Laura Cumming

Not the real room in the Prado around you, but the room in the painting as it mysteriously seems.

This is the first sensation that strikes when you see Las Meninas in the Prado.

A picture the size of life and fully as profound that you are walking into their world, becoming suddenly as present to these people as they are to you.

And in that moment, time stills in a flash of light in the darkness.

These brilliant little children, the princess and her attendants, twinkling out of a monumental volume of shadow that fills most of the high chamber in which they appear, away down at the bottom in this little pool of light, brief and bright as fireflies.

It's the most spectacular curtain-raiser in art, and it sets the whole tenor of the painting.

We are looking at the first of our paintings, and it is the Arnolfini Portrait, otherwise known as the Arnolfini Betrothal or the Arnolfini Marriage.

And in my lifetime, it's been called all three.

And that gives some idea of how often versions of the interpretation of this painting have changed.

It's a very small painting.

People think it's going to be enormous because it's so famous.

But in fact, it's not big.

About a foot and a half by two feet.

It hangs in the National Gallery in London, where people go in droves to look at it.

And I think it is, for the National Gallery in London, about as mysterious a painting as the Mona Lisa is in the Louvre.

Not yet nicked, we noticed.

And the reason the painting, I think, is so famous is...

is that it has a wild combination of amazing hyper-realism.

Jan van Eyck, the painter, is credited, possibly slight exaggeration here, but he's credited with inventing oil paint.

He uses it to describe the shining surfaces and the exact proportions of every object in the world so brilliantly.