Types of rectangular sharpening stones and how to use them

Widely used for the care of cutlery and other tools, rectangular sharpening stones are used in a variety of places, from industrial use to general household use. The rectangular-shaped square whetstone has been called a grindstone for a long time, and this article will explain its structure, uses, and applications.

What is a rectangular sharpening stone?

A rectangular sharpening stone is generally called a grindstone and is widely used. There are two types of artificially created rectangular sharpening stones: artificial grinding stones that are molded and fired using artificial abrasives as the main raw material, and natural grinding stones made from natural materials. There are three types of grindstones by use: coarse-grit grindstones for repairing chipped blades of kitchen knives, medium-grit grindstones for finishing stainless steel kitchen knives, and fine-grit grindstones for increasing the durability of kitchen knives and maintaining sharpness for a long time. Please use them according to your purpose.

Structure of a rectangular sharpening stone

A grindstone is composed of ‘abrasive grains’, ‘base material’, and ‘air bubbles’. In natural abrasive stones, the abrasive grains are fossilized microorganisms, and the base material is the clay that hardens the grains. Artificial grindstones are made by scientifically analyzing natural grindstones and hardening abrasive grains, which serve as the abrasive material, with bonding materials such as artificial resins and ceramics. When a blade is sharpened with a grindstone, the abrasive grains in the base material become the abrasive element, and the abrasive grains and base material of the grindstone itself are sharpened. With further sharpening, both the abrasive grains remaining in the base metal and the abrasive grains and base metal that have been sharpened effectively sharpen the blade. Since most grinding stone mines are now closed, natural grinding stones are extremely valuable. For this reason, artificial grindstones are commonly and widely used when talking about grinding stones.

Uses of rectangular sharpening stones

There are three main types of grindstones: coarse-grit grindstones, medium-grit grindstones and fine-grit grindstones. This is divided by grain size, and the grain size is divided by the size of the ‘abrasive grain’ contained in the grindstone, and each should be used properly according to the process. In the JIS standard, the grain size is indicated by a number starting with ‘#’, with smaller numbers indicating larger and rougher grains and larger numbers indicating smaller and finer grains. The smaller the number, the larger and rougher the grain.

Coarse-grit grindstones (#80~#400)

It is used when the blade is chipped or for repairing the blade. Do not use it for regular knife sharpening.

Medium-grit grindstones (#700~#1000)

It is used when the sharpness of the blade has deteriorated. This medium-grit grindstone is sufficient for daily use. After using a coarse-grit grindstone, use it to remove scratches and polish to finish the work.

Fine-grit grindstones (#3000~#8000)

Used by professional chefs to further sharpen the edge of the blade. It is not often used in the home.

How to use a rectangular sharpening stone

First, soak the artificial grindstone in water to soak it thoroughly. Fill a tub or other container with water in advance and soak the stone for 10 to 20 minutes. Bubbles will appear at first, but will stop after a while. When the bubbles stop, the grindstone is sufficiently hydrated, and you can start using it. The most important thing when sharpening knives is to keep the angle of the blade in contact with the grindstone constant. The grindstone should be positioned a little below the elbow, around the navel, and placed on a special stand or wet cloth. Hold the knife by the handle with your dominant hand, and secure the peak of the back of the knife blade and the jaw of the blade near the handle with your index finger and thumb to stabilize it.

After holding the knife, place it on the grindstone with the blade part toward you. Place the index and middle fingers of your non-dominant hand lightly on the blade to be sharpened and move it back and forth at an angle of about 45 degrees to the grindstone without exerting much force. As you sharpen the blade, the water will turn black, but do not pour it out, as the sharpening liquid will assist in sharpening the blade and further progress the sharpening of the knife. As the blade is sharpened, a burr will form on the edge of the blade, which can be seen by touching it with your hand. When the entire blade from the cutting edge to the chin of the knife is sharpened, sharpen the other side of the knife once or twice to remove the burr. This is the end of sharpening a knife using a grindstone. Then, try cutting a piece of newspaper with the knife, and if it cuts smoothly without getting stuck, you are done.

How to care for grindstones

When you sharpen knives and other blades, the grindstone itself is also sharpened, so it will inevitably become dented. If you sharpen a knife with a dented grindstone, you will not be able to get an accurate edge, so after using the grindstone, be sure to sharpen it until it is flattened using a surface straightener. If the blade is dented, the dented area will become black, so sharpen the blade until the blackened area is gone. Drain off the water thoroughly and store it in a shady, dry place.

You can use the knife for a long time by using the right grindstone that suits the purpose. Please use the right grindstone for the right purpose and take good care of your knives and other tools. Also, please do not forget to take care of the grindstone you use.