Woodworker's Journal 1993-17-4, страница 23

Arkansas stones have been used for well over a century, and are still the favorite of many veteran sharpeners today. These natural stones are used to put the final cutting edge on a tool after grinding on a wheel or initial shaping with a coarser synthetic stone.

These stones fall into the oil stone category because you need to coat the stone with a thin oil lubricant to help "float" metal particles off the stone surface while sharpening. Some woodworkers initially soak the stone in an oil bath until it is completely saturated, and then add the oil as needed during use. (You can also use water as a lubricant, but it's generally not as effective). The oil keeps ihe stone from clogging or glazing, and is also used to clean off the stone after you're done. Most woodworking catalogs carry commercial honing or sharpening oils, although some experts claim that ordinary mineral oil or household (sewing machine) oil works just as well. The secret to keeping the stone clean and free-cutting is to use plenty of oil and w ipe off the stone frequently to remove accumulated metal particles. Bccausc Arkansas stones use an oil lubricant, some woodworkers (especially carvers) shy away from them. The feeling is any oil residue left on the cutting edge can contaminate their projects.

While the colors of Arkansas stones range from black to white, all contain a natural mineral abrasive called novaculite (a form of quart/1. The size and density of the abrasive particles determines the stone's coarseness, as well as it's hardness. Soft, coarse stones contain large, loosely bonded abrasive particles, so they cut faster than harder stones; they also wear oui or dish more quickly.

These stones range from 35(1 grii to 40(1 grit. However, because the stones are of natural origin, the particle sizes aren't nearly as uniform as those in synthetic stones. For ihis reason. Arkansas slones usually aren't classified by grit size, but by hardness, as follows: Washita (coarse), soft Arkansas (medium). Hard white or gray Arkansas (medium/fine) and hard black Arkansas (fine). Approximate grit sizes are listed in the chart on pace 2ft. Many sharpeners contend thai a hard black Arkansas stone produces the finest cutting edge of all stones, natural or synthetic.

Due to their dense structure. Arkansas stones cut more slow ly than waterstones of (lie same grit, but they also tend to last longer. They're moderately expensive as stones go, and will probably become more so in the future. Hard black Arkansas stones, especially, are becoming increasingly rare (ergo expensive), so if you want one. you'd better buy it soon.

Because the size and density of (he abrasive particles aren't as consistent as they are in man-made stones, each indiv idual stone in any given "grit" has a slightly uneven cutting action. However, you can now buy manufactured "perfect" Arkansas

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stones. These stones are made by pulverizing natural Arkansas stones, screening and grading the natural abrasive particles by grit size, then rebonding them to form a stone that is "perfect" in grain size, shape, and density. According to some users, these stones have a faster, more uniform cutting action than natural stones.

Synthetic Oil Stones (India and Crystolon)

These stones are made of bonded aluminum oxide or silicon carbide—the same man-made abrasives used in sandpaper and grinding wheels. In woodworking catalogs, you'll see most aluminum oxide stones referred to as India stones; silicon carbide stones are called Crvstolon or carborundum stones. (India and Crystolon are trade names of the Norton Company.

although "India" has somewhat fallen into generic use over the years.)

India and Crystolon oil slones generally cut faster and more uniformly than natural Arkansas stones, and have the same wear characteristics. They're also less expensive. Both India and Crystolon slones come in "coarse." "medium," and "fine" grit designations. Coarse stones may take the place of a power grinder for fast metal removal, such as when establishing a bevel or removing large nicks in the culling edge. Medium and fine stones are used prior to sharpening with white/black Arkansas stones (500-900 U.S. grit), medium and fine waterstones (2000 or higher Japanese grit), fine diamond, or fine ceramic stones.

Many old-timers prefer natural Arkansas stones f.f stones at left). Stones at right are man-made versions, railed "perfect" Arkansas stones.

Man made India (aluminum oxide) slones come in many shapes for a variety of sharpening jobs. They're available in coarser grits only.