Enamel mugs are bought from a photograph and judged after two hundred dishwasher cycles. These four questions decide the second part.

First, is it actually enamel?

Vitreous enamel is powdered glass fused to steel in a kiln. Powder-coated steel is paint baked at a much lower temperature. Both get called enamel and they look the same new.

Real enamel is oven safe and glassy to the touch, and a spoon will not scratch it. Painted steel scratches, is not oven safe and will not survive a commercial dishwasher. If a supplier will not say which one they are quoting, that is your answer.

Ask what happens at the rim

Almost every chip starts at the lip, because that is what gets hit. A rolled rim folds the steel over on itself and leaves bare stainless at that point, so there is no glass there to chip.

A coloured rim is enamel taken over the lip. It is the better-looking finish and the more fragile one. Both are legitimate; only one of them is usually explained.

Ask how many coats

A proper build is a ground coat that bonds to the steel plus one or more cover coats. A single direct-on coat is thinner, cheaper and chips sooner.

Nobody volunteers this number. Ask for it and put it on the purchase order, and you have made the single most useful comparison between two quotes that otherwise look identical.

Match the gauge to the room

Enamel usually fails because the steel underneath moved. A thin mug dents when it is dropped into a bus tub and the glaze over the dent crazes and lifts.

For commercial service, buy heavier gauge. For a shelf, a gift box or a homeware line, do not — the extra weight costs money in freight and nobody will ever notice the benefit.

And check the logo was fired

Run a fingernail over the edge of the print. A fired mark is flush, because it has vitrified into the surface. An applied print has an edge you can feel.

This is the difference between branding that outlasts the mug and branding that is patchy by the second winter.