Oilstones are still favored by many for their hard, stay-flat-ness and general reduced maintenance. Oil helps prevent rust but it can interfere with some finishes; so, like water, it’s best contained. The oil of choice can be many things; there are brand-name honing oils, mineral oil, baby oil, 3-in-1, 20W, diesel oil, ATF, etc. I use light hydraulic oil because I happen to have a bucket of it and it works very well – clean, clear, odorless. Don’t use any oil that dries such as linseed oil. You’ll clog the pores of the stone irreparably. Adam Cherubini uses oil stones with a spray of soapy water instead of oil. He just grates some Ivory hand soap into a sprayer and adds water. The surfactant action of the soap keeps the steel particles in suspension in the water and he prefers the water to oil in his shop. He recommends cleaning the stones well first, even if they’ve been used with oil, by running them through the dishwasher (you might want to do this when your spouse is away) before switching from oil to soapy water.
Oilstones have become less popular over the years, and some natural grades have been nearly mined out, becoming quite rare. Traditionally they’ve been mined, in North America anyway, in the Ouachita Mountains near Hot Springs, Arkansas. They’re composed primarily of a form of silicon dioxide known as novaculite. The more common grit sizes of natural oilstones are called Washita, Soft-, and Hard Arkansas, Black Hard and Translucent. Manufactured oilstones are India (aluminum oxide grit) and Carborundum (silicon carbide grit). The silicon dioxide in novaculite is not as hard as aluminum oxide or silicon carbide; hence the slower cutting action of natural oilstones; the grit grains are worn dull and the cutting action slows.
Even though oilstones offer a hard surface that wears slowly, they do wear down and need flattening from time to time. A diamond plate works best for this and will flatten an oilstone efficiently, exposing new, sharp grit at the same time.
Oilstones cut more slowly, almost like they’re being more careful. I find sharpening on oilstones a bit meditative, the abrasive seeming to burnish and polish as much as cutting away the steel.
*Photo courtesy of Saint-Gobain Abrasives, Inc. 2008