First Stones:
The first sharpening stones were “found” rocks. By trial and error, our ancestors determined what rocks were best and later identified where to find more. Then these sources were formally mined, and the rocks that later became known as stones were cut from the earth. Man-made stones began to appear as the demand for natural stones began to outstrip supply and because we thought we could make them better. However, we so liked our natural stones that we made the man-made stones to emulate natural stones.
All stones require a lubricant (either water or oil) to float the swarf (metal filings) away from the surface. In terms of cost, the higher the grit, the more the stone will cost.
Natural Stones:
Arkansas Stone or Novaculite
Novaculite is a hard, dense sedimentary rock composed of micro crystalline quartz. Novaculite stones are mined from veins in the Ouachita Mountains in Arkansas, hence the name, and come in a variety of grit ranges. Arkansas Stones are very dense, hard and wear very slowly. Flattening or keeping one flat is a once-in-awhile task, rather than prior to every use. Arkansas stones are primarily associated with a group of stones known as oilstones, although they may also be used with water. The oil or water is used to keep the surface of the stone clean while sharpening by floating away the swarf created by the removal of metal. Grits range from about 350 on the coarse end to above 900 up to 1200+ for a translucent or surgical black.
Natural Waterstones
The natural waterstones that we are perhaps most familiar with originate in Japan. They are as a group porous, soft and dish easily; therefore, they require frequent flattening. Water is used to keep the surface of the stone clean and swarf-free during sharpening. These stones are also cut from veins and vary in density and abrasive grain size. This variance can be combined in one stone having both coarse and fine sections. It was thought most of the veins for natural stones were depleted, which caused these stones to be very expensive. However, new veins have been discovered that are increasing the availability and lowering the prices. Grits range from coarse to extra fine
Man-Made Stones:
Oilstones
The two stones predominantly associated with this term are made with either Aluminum Oxide or Silicon Carbide – the former AO stones being orange to dark gray and the latter SiC stones being brown to dark gray. Oil is used to keep the surface of the oilstone free of swarf during the sharpening process. These stones are cast into shape and fired or baked in ovens. They are very hard and durable but somewhat limited in the range of grit size offered, usually being from about 100 for a coarse SiC stone to about 600 grit for a fine AO stone.
Waterstones/Ceramic Stones
These man-made stones are cast into shapes and fired or baked in ovens. They can range from soft/porous like natural waterstones to semi-soft/porous to hard and not porous at all. The stones use water to float the swarf away and keep the surface of the stone clean during sharpening. These stones require flattening, usually before each use. Grits range from 120 grit to (in one brand) 30,000 grit.
Diamond Stones:
Diamond Stones are generally metal plates upon which a coating of diamonds has been applied. They can be used dry or with water to float away the swarf, come flat within the manufacturer’s tolerance (may vary), and do not require flattening – ever. Diamonds have a reputation for durability, but they will eventually wear out. Grits range runs from 120 to 8000.
