Sharpening knives and tools at home

Every knife loses its edge with use, and the one you use most goes blunt first. Garden tools go blunt too. Bringing an edge back at home takes a stone, a diamond steel or a pull-through sharpener, and a little practice.

How to tell a knife is blunt

Great British Chefs, the recipe publisher, suggests a tomato. A sharp edge grips the skin straight away and glides through the flesh without any pressure. A blunt one slips on the skin or dents the fruit.

The Royal Horticultural Society (RHS) uses a sheet of paper for garden knives and secateurs. Hold the paper up and rest the blade gently on its top edge. A sharp blade cuts through with very little effort, while a blunt pair of secateurs folds and crushes the paper.

What a honing steel does

A honing steel keeps a sharp edge in line between sharpenings. Once an edge has gone dull, Great British Chefs says it needs sharpening. It suggests honing once a week, and sharpening the blade on a diamond steel about once a month.

Its method goes like this.

  1. Lay a cloth on a chopping board and stand the tip of the steel on it, so the steel can't slip.
  2. Hold the heel of the blade against the steel at about 20 degrees.
  3. Draw the knife down in an arc, heel to tip, so the tip of the knife finishes at the tip of the steel.
  4. Do the same with the other side of the blade on the other side of the steel, and repeat a few times on alternate sides.

A training guide for school kitchens from the Institute of Child Nutrition, at the University of Mississippi, adds one step. Wash the knife after honing, to remove any bits of metal.

Sharpening on a whetstone

A whetstone is a block of fine grained stone. The RHS explains that "whet" is an old word for sharpen. Some stones are used with oil and others with water, and the RHS warns that the wrong one will spoil the stone. Many stones have a coarse side and a fine side.

The number on a stone is its grit. A lower number means a coarser stone, which takes metal off faster. Coarse stones are for very dull blades and for nicks. Fine stones, numbered in the thousands, smooth and polish the edge afterwards.

A water stone that needs soaking goes into water until the air bubbles stop rising. Which?, the consumer group, suggests about 10 minutes, or the time in the stone's instructions. A "splash and go" stone needs only a splash of water on top. Some fine stones can break if they are soaked, so check the instructions before you put one in water.

Which? suggests holding the knife at about 22 degrees to the stone, and gives a way to find it. Hold the blade upright on the stone, at 90 degrees. Tilt it halfway down, to 45 degrees. Then tilt it halfway again. Keep the same angle all the way along the blade.

Many Japanese knives are sharpened at a narrower angle, around 15 degrees, so check the knife maker's instructions for yours.

Which? then suggests about 10 strokes on the coarse side, at that angle and with moderate pressure, and about 10 on the fine side. As the blade is sharpened, a thin lip of metal called a burr forms along the edge. You then smooth the burr away on the fine side of the stone.

Pull-through sharpeners

A pull-through sharpener sets the angle for you. Great British Chefs says that makes it easy to use, and describes how.

  1. Hold the sharpener firmly with your free hand.
  2. Put the heel of the knife in the sharpening slot and draw the blade through, heel to tip. Use only the weight of your hand, and don't push down.
  3. Repeat a few times, then draw the blade through the finer honing slot several times.
  4. Wipe the blade with a cloth.

Which? points out that pull-through sharpeners are made for straight edges. The Institute of Child Nutrition's guide for school kitchens tells staff to avoid handheld sharpeners, which it calls dangerous to the user, and to use a whetstone, an electric sharpener or a sharpening service instead.

Keeping an edge for longer

Which? advises staying away from glass chopping boards, which blunt a knife quickly.

It also advises washing knives by hand in soapy water and drying them straight away. Its dishwasher advice says the heat makes a blade more likely to go dull.

The Health and Safety Executive (HSE) lists keeping knives sharp among the ways to reduce the risk of knife accidents in catering kitchens.

Garden tools and scissors

Spades and hoes pick up nicks from stones in the soil. The RHS suggests fixing the tool in a vice and working a metal file across the nicks, pushing it away and keeping to the same angle. It warns against making the blade too thin, because that weakens it. Most digging tools need this once or twice a year, depending on how often they're used.

Secateurs are sharpened on the angled side of the blade only. The RHS says to leave the flat side alone, because sharpening it spoils the way the blades bite. Afterwards, it suggests a few drops of oil on the pivot and spring. BBC Gardeners' World adds that blunt secateurs tear plant stems, which can let disease in.

For scissors, a professional sharpener interviewed by Family Handyman, the home improvement magazine, uses a whetstone and follows the angle already on each edge. He finds a bench stone works best when the scissors can be taken apart.

When to pay a professional sharpener

The RHS suggests a tool workshop when the damage is too severe to put right at home. It says the same of garden shears that are very blunt, or whose blades don't come apart. BBC Gardeners' World suggests having pruning saws sharpened professionally.

Carrying knives in public

GOV.UK sets out the law. It is illegal to carry most knives in public without a good reason, such as needing the knife for your work. A small folding pocketknife is the exception, if its cutting edge is 3 inches or shorter and it does not lock. A court decides whether a reason is good enough, and GOV.UK suggests asking your local police if you are unsure.

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