Blue

Vita Sackville-West planted Sissinghurst as a series of rooms, each held to one range of colour — the White Garden in white, green, grey and silver; the Purple Border; the Cottage Garden in nothing but hot ones. She called it amusing to make one-colour gardens. It is a good way to hang a wall too, and it is how most people actually choose a print: not by century or by technique, but by whether it will live with the room.

This is the blue room. Every sheet in it was measured rather than eyed: blue accounts for at least three fifths of the printed colour, and colour covers at least a third of the sheet. Nothing is here because it has a blue sky in the corner.

One pigment runs through most of it. Anna Atkins's algae are not printed at all — they are cyanotypes, iron salts turned Prussian blue by sunlight, the same compound a chemist first made by accident in Berlin around 1706. Eighty years after that accident the pigment reached Japan through Nagasaki as bero-ai, and by the 1830s it was cheap enough for a printer to lay across a whole sheet: that is the ground of Hokusai's bullfinch. Munch and Monet reached for the industrial descendants of the same chemistry.

So the room holds together for a reason that is not decorative. It is one colour, arrived at four different ways, over a hundred and thirty years.