LONDON (AP) — How do you rebuild a Rothko? Slowly and with great care.

London's Tate Modern is putting Mark Rothko's mural "Black on Maroon" back on display Tuesday, more than a year and a half after it was defaced with black ink by a vandal trying to draw attention to an obscure artistic movement.

The gallery has spent 18 months working on the abstract painting, whose surface is made up of layers of oil, pigment, resin, egg and glue.

Tate experts said the ink soaked in as far as the back of the canvas, requiring delicate work to remove it and restore the painting's layers.

Wlodzimierz Umaniec received a two-year jail sentence for scrawling "a potential piece of yellowism" on the painting to draw attention to an artistic movement he co-founded.