An enamel kettle is a small piece of kitchen history: a rose transfer, a speckled granite finish, a thin gold line at the rim, a whistle you can still hear from the next room. Age brings two things with it — chalky limescale inside and a dull, slightly tacky film outside. The instinct is to reach for the strongest cleaner in the cupboard and scrub until something happens. That is precisely how decorated enamel loses its shine, its gold band and half its pattern. What follows is the slow version: soft tools, mild acid on the inside, and almost nothing abrasive anywhere.

Why enamel punishes the usual cleaning advice

Vitreous enamel is powdered glass fused onto steel in a kiln. The result is hard, glossy and chemically fairly tough, but it is still glass. It chips when knocked, crazes into a fine web of cracks when hit by sudden temperature change, and dulls wherever something abrasive touches it.

Decoration matters too. Some patterns are printed and then sealed under the final glaze layer, which makes them surprisingly durable. Gold rims, lustre bands, hand-painted details and many older transfers sit on top of the glaze, where a fingernail — or a nylon scrubber — can lift them. Acid lifts scale but also eats into gold. Abrasive powder lifts stains and takes the pattern with them. Once you know which surface you are dealing with, the whole routine becomes obvious.

Two minutes of looking before you touch water

Set the kettle on a towel in good light and examine it dry. Water is the enemy of rust, so find rust first.

• Rim and spout: run a fingertip around both. Chips here are common and usually mean bare steel underneath.
• Body: look for crazing — hairline cracks that look like a shattered windscreen, but lie flat.
• Rust: orange freckles at the base seam, around rivets, under handle brackets, inside the spout.
• Interior: white chalky scale, a brown tannin tide line, or grey metal where enamel has worn away.
• Fittings: wooden or Bakelite handles, brass rivets, a whistle cap with a rubber gasket that may be perished.

If you find active rust or a chip that is lifting, clean only lightly with a barely damp cloth and treat the kettle as a display piece. If the inside is sound, you can clean it properly. And if you plan to boil drinking water in it, the interior needs to be intact enamel rather than exposed steel.

Descaling the inside, and only the inside

Limescale is calcium carbonate, and mild acid dissolves it. Citric acid is cheap, odourless and easier on decoration than vinegar, which is why it is the better first choice.

1. Fill the kettle with fresh water and add one to two tablespoons of citric acid per litre. If you prefer white vinegar, mix it half and half with water.
2. Bring it to a boil, then switch off. Do not keep it rolling; the reaction is finished, and vinegar fumes are unpleasant. Open a window if you use vinegar.
3. Cover and leave it. Thirty minutes for a light haze, several hours or overnight for a thick crust.
4. Pour it out and inspect. If chalky patches remain, repeat with a fresh batch. Never chip at scale with a knife, a screwdriver or a metal spoon.
5. Rinse three times with warm water, then boil a full kettle of fresh water and discard it. Do that twice. Acid left behind will taste of itself.

The real risk is the exterior. Splashes etch glaze and are especially unkind to gold. Work over a sink with the kettle steady, wipe any drip off the outside immediately with a damp cloth, and rinse the whole outside when you have finished.

Tannin stains and the brown tide line

Kettles used for tea, or simply kept near a stove, collect a brown film inside: tannin plus cooking grease. Tannin responds to oxygen rather than acid.

• Oxygen-based cleaner (sodium percarbonate, sold as oxygen bleach or laundry stain remover) does the work. Dissolve it in warm — not boiling — water at the ratio on the package, fill the kettle, soak for one to four hours, then rinse thoroughly.
• Light film: a paste of baking soda and a little water, applied with your fingertips, left for ten minutes, then rinsed. No scrubbing.
• Skip chlorine bleach. It can dull glaze, attack decoration and corrode fittings, and it is miserable to rinse out of a vessel you may later boil water in.
• Staining inside crazing lines will not lift. It has become part of the surface. Leave it; it reads as age, not dirt.

Everything that works fast on enamel works by taking off a layer of something. Sometimes that layer is the decoration.

The outside: soap, warm water and a very light hand

Most exterior dullness is simply film — kitchen grease, dust, old polish. Clean it in stages, and stop as soon as the surface looks better.

1. Warm water with one drop of mild dish soap, applied with a soft microfiber cloth. Wipe, do not scrub.
2. Repeat with fresh soapy water if the cloth keeps coming away grey.
3. For scuffs and dried-on spots, make a thin paste of baking soda and water. Work it with a fingertip in small circles for about thirty seconds, only on the spot that needs it, then rinse.
4. On plain white enamel with no gold or printed decoration, a dab of ordinary white toothpaste on a cloth can shift a stubborn mark. Test it on the underside first.
5. Rinse with clean warm water, then dry immediately with a soft cloth so you do not leave water spots behind.
6. Dry the seams properly: around rivets, the base seam, the spout join and under the handle brackets.

Never use these on decorated enamel

• Steel wool, scouring pads, wire brushes or sandpaper.
• Abrasive cream cleansers and powdered cleansers.
• Chlorine bleach or oven cleaner.
• A dishwasher. The detergent is aggressive and the drying cycle is hot.
• Metal polish on gold or lustre bands — it removes them rather than brightening them.Photo: Melike B / Pexels