Sharpening is the process of creating or refining the edge joining two non-coplanar faces into a converging apex, thereby creating an edge of appropriate shape on a tool or implement designed for cutting. Sharpening is done by removing material on an implement with an abrasive substance harder than the material of the implement, followed sometimes by processes to polish/hone the sharp surface to increase smoothness. Tools and materials There are many ways of sharpening tools. Malleable metal surfaces such as bronze, iron and mild steel may be formed by beating or peening a flat surface into a sharp edge. This process also causes work hardening. An abrasive material may be rubbed against the cutting edge to be sharpened. The most traditional abrasive material is a natural stone such as sandstone or granite. Modern synthetic grinding wheels and flat sharpening stones can be manufactured in precise grades of abrasiveness according to the intended process. A sharp edge may be 'dressed' using a Honing steel The substance on the sharpening surface must be harder (hardness is measured on the Mohs scale) than the material being sharpened; diamond is extremely hard, making diamond dust very effective for sharpening, though expensive; less costly, but less hard, abrasives are available, such as synthetic and natural Japanese waterstones. Several cutlery manufacturers now offer electric knife sharpeners with multiple stages with at least one grinding stage. These electric sharpeners are typically used in the kitchen but have the ability to sharpen blades such as pocket or tactical knives. The main benefit of using an electric sharpener is speed with many models that can complete the sharpening process in one to two minutes. The disadvantage is that the sharpening angle is fixed so some specialized knives, like a Japanese style Santoku, may need additional attention to sharpen to the ideal angle. Angles Very sharp knives sharpen at about 10 dps (degrees per side) (which implies that the knife's edge has an included angle of 20-degrees). Generally speaking, razors, paring knives, and fillet knives should be the sharpest knives at an angle of 12° – 18°. Most kitchen knives, like utility/slicing knives, chef's knives, boning knives, carving knives, should be sharpened to 15° – 25°. The exceptions are Japanese style knives that are usually sharpened to 14° – 16° depending on the knife maker. Japanese style knives utilize a much harder steel, and are therefore more brittle than their