Sharpening a graver or burin requires either a sharpening stone or wheel. Whetstones were traded and used for sharpening weapons, tools and knives. The cloth is used for blade alignment and sharpening. The scabbard also has a sharpening stone and folding saw blade. A grindstone is a round sharpening stone used for grinding or sharpening ferrous tools. Edged tools were kept sharp with sharpening stones from Norway. Craftsmen in Tanegashima have kept alive traditional techniques for forging and sharpening iron tools. The opening sound is a recording of the songwriters' father sharpening knives. Grinding is generally done with some type of sharpening stone. Men shaved with straight razors that needed sharpening every day using a leather strop. Silicon carbide is the same material used in many sharpening stones or discs. There are many ways of sharpening tools. People sang chants as they worked at grinding corn or sharpening tools. Hard-tempered edges last longer but sharpening them is difficult. Some shapes are designed for specific purposes such as sharpening scythes, drills or serrations.