The main goal of polishing a sword is to restore/finish a blade by removing the least amount of material as possible while still maintaining the shape the smith had intended. It is very important to bring out the best a blade has to offer without sacrificing the safety of a blade by cutting corners to bring out its activities.
Here is a quick overview on how to polish a sword. You may think that by reading books, websites, buying some stones or attending sword shows talking with other aficionados would make you an expert or traditional polishers. There are more aspects involved in polishing than that. Traditional Japanese sword polishing is a tedious process requiring skills, patience, knowledge, control and a lot more. Provided that you are genuinely interested in learning this craft, look for a professional or experienced teacher who will work with you in person. If you need to have your sword blade polished, make sure you are sending it to a reputable polisher who will do good rather than harm on your sword.
Shitaji as the Foundation Polish
When Japanese blade is polished, it calls for the most important aspect of polishing called Shitaji. The foundation polish of a blade plays a critical role thus it should be done properly form the beginning to achieve a good overall polish. Contrary to the popular belief that polishing is a process of removing scratches until the hamon on a blade is visible, this isn’t so true.
There’s a lot more to traditional polishing than bringing out the activities of a blade. The polishing of blades demands adjustment to maximize the full potential of the finished product, despite the kind of blade you’re going to work on or how much a particular smith prepared the blade for polishing. The standard fare includes the geometry and symmetry of the blade, checking or fixing the niku, wobbles on the surface, crispness of the shinogi-ji and mune among others. Every single blade must be tweaked in some way to correct its symmetry and geometry but not to the extent of risking the shape and trademark of the blade.
Take a look to sets of Japanese polishing stones in either synthetic or natural forms.
Kongo-do is most often used to make drastic adjustments to the geometry of the blade. It removes heavy rust pits and chips on the blade. Extra care should be given upon using this stone as it easily ruins a blade if used improperly. Don’t use this stone on new swords in binsui-do finish or blades straight out of the heat treat.
To primarily define a blade’s geometry, use a binsui-do stone. This is one of the stones compatible to set a blade’s geometry and to prime an ample definition. What’s more is it refines the scratches of the previous stone.
Kasei-do is a follow-up stone to eliminate the scratches left by Binsui-do stone. This is a final stone for setting and defining the geometry. When this stone is used as a foundation stone, it is a must to constantly check the blade’s geometry to ensure that all lines are kept straight, sharp and symmetrical. Even a single stroke can remove too much material, gouge the blade leading to wobbles and various accidents which in turn damaging your blade. Once the blade is damaged, the stone is defeating its purpose of redefining the result of the previous stone.
Nagua-do is the stone to remove the scratches made by Kaisai-do stone. Nagura-do primarily acts as a scratch remover although the geometry of the blade is always maintained and checked. The geometry of the blade is a high priority that an incorrect geometry will make the blade look carelessly polished.
Komanagura-do stone is very soft and fine. It is used to remove or refine the scratches of the Chunagura stone and prepares the blade for Uchigumori Stage.
Igumori Hado is another fine and soft stone used on the Ha (hardened edge) to define the hamon as well as bring out any hararaki on the yakiba.
Uchigumori Jido is much finer and usually a little harder stone than the Hado. Jido is used to bring out the Jihada (grain pattern) of the blade.
Perhaps the most difficult stones to master are the last two stones. These stones ask for a higher cost since they are only available in natural form. It involves a lot of patience and skill to use these stones properly. The worst result would scratch a blade easily and render many hours of work to waste due to improper use. Once the blade has shown scratches then you need to take your blade back again for additional polishing work. It is best to have a collection of all necessary stones to match the right one that suits a particular blade although it could be quite expensive.
Shiage - Finishing Polish
Tsuya or finger stone work
This process is where a piece of uchigumori stone is backed with tanned yoshino-gami lacquered and sized to fit underneath my thumb. The stone is as thin as a paper in width and rubbed on the blade with tojiru or polishing paste. The polishing paste is made by rubbing 2 uchigumori stones together.
Haruya are thinned pieces from uchigumori koppa. Its function is to polish the yakiba (hardened edge) of the blade. The habuchi will stand out from the more white and milky look given by the yakiba.
Nugui is the final process of making everything stands out on the blade more specifically the hamon, jihada and any other hataraki which is present on the blade. A proper nugui mixture could make a big difference in the blade’s final look. You can use jitekko, aoko, uchiko, akako, etc. or a combination of powders to make my nugui. The choice of stones, of course, depends on the type of blade and the contrast you want to achieve with your blade. Be aware that some steels are not compatible with nugui due to its vanadium and carbide content. A traditional or hybrid method works best with blades of modern day steel for a more traditional look.
Migaki-Togi is the process of burnishing the Shinogiji and the Mune in order to transform the blade to a high mirror shine. There are three different kinds of burnishing rods in 2 stages namely Shitamigaki (Foundation Burnishing) and Uemegaki (finishing Burnishing). Ibota powder is used so that my migakibo will slide on top of the steel and burnish the surface to a mirror shine.
Sugikiri or Defining the Yokote
Sugikiri is a process where apiece of hazuya to polish out the tip on a shinogi zukuri blade at a 90-degree angle. This gives the kissaki part a more whitish look than the rest of the blade and also brings out the boshi.
Narume - Polishing of the Hakissaki
Narume is the final stage of polishing the hakisaki where a bigger piece of thinned hazuya is placed on top of narume-dai. This is the stage that renders the ha-kissaki to a scratch free finish.
Nagashi - Polisher’s Signature
Most polishers in Japan will put their nagashi on a blade upon completion signifying the school. The lines appear as a series of 7 to 13 lines underneath the habaki on the shinogiji. Sometimes there are also 3 lines on each side of the mune towards the tip area of the blade.