need to be larger to clear the skin out of the way. 

It’s important to not confuse Suji, which are non-toxic hairlines in the stone, with skin though. Suji are innocuous and some consider those lines to be beautiful. Ke-Suji are toxic lines, they could be a seam of skin or, more usually, it’s another type of toxic inclusion. 

The presence, or lack of, Skin, or Kawa, provides a lot of fodder for conversation and debate amongst sellers, collectors and those who study stones at very deep levels. Quite often, there are heated debates about its relevance and importance. 

My own experience - I was once looking at two Shobu Awase side-by-side, identical in just about every way including shape, size and weight; one had skin, the other did not. The one without skin was about 25% less expensive. I asked the seller why and he replied – ‘no skin!’. I laughed and bought the one without skin. I don’t hone on skin, or stamps for that matter. I liked that stone a lot, so a week later I went back and bought the one with skin too. 

For the majority of Jnat users, Kawa is just another facet of the stone being created and formed by nature. The skin can be problematic, or just some hard stuff in an out-of-the-way place that may or may not enhance the stone’s resale value.


© Keith V Johnson 2014 - 2018