After the blade is hardened and tempered, the final geometry is created and the surface smoothed and polished with various abrasive stones. In contrast to other methods, stone polished blades have a different surface look and retain their crisp edges and lines. Polishing is broken into three distinct stages, the rough polish occurring before the fittings and scabbard are made, and the foundation polish and final polish once the rest of the knife is complete.
The word togi (研ぎ) does not differentiate between the action of polishing and the action of sharpening, for a Japanese sword the operations are one and the same, an integral process. A combination of Japanese waterstones, both synthetic and natural, are used to remove smaller and smaller amounts of steel and give the knife its final shape and surface. Each stone is progressively finer and is used with a different orientation so that the scratches from the previous stones may be clearly seen. Once they are erased, the next stone can be used, each time refining the geometry and surfaces towards the final goal. Once the rough polish is finished, work on the blade is halted until after the habaki, seppa, tsuka, and saya are created and fitted. This prevents accidental scratches while working on other parts of the knife.
A series of coarse synthetic and fine natural waterstones from Japan are used to refine and polish blades.
Rough Polish (Kaji-Togi)
At this stage, the large volume of steel left around the edge for the process of yaki-ire must be removed, and the blade and tang are given their final geometry. The edge of the blade is much harder than it was during the rough shaping stage and steel cannot be removed with any metal tools. A combination of natural and artificial waterstones are necessary for this process.
Care is taken to refine each part of the blade geometry and bring the planes into proper alignment and proportion beginning with coarse stones and quicker removal and ending with very fine stones and subtle adjustments. Tagane-ha (chisel edge) is a common technique for first establishing the centre line of the edge. Both sides of the edge are honed away on a 45 degree angle and then the excess material in between the edge and the spine is removed in sections, similar to the method of using a sen to set the pre-quench geometry after forging.
Using a vise to straighten a blade as much as possible before polishing. Copper rods provide non-marring pressure points. Hammer straightening on a stump is another method used at the very first stages.
A simple dry working station for coarse stones using a board with a hook over the edge of a stump. Coarse stones may be used dry and the powder saved for use in the yaki-ire clay mixture.
A portable bench for rough polishing after the hardening process of yaki-ire. Water can also be used with this set up.
After yaki-ire and yaki-modoshi, a test with a Sun Tiger (朝日虎印) #80 grit or Lobster Carbon #120 grit Japanese waterstone to check the hamon placement before proceeding, the edge is still 1-2mm thick and yaki-ire can be repeated to adjust the hamon or the sori if necessary.
A Sun Tiger #80 grit waterstone is used to remove the bulk of the material at the edge, bring the blade very close to the finished geometry, and correct any major issues. During this stage the straightening block may also be revisited to make adjustments to the symmetry and preserve as much steel as possible.
A #120 grit waterstone is used to clean up the deep scratches from the #80 grit and remove material from the edge until it is less than 1/4mm thick. Frequent careful checking ensures that any irregularities are corrected while there is still extra steel to work with.
This is the official “coarse” stage of the polish, working perpendicular to the blade with a #180 grit waterstone until all the diagonal lines of the rough shaping are erased and the edge is almost at its final geometry. This is also usually the first stone to touch the mune (spine) since the drawfiling that was done before yaki-ire.
Moving to a #220grit waterstone and working diagonally until the perpendicular scratches are erased. The polished area should extend along the tang to include the area that will sit under the habaki. This stone brings the edge right to zero thickness (but not quite “sharp”).
A #300 grit Monotaro waterstone is next, and may be followed by a #500 and possibly a #700, each used on a different angle to ensure scratches are removed. One of these three stones will be the last for kaji-togi.
Kaji-togi is often done at least partially in a different location, with a different polishing platform, or with a cover over the platform surface in order to prevent contamination scratches from the coarse grit stones during later stages.
Once the fittings and scabbard are complete, the blade is first given the rest of its foundation polish and then the final polish. Depending on the condition of the blade, the last used stone (#300, #500, or #700) may be repeated again to check that there are no new scratches from the workshop and then finer and finer stones are used to complete the finish.
Most of the foundation polish is carried out with natural (or high-quality synthetic) Japanese waterstones which cause the hamon and other steel activity to show up against the body of the blade. A Japanese waterstone forms a slurry like fine clay with suspended particles in it, water (sometimes with a little baking soda to combat rust) is used to control its viscosity and how much stays on the stone during use. A natural stone gives a nice final finish with a unique look due to its slight variation of hardness and grit size.
A togi-dai (研ぎ台) polishing platform for collecting water and swarf during fine stages using waterstones.
A new stone must be flattened and shaped with a diamond stone or other coarse stone to remove saw marks and chamfer the edges before use.
Beginning with the natural #500/#700 to remove the last of the arato/kongo-do stone scratches.
The natural binsui-do is the last stone to make subtle changes in refining the shape of the blade.
A #1000 synthetic is used steeply diagonally or almost lengthwise to remove the scratches from this particular binsui.
Natural kaisei-do is used lengthwise or almost lengthwise to remove the #1000 scratches.
Chu-nagura-do more clearly defining the hamon. From this stone onward the scratch direction is always lengthwise.
A white komanagura-do increases the polish level of the ha noticeably.
Each successive stone is finer and progressively refines the geometry of the blade and smooths the surface.
Finishing Polish (Shiage Togi)
Depending on the steel and the desired look, the final stages may take almost as long as all the other stages together. An uchigumori stone is used to bring out all the internal aspects of the steel surface and then small finger stones are used to work over the entire surface again to remove scratches and give an even look. Finally sashikomi nugui made from satetsu (iron sand) and clove oil is applied to darken the surface and highlight the edge. Sashikomi (差し込み研ぎ) is an older style of polish that is known for its subtlety and honest view of the activity in the steel. The blade is carefully cleaned and oiled frequently with a clove oil blend for the first few days and weeks after polishing.
Suita uchigumori-do is used to bring out the final details of the steel, focusing more time and pressure in the area of the transition between ha and ji. Working with uchigumori-do is a very time and energy intensive stage.
Other types of uchigumori may be used depending on the steel and hardness, and various natural narutaki-do are optionally used to work on the ji area if necessary.
Hazuya and jizuya fingerstones made from flakes of uchigumori-do and narutaki-do koppa attached to washi paper with natural urushi are used to even the surface and add depth.
The fingerstone stage is very time consuming as well, each area of the surface must be carefully polished evenly, working on a few cm at a time.
The fingerstones are used to even out any remaining scuffs and unevenness left from the uchigumori stone.
Boiling water is poured over the steel to heat it up.
The water is quickly dried off and sashikomi nugui made from finely ground satetsu (iron sand) and clove oil is applied.
Soft cotton is used to rub in the sashikomi nugui and darken the ji area while it is hot. Excess is removed with washi paper.
The hamon is clearly visible along with some of the artifacts in the steel, particularly in the ji.
With the subtle sashikomi style polish, careful observation in the correct lighting conditions may reveal some interesting details of the hamon that are usually hidden.
