An earlier questioner asked how metal blades in wet shavers lost their sharpness so easily on human hair. One answer said that alternating blades in a razor made each one last longer than if left in place until they became blunt. So subsequently the Last Word posed a second question. Does any reader know why alternating blades makes each one last longer?
鈥� Keeping razors away from water will stop the cutting edge corroding, so this might explain why alternating blades extends each one鈥檚 life.
Rust consists of hydrated ferric oxides with varying quantities of water, meaning rust is a poorly defined chemical. Rust will form on a wet blade edge and the water content in the rust will increase the longer the edge stays wet, so the rust will become bulkier and the blade blunter.
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If the blade is placed in a dry environment, for example, under a so-called 鈥渕agic pyramid鈥� or perhaps more usefully in a cupboard drawer, then the amount of water could decrease, the rust will subsequently become less bulky and so the blade will feel sharper.
鈥淜eeping razors away from water stops corrosion, explaining why alternating blades extends their life鈥�
David Muir, Edinburgh, UK
鈥� It is sound economics to go on using deteriorating equipment until the cost of continued usage equals or exceeds (just) the cost of replacement. When you use two razors in turn, the cost of a 鈥渞eplacement decision鈥� doubles, so will be delayed until both have got worse. This also helps us understand how a set of seven expensive cutthroat razors might easily last a lifetime, by achieving an equilibrium where the owner can neither bear to use any of them nor afford seven new ones.
John McCrea, Banstead, Surrey, UK
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