Surface Polish
This section discusses the surface polish of a katana and what grit abrasives
are used. The surface polish of a katana is as important to cutting as the geometry.
It is especially important for the durability of the edge and surface friction
of the blade. An edge from a coarse grit stone may feel very sharp and cut
well for the first few times, but it will quickly become dull. A rough finish
will also bind up in the target. Polishing and sharpening a katana are the
same process. For swords that will see real use, a full cosmetic polish is
not needed. Who wants to pay $2000 every year to keep your sword sharp.
A sharpening polish leaves some scratches on the surface and skips the purely
cosmetic steps.
The first thing everyone asks is what grit stones are used to polish or
sharpen a sword. What could be easier than selecting an abrasive? Is
that US, European, English, or Japanese grit? Are you specifying the mesh
used to separate the particles or the particle size. Everyone uses a
different standard and they don't compare well. Here is the results of my
research into grit.
Equivalent Grit Table
Particle
Size
(Microns) |
US
Grit |
Japanese
Grit |
Examples |
| 0.5 |
12000 |
25000 |
Chromium Oxide Polishing Compound, Moor
White Ceramic |
| 1 |
5000 |
10000 |
Honyama Awasi (Brown Stone), Linde C
Compound (Aluminum Oxide Powder) |
| 2 |
3000 |
6000 |
Karasu (Blue Stone), Awasi Toshi |
| 3 |
2000 |
4000 |
Uchigumori, Extra Fine White Ceramic, Green
Chrome Rouge, Spyderco Extra Fine Ceramic |
| 6 |
1200 |
2500 |
Ao-To (Blue Stone), Spyderco Fine Ceramic |
| 10 |
1000 |
2000 |
Hard Black Arkansas, Extra-Fine Diamond
Hone, Lansky Ultra-Fine Hone |
| 15 |
800 |
1500 |
Koma-Nagura, Hard White Arkansas, Extra Fine
Diamond, Medium Ceramic, Moor Black Ceramic |
| 20 |
600 |
1000 |
Soft Arkansas, Lansky Fine Hone, Ultra Fine
Scotch-Brite Pad, Spyderco Medium Ceramic |
| 25 |
480 |
800 |
Chu-Nagura, Washita Stone, Fine
Diamond |
| 35 |
320 |
500 |
Kaisei (Natural Sandstone), Fine India,
Medium Diamond, Super/Extra Fine Scotch-Brite
Belt/Pad |
| 45 |
280 |
400 |
Medium India, Fine Crystolon (Silicon
Carbide), Coarse Diamond, Lansky Medium Hone |
| 60 |
220 |
300 |
Binsui Coarse Stone, Extra Coarse Diamond
Hone, Very Fine Scotch-Brite Belt/Pad |
| 80 |
180 |
260 |
Fine Scotch-Brite Belt/Pad |
| 90 |
150 |
220 |
Medium Crystolon (Silicon Carbide), Coarse
India, Medium Scotch-Brite Belt/Pad |
| 110 |
120 |
180 |
Arato (Natural Sandstone Or Carborundum),
Lansky Course Hone |
| 150 |
100 |
150 |
Coarse Crystolon (Silicon Carbide) |
| 180 |
80 |
90 |
Lansky Extra Coarse Hone, Coarse Scotch-Brite
Belt/Pad |
If a sword just needs to be touched up, we use six progressively finer grits
from 800 to 12000 (Japanese). The polished surface is degraded if the edge
is touched up with anything coarser.
Japanese water stones are either natural and artificial. Natural stones
can be quite expensive, but artificial stones can be used for sharpening polish.
About half the stone used in a full cosmetic polish can also be artificial, but
some steps require specific natural stones. Artificial stones use a graded
abrasive suspended in either a clay or ceramic media. The stones use water
as a lubricant. A series of stones ranging from about 800 to 12000 grit
are used to sharpen blades in good shape. If a blade is badly shaped or
has chips to remove, stones down to 80 grit can be used. Water stones
should be soaked for 15 minutes before use. Mixing baking soda in the
water will help reduce corrosion of the blade during sharpening.
|