Japanese sharpening stones
Japanese sharpening stones
EXPERT KNOWLEDGE JAPANESE SHARPENING STONES
Sharpening on Japanese waterstones
This method, equally suitable for Knives; Tools; Knives and tools; has the following advantages:
- Hardness and edge retention of the Steel are not affected as no heat is generated.
- Due to the wide range of Grits available, any desired fineness of edge can be achieved.
- In contrast to machine sharpening, a basic set of Grinding stones is affordable for every user.
Japanese sharpening stones are traditionally designed for use with water
The water serves as a rinsing medium here. It prevents the pores of the stone from becoming clogged by the abrasion and reduces its grinding effect. If the stone is rinsed less frequently with water, a pasty slurry forms from the abrasion, which reduces the grinding effect. This is utilised by experienced sharpeners to achieve a finer grinding effect and thus compensate for a larger grain size difference between Sharpening stones. Resin-bonded stones, such as King, must be stored in a water bath for 10-15 minutes before use. Ceramic-bonded stones, such as Shapton stones, hardly absorb any water. Wetting with water from a spray bottle is sufficient here.
Japanese sharpening stones differ in terms of the type of bond and also the type of abrasive.
Abrasives for Japanese sharpening stones
Grinding stones can basically be divided into two categories: natural stones and synthetic stones.
- Natural stones are, of course, naturally occurring stones that are extracted from a quarry.
- SyntheticSharpening stones are artificially produced from grinding granulate and bonding agents.
Natural sharpening stones
Natural sharpening stones are quarried in a quarry, cut to size, pre-ground and are ready for use from this point onwards.
In principle, you could sharpen with any stone found in nature. However, very few types of natural stone are both fine and hard enough to sharpen satisfactorily.
Examples of Japanese natural sharpening stones are
Honyama quarry stone (No.711303) Very fine stones from the Honyama site.
Japanese natural stone Aka (No.711534) Sand-lime stone with a medium Grit. Very open structure with high abrasive effect, from the Amakusa region.
Natural sharpening stones generally remove less material. This allows a controlled and precise sharpening result to be achieved. The sharpening process takes longer overall than with synthetic stones.
No two natural sharpening stones are the same. As the grain size of a stone cannot be precisely determined, a rough estimate of 6000 to 8000, for example, is often given.
Quarry in Honyama, Japan
Quarry stone "Honyama" (No.711303)
Japanese natural stone "Aka" (No.711534)
Synthetic Sharpening stones
The Grit of synthetic Grinding stones can be specified very precisely.
The starting point for synthetic Grinding stones is white, brown or grey aluminium oxide or silicon carbide in powder form. Abrasive silicon carbide is suitable for coarse grits due to its good removal rate, while aluminium oxide is used for finer grits.
Production of synthetic Sharpening stones
(very rough overview / each Manufacturer has its own recipe and technique)
The Abrasive is mixed with a binder and then pressed into the desired shape. The binder consists of natural products such as cellulose, wax, clay, magnesium or synthetic products such as synthetic resins.
The mixture is then fired in the Shape. The result is a hard Sharpening stone.
The different colours of the Sharpening stones usually come from dyes that are added by the Manufacturer to make it easier to distinguish the different Grits.
Dressing the Grinding stones
Many Japanese waterstones have a rather soft, open-pored bond, which constantly releases fresh abrasive particles during sharpening and thus enables a high level of effectiveness. The resulting wear requires regular dressing of the waterstones. The stones usually need to be soaked in water before use.
Ceramic sharpening stones (splash and go), on the other hand, have a very hard bond and little wear. It needs to be dressed less often. However, in order to achieve good sharpening performance, the Manufacturer must use very high-quality and wear-resistant abrasive particles. This is why such stones are usually more expensive.
In extreme cases where the bond of the abrasive particles is completely rigid and the stone is therefore virtually wear-free, diamonds are used as abrasive particles (DMT).
Grit
The Grit indicates the fineness of an Abrasive. In Europe, it is specified according to Fepa F for Grinding stones and Fepa P for Abrasive paper sandpaper (e.g. P 220) and is defined according to the number of meshes per square inch of a sieve. For example, a 500 Grit Abrasive will just pass through a screen with 500 meshes per square inch.
In some cases, often in the USA, the Grit is also described by specifying the size of the abrasive particles in microns (= 1/1000 mm). In Japan, the grit size is specified according to JIS (Japanese Industrial Standard). There are tables with which different specifications can be roughly compared.
Grit 80-220 is used for roughing (rough shaping, grinding out grooves or chipping), Grit 800-2000 for sharpening, Grit 3000-12 000 for honing and polishing.
Sharpening a knife on Japanese sharpening stones:
Freehand knife sharpening on Japanese sharpening stones is an art that requires patience and technique, but the results are worth it. The following procedure describes the essential steps:
- Preparing the Grinding Stone: first, the whetstone must either be soaked in water, for about 10-15 minutes, until no more air bubbles rise or, in the case of Ceramic sharpening stones, wetted with water. During sharpening, the stone should be kept moist by occasionally applying water.
- Determining the Grinding angle: The correct Angle is usually between 15 and 20 degrees. This Angle is crucial to achieve a precise cutting edge. Grinding aids can be used to keep the Angle constant.
- Sharpen with the coarse Grit (e.g. 1000): For blunt knives without visible damage, a coarse Grit is selected first. The knife is placed on the stone at an even Angle and drawn across the entire Length of the blade in even strokes. This process is repeated on both sides of the blade until a burr forms.
- Checking the burr: The burr along the cutting edge indicates that both sides have been sharpened evenly. As soon as the burr is clearly noticeable, you can move on to the next finer Grit.
- Sharpen with the medium Grit (e.g. 3000-6000): Others now use a medium Grit to further refine the sharpness. The same sharpening process as before is carried out, but with gentler movements and less pressure.
- Polishing with the fine Grit (e.g. 8000 and higher): A very fine Grinding stones is used for a particularly sharp edge. The sharpening process is repeated again to polish the blade and remove any remaining imperfections.
- Deburring: To remove the fine burr, the knife is lightly dragged across the stone at an Angle of about 15 degrees alternately. A leather honing belt with Polishing pastes can be used to polish the edge and remove the burr completely.
- Cleaning and sharpening test: After sharpening, the knife is thoroughly cleaned with water and dried. The sharpness can be checked by cutting tests, e.g. on paper or tomatoes. A well-sharpened blade cuts effortlessly and precisely.
In this way, a knife can be effectively sharpened on Japanese sharpening stones to achieve a long-lasting and extremely sharp edge.
Japanese sharpening stones produce an extremely fine and durable edge that is suitable for the highest demands. All in all, Japanese sharpening stones are an indispensable choice for anyone who values sharp and precise blades - whether in the trade, in the kitchen or outdoors.
