Abrasion and scratching

Where the obvious answer is wrong

Cases where the treatment that removes the problem is the treatment that ruins the surface it is on.

• Can I use a limescale remover on my bathroom taps?

  The visible part of a modern tap is a plated, physical-vapour-deposited or powder-coated finish a few microns thick, not solid metal. The manufacturer's care sheet states that PVD finishes must not meet cleaners containing ammonia, bleach or acid, which excludes most limescale removers and a good share of bathroom sprays. Because the finish is microns thick there is no margin: material lost is coating lost, the dulling is progressive, and it cannot be polished back because there is nothing underneath to polish.

Assessed and found wanting

Widely repeated techniques in this area that the evidence does not support, or supports only in part.

• Never use an abrasive in the bathroom

  Disputed

  Right about the bath, the taps and the mirror. Wrong about the toilet and basin, where the manufacturer permits a soft abrasive outright.

• Toothpaste as a metal polish

  Does not work

  A mild abrasive in a tube, and the tap manufacturer names it specifically among the things that must not be left on the finish.

The records

• Relative hardness

  Science

  Whether an abrasive scratches a surface depends on which is harder. That is the entire question, and it is knowable in advance.

• Mechanical action and abrasion

  Science

  Physical force does a large share of all cleaning, and abrasive hardness relative to the surface decides whether it cleans or destroys.

• Gloss and light scattering

  Science

  Gloss is smoothness at a scale too small to see. Polish a patch of a matt wall and it reflects differently — the dirt is gone and the mark remains.

• Polishing removes metal

  Science

  Every polish takes a little of the object away. On solid metal that is a slow cost; on a plated one it is a countdown, and the end of it looks like more tarnish.

• Steel wool

  Equipment

  A metal abrasive that scratches most household surfaces and leaves iron particles behind on the rest — which then rust and look like a stain the surface has produced.

• Non-scratch pad

  Equipment

  The middle setting between a cloth and a scourer. It is still an abrasive — 'non-scratch' is a claim about a class of surface, not about all of them.

• Melamine foam

  Equipment

  Not a sponge and not a cleaner: an extremely fine open abrasive. It removes marks by sanding them, which is why it dulls anything with a finish on it.

• Scouring powder

  Cleaning agent

  An abrasive suspended in a carrier, sometimes with bleach added. What decides whether it is safe is the hardness of the mineral against the hardness of the surface.

• Mild cream cleanser

  Cleaning agent

  A liquid carrying a fine soft abrasive. The trade answer for water marks and light staining on stainless steel — and not the same thing as scouring powder.

• Metal polish

  Cleaning agent

  A very fine abrasive with a mild chemical assist. Every use removes metal, which is why polishing a plated or antique item is a one-way decision.

• The melamine sponge cleans anything

  Claim or technique

  It removes marks nothing else does, and the reason is that it is sanding them off — which is a fact about every surface it is used on.

• Plated and coated tap finishes

  Material or surface

  Modern taps are a coating on a metal, microns thick. The finish decides the rules, and the rules genuinely differ between finishes on the same basin.

• Vehicle clear coat

  Material or surface

  A transparent film a fraction of a millimetre thick doing all the work. Everything that looks like a stain on car paint is usually an etch in this layer.