Grinding stones, for sharpening burins and other cutting tools

For smooth and precise cutting, it is essential that the tools are razor sharp. The tools can be sharpened with natural whetstones (Arkansas) or synthetic whetstones (India). Synthetic stones are composed of an abrasive and a binding agent. Always grind with a coolant, preferably oil.
Tools can also remain sharp for a long time by honing them (extremely fine grinding) on a piece of leather or hardwood.
With a lot of patience and practice, you will be able to keep your tools in excellent condition. Waterstones are often used for sharpening Japanese cutting tools. These stones are synthetic and usually soft, and can be used with water. The accompanying document provides a lot of information about these stones. It is also informative for sharpening in general. For detailed information (in English) about sharpening: 

grinding 

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Lyons, sharpening stones
Lyons, sharpening stones