Caring for canvas: conserving stormy seas

Behind the glass of the North Gallery studio, a gale that has been yellowing since 1840 is slowly turning blue again. This is the diary of one painting's rescue — the kind of work visitors watch over our shoulders every weekday.

Week one: reading the wreck

Every rescue begins with looking. Under raking light we map every crack; under ultraviolet, old retouchings glow like bruises. This canvas had three generations of varnish, a relining from the 1920s, and a long-ago repair where someone — we salute their confidence — painted a wave with house paint.

Weeks two to six: lifting the years

Varnish comes off a square centimetre at a time, with cotton swabs and a solvent mixed weaker than you'd think. The moment the yellow lifts, the sea underneath is suddenly daylight again — visitors at the glass gasp at that moment at least once a day.

"Restoration is not making new. It is removing everything that isn't the painting."

The final coat

Losses are filled, colour is matched only where paint is genuinely missing, and a fresh, removable varnish goes on — our promise to the next century's restorers that they can undo everything we've done. The gale returns to the wall in spring, bluer than anyone living has seen it.