GIRL IN A GREEN GOWN by Carola HIcks (Chatto & Windus, £16.99)

One of the most famous pictures in the National Gallery — and one of the earliest secular paintings in Europe — shows a cold-eyed man and a woman with a swollen stomach and modestly downcast eyes, standing in front of a mirror, in their home. It was painted by Jan van Eyck, in the Netherlands, in 1434.

What it is about, and how did it end up in this country?

Carola Hicks was a distinguished art historian who sadly died last year before she could put the finishing touches to her book, which is subtitled The History and Mystery of the Arnolfini Portrait. It tells us almost everything about the portrait and its history.

She explains that the Arnolfinis — if that was their name — were rich merchants who had themselves painted with the idea of showing off their clothes and possessions, like a modern celebrity couple in Hello magazine.

The extraordinarily detailed background — the mirror, the chandelier, even the painter’s signature — is analysed in depth. There is much more than you see at first glance.

It is likely that the man and woman in the picture had no descendants and that the portrait was bought after their deaths by the Spanish royal family.

When Napoleon invaded Spain, his armies looted artworks on a massive scale and the portrait fell into the hands of an English officer, who sold it to the infant National Gallery, some 400 years after it was painted.

Carola did not live to answer her own question: why do we still like this picture today?

It had a huge influence on medieval Dutch painters, and then the Pre-Raphaelites, and it continues to inspire ‘cartoons, posters, T-shirts, fridge magnets, cufflinks shaped like the convex mirror, mugs’ and stamps.

Whether or not it really shows a wedding ceremony, it has become a symbol of marriage.

The book is fascinating. When you have read it, you may want to rush up to the National Gallery in London and take another long look at this enigmatic couple.