Glowing UV diamond on the back of a hand

The night the stones came back from Antwerp I was the only one left on the third floor, and the building makes a particular noise after eleven, a tick in the pipes like something cooling. Mr Okonedo had gone home with his bad knee and left me the lamp. It is a long grey box with a violet tube that hums, and when you switch it on the whole room goes the colour of a bruise. Everything honest stays dark. Everything that has been lying lights up like a fairground.

Most of the parcel was rubbish: glass, cubic zirconia that would not take a hint, a paste ring somebody's grandmother had sworn was Victorian. Then came the last pouch, and a small stone the size of a lentil began to burn under the tube, a clean cold blue, the blue of the sea at Ardnamurchan on the one day I saw it. I held it under the glass for a long time. The facets threw thin fences of light across the bench, every edge drawn as fine as a pencil line.

I wrote the certificate at ten past three. Genuine, no treatment, faint blue fluorescence noted. Then I sat with the lamp humming and thought about how much of what we want is only a shape that shows when the right light falls on it. I thought about you, and the summer you told me I was too careful to be happy. I am still careful. But I am going to the seaside on Sunday, and I will bring the lamp for the pier, and you can tell me whether the gulls glow.

Love, Tessa