Process of Polishing a Tanto Blade

After the blade is hardened and tempered, the final geometry is created and the surface smoothed and polished with various abrasive stones. Polishing is broken into two distinct stages, the rough polish occurring before the fittings and scabbard are made, and the final polish once the rest of the knife is complete.

A combination of Japanese waterstones, both synthetic and natural, and diamond stones 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.


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 blade is much harder than is 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 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, similar to the method of using a sen to set the pre-quench geometry after forging.

Island Blacksmith: Hand forged reclaimed tanto made with traditional techniques
A portable bench for rough polishing after the hardening process of yaki-ire. Coarse stones may be used dry or wet.
Island Blacksmith: Hand forged reclaimed tanto made with traditional techniques
After yaki-ire and yaki-modoshi, a test with a Sun Tiger (朝日虎印) #80 grit or #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.
Island Blacksmith: Hand forged reclaimed tanto made with traditional techniques
A Sun Tiger #80 grit waterstone is used to remove the bulk of the material at the edge and 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.
Island Blacksmith: Hand forged reclaimed tanto made with traditional techniques
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.
Island Blacksmith: Hand forged reclaimed tanto made with traditional techniques
This is the official “coarse” stage of the polish, working perpendicular to the blade with a #180 grit waterstone (220mesh/60micron/extra-coarse DMT diamond stone shown, not recommended due to deep gouging on the ji) until all the diagonal lines of the rough shaping are erased and the edge is almost “sharp”. This is also the first stone to touch the mune (spine) since the drawfiling that was done before yaki-ire.
Island Blacksmith: Hand forged reclaimed tanto made with traditional techniques
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.
Island Blacksmith: Hand forged yoroidoshi tanto in shirasaya, made from reclaimed and natural materials using traditional techniques
A #300 grit waterstone is next, 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.

Before the rest of the polish, the habaki, seppa, and other fittings are created. See the interim steps here:
Making Habaki (Blade Collar) | Making Tsuka (Handle) |
Making Saya (Scabbard)


Final Polish (Togi)

Once the fittings and scabbard are complete, the blade is given its final polish. Depending on the condition of the blade, the last used stone (#300, #500, or #700) is 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 last steps are carried out with natural 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 (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. The blade is carefully cleaned and oiled frequently with a clove oil blend for the first few days and weeks after polishing.

Island Blacksmith: Hand forged yoroidoshi tanto in shirasaya, made from reclaimed and natural materials using traditional techniques
A new stone must be flattened and shaped with a diamond stone or other coarse stone to remove saw marks before use.
Island Blacksmith: Hand forged yoroidoshi tanto in shirasaya, made from reclaimed and natural materials using traditional techniques
Beginning with the natural binsui-do to remove the last of the arato/kongo-do stone scratches. This is the last stone to make changes in refining the shape.
Island Blacksmith: Hand forged yoroidoshi tanto in shirasaya, made from reclaimed and natural materials using traditional techniques
Natural kaisei-do is used steeply diagonally or almost lengthwise to remove the binsui scratches.
Island Blacksmith: Hand forged yoroidoshi tanto in shirasaya, made from reclaimed and natural materials using traditional techniques
Chu-nagura-do more clearly defining the hamon. From this stone onward the scratch direction is always lengthwise.
Island Blacksmith: Hand forged yoroidoshi tanto in shirasaya, made from reclaimed and natural materials using traditional techniques
A white komanagura-do increases the polish level of the ha noticeably.
Island Blacksmith: Hand forged yoroidoshi tanto in shirasaya, made from reclaimed and natural materials using traditional techniques
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.
Island Blacksmith: Hand forged yoroidoshi tanto in shirasaya, made from reclaimed and natural materials using traditional techniques
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.
Island Blacksmith: Hand forged yoroidoshi tanto in shirasaya, made from reclaimed and natural materials using traditional techniques
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 up the surface and add depth. This stage is very time consuming as well.
Island Blacksmith: Hand forged yoroidoshi tanto in shirasaya, made from reclaimed and natural materials using traditional techniques
Boiling water is poured over the steel to heat it up. The water is quickly dried off and sashikomi nugui made from satetsu (iron sand) and clove oil is applied.
Island Blacksmith: Hand forged yoroidoshi tanto in shirasaya, made from reclaimed and natural materials using traditional techniques
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.
Island Blacksmith: Hand forged yoroidoshi tanto in shirasaya, made from reclaimed and natural materials using traditional techniques
The hamon is clearly visible along with some of the artifacts in the steel, particularly in the ji.
Island Blacksmith: Hand forged tanto, made from reclaimed and natural materials using traditional techniques
Careful observation in the correct lighting conditions may reveal some interesting details of the hamon that are usually hidden.