The Norton Crystolon 100/280-grit combination abrasive machine knife stone is made of silicon carbide with 100 grit on one face for repairing cutting edges and 280 grit on the opposite face for sharpening and maintaining them; it sharpens to moderate tolerances when it is more important to sharpen the blade quickly than to produce a fine cutting edge. This disk-shaped hand oilstone is commonly used to restore cutting edges on paper- and cloth-cutting knives and planer knives while they are on the machine; it can also be a preferred stone for garden and household tools. A groove around the circumference of the stone offers a secure hold and protection for fingers. Its compactness makes it easily portable. This silicon carbide stone must be lubricated with oil before use, to prevent metal from bonding with the abrasive surface of the stone. The stone is fast-cutting and offers effective sharpening even under light pressure. It is created by grading silicon carbide to a consistent particle size and blending it with bonding agents. It is then molded and surface-finished. This knife stone is 1-1/2 inches high and 4 inches in diameter, suitable for hand use. It conforms to the American National Standards Institute (ANSI) abrasive grit standard. Sharpening stones, or whetstones, are abrasive surfaces used to sharpen and hone the edges of steel cutting implements, such as chisels, knives, scissors, hand scrapers, and plane blades. Sharpening is the process of creating or re-establishing a cutting edge by grinding away portions of the metal to adjust the angle of the edge and reform the shape. Honing removes small imperfections. Stones can be flat, for working flat edges, or shaped, for edges that are more complex. Sharpening stones are made of natural or synthetic materials that range from softer to harder, and are categorized by the size of their abrasive particles, known as grit. A stone with a coarser grit is used when more metal needs to be removed (e.g., when sharpening a nicked or very dull blade); the stone with the finest grit produces the sharpest edge. Where numbers are assigned to specify grit, they range from coarser grit (low) to finer grit (high). Some sharpening stones are designed for use with a lubricating liquid, some can be used dry, and others can be used either wet or dry. When used with lubricating liquid, a sharpening stone can be called a waterstone or an oilstone, based on the lubricant required. Norton Abrasives manufactures sanding, grinding, and polishing abrasives, and has been located in the United States since 1885. Norton, now a brand of Saint-Gobain, meets ISO 9000 and 14001 certification for quality and environmental management standards.