How they make razor blades sharp

Every 24 hours, as many as 25,000 hairs grow up to half a millimetre on the face of the average adult male. The modern razor blade, honed to perfection, can cut its way through this stubble forest to give a close, smooth and safe shave.

Men began removing their fast-growing facial hair thousands of years ago, using slivers of flint and then bronze, and eventually iron blades. The world’s first steel-edged ‘cut-throat’ razors were introduced in Sheffield in 1680. But the modern type of disposable safety razor blade did not appear until 1901, when a Wisconsin travelling salesman, King Camp Gillette, and an engineer, William Nickerson, were granted a patent.

A razor blade starts its life as a continuous coil of rolled steel strip about four thousandths of an inch (0.1 mm) thick – about the same thickness as the hair it is designed to cut.

The steel is an alloy containing about 13 per cent chromium, which gives it increased hardness and resistance to corrosion. The hardness is increased further by heating the steel and then plunging it into cool fluid.

The shaving edge is produced by grinding. The strip passes through three sets of grinding wheels, each grinding finer than the one before. The wheels are set at different angles to give what is called a gothic-arch (curved) cross-section. The shape is stronger than a straight-sided wedge. The sharpness of the blade is expressed as the radius of the curve forming the extreme tip of the cutting edge: about five-hundred thousandths of a millimetre.

After grinding, the cutting edge is polished by rotating leather wheels. On a microscopic scale, however, the edge is still rough and because of friction, liable to snag the hairs and cause discomfort. To protect the cutting tip and reduce friction, the blade is given three successive coatings: chromium, ceramic and the plastic PIPE, more familiar as the slippery non-stick coating on pans. The chromium resists corrosion, the ceramic reduces wear and the PTFE produces lubrication.

The coatings are each less than one-hundred thousandths of a millimetre thick.

The razor blade fits into a holder with a handle which is comfortable to hold and has a head which may be adjustable and may screw open to take the blade.

Wet and dry cut A wet beard hair cut by a razor bladeĀ  shows a much cleaner cut than one done by an electric razor. Wetting the beard, necessary for shaving with a safety razor, makes it easier to cut. A dry whisker is as hard to cut as a copper wire of the same thickness.