Looking after the knife you made

A knife you made yourself is far more likely to be carbon steel than anything you would buy, because carbon steel is easier to heat-treat at home and takes a better edge for the effort. It is also the steel that rusts if you look at it wrongly, and that is the first enemy.

The second is the edge, and it is misunderstood almost universally. A knife that feels blunt has usually not lost any steel at all — the very fine edge has rolled over to one side, and it can be pushed back in about fifteen seconds without removing anything. Confusing that with sharpening is why a lot of knives get ground away far faster than they need to be.

What rusts a knife

Being put away damp, once

What "gone blunt" usually means

A rolled edge, not a worn one

The habit that solves most of it

Wipe, dry, put away

What ends a handle

A dishwasher, in one cycle

Carbon steel oxidises. That is not a defect to be fought so much as a process to be directed, because there are two kinds of oxidation and they are not the same thing.

Patina is the stable grey-blue-brown film that forms on a used carbon blade, and it is protective: it occupies the surface so that red rust has nowhere to start. It arrives on its own within a few weeks of ordinary use, particularly if the knife cuts anything acidic, and a great many makers let it happen rather than polishing it off.

Red rust is the powdery orange kind, it is not protective, and it pits the steel underneath. Once it has pitted, the pit is permanent — you can remove the rust and the small crater stays.

What actually prevents it:

• Dry it immediately, every time — This is ninety per cent of the whole subject. A carbon blade left wet on a draining board for an afternoon will have started rusting by evening. Wipe it before you put it down, not after you have finished cooking.
• Never leave it in the sink — The single commonest way a good knife is ruined, and it also puts an edge against crockery, which is the other half of the damage.
• A very light oil for storage — A wipe of food-safe mineral oil — sold as butcher block or maintenance oil — before putting a knife away for weeks. Not olive or vegetable oil, which go rancid and sticky.
• Store it dry and with air round it — A magnetic strip, a block, or a sheath that is not leather. Leather holds moisture against steel and is a classic way to rust a blade you carefully looked after.
• If red rust appears — Deal with it early. A light film comes off with a cork or a wine cork and a little oil, or with the finest abrasive you are willing to use. Leaving it is what turns a mark into a pit.

A sharp edge is a very thin piece of steel, and thin steel bends. In use it rolls fractionally over to one side, and a rolled edge presents a curve rather than an apex to whatever you are cutting — which feels exactly like bluntness and is not.

Honing pushes that roll back straight. It removes essentially no metal, takes a few seconds, and restores most of the performance. A smooth steel or a ceramic rod does it; the ridged steel that came with a knife block is a mild abrasive rather than a true hone and is less gentle than it looks.

Sharpening removes metal to form a new apex, because the old one has actually worn away or been damaged. It is done on stones, it takes real skill, and every time you do it the knife gets very slightly smaller.

The practical consequence: hone often and sharpen rarely. A kitchen knife in regular use might want honing every week or two and sharpening once or twice a year. Somebody who sharpens whenever the knife feels dull is grinding away a blade that mostly needed straightening.

• Never the dishwasher — Not as a rule of thumb — as an absolute. The combination of prolonged heat, moisture and detergent will swell and crack a natural handle, degrade most adhesives, and rust a carbon blade, all in one cycle. This is the single fastest way to destroy a knife somebody made.
• Natural wood wants oil occasionally — A wipe of the same food-safe mineral oil every few months keeps it from drying and shrinking away from the tang. Takes a minute.
• Stabilised wood and synthetics need nothing — If the handle was stabilised or is a composite, it is already sealed. Oiling does no harm and no good.
• Watch the joint, not the wood — The first sign of trouble is a hairline gap where the handle meets the bolster or the tang. That is moisture getting in, and it is much easier to address before it becomes movement.

1. 1

   Step 1: After every use: wipe, dry, put away

   Warm water, a cloth, dry immediately, back on the magnetic strip. Never into the sink, never onto the draining board, never into a drawer loose against other steel.

   You will know it worked when: Rust prevented, edge protected.

2. 2

   Step 2: Every week or two: a few passes on a hone

   Or whenever it starts feeling less keen. Seconds, and it removes almost nothing.

   You will know it worked when: Most of the sharpness back, for free.

3. 3

   Step 3: Every few months: a wipe of oil on blade and handle

   Food-safe mineral oil. Especially before a knife goes away for a while.

   You will know it worked when: A blade that will not surprise you when you next open the drawer.

4. 4

   Step 4: Once or twice a year: actual sharpening

   On stones, on a guided system, or by somebody who does it properly. Rarely, and deliberately.

   You will know it worked when: A knife that lasts decades rather than years.

• My carbon blade has gone grey and blotchy. Have I ruined it? — Almost certainly the opposite — that is patina, and it is protective. The stable grey-blue-brown film that forms on a used carbon blade occupies the surface so red rust has nowhere to start. Powdery orange rust is the one to act on, because it pits the steel and the pit stays after the rust is gone.
• How often should I sharpen it? — Far less often than most people do. A knife that feels dull has usually rolled its edge rather than worn it, and a few seconds on a hone straightens that without removing metal. Honing every week or two and sharpening once or twice a year is a normal cycle for a kitchen knife in regular use.
• Is a honing steel the same as a sharpening steel? — Not quite, and the names are used interchangeably in shops. A smooth steel or ceramic rod hones — it straightens a rolled edge and removes almost nothing. The ridged steel that comes with a knife block is a mild abrasive and does remove metal, so it is gentler than a stone and less gentle than it appears.