Turn the painting over

Most people hang a painting and never see it again from behind. That is a pity, because the back is where a painting keeps its paperwork. Nobody designs the back of a canvas. Things just collect there: the supplier’s stamp, a framer’s sticker, a dealer’s number in chalk, a note from someone who owned it fifty years ago. Each was put there for a practical reason, and together they read like a passport.

The artist’s own marks

Some painters signed the front and wrote everything else on the back: the title, the date, the place. Some left marks that are harder to fake than a signature. Waddington’s, the Toronto auction house, lists a few. The French painter Édouard Cortès pricked his canvases with a pin. The Canadian painter Clarence Gagnon sometimes pressed his thumbprint into the back. On one work by the English animal painter Thomas Sidney Cooper, they found his seal in red wax and his initials pressed into the wood.

Not every note on the back is about the painting. The Canadian painter John Little once wrote out the full 1935 roster of the Montreal Royals baseball team on a stretcher bar. It tells you nothing about the picture and a great deal about the man.

The canvas has a maker too

Artists bought ready-primed canvas from suppliers, the old “colourmen”, and many suppliers stamped their name on the back. Museums use these stamps and labels to date paintings, because suppliers changed their stamp designs over the years. An Art UK discussion, drawing on the National Portrait Gallery’s research, notes that one Winsor & Newton stamp design was common from about 1888 to 1905. A painting cannot be older than its canvas.

The reverse does not hold the other way. A London stamp proves the canvas came from London, not the painter. Painters everywhere bought English and French canvas.

The wooden frame behind the canvas

The stretcher, the wooden frame the canvas is pulled over, carries its own evidence. Roseberys, the London auctioneers, point out that the nails used to join the stretcher and the tacks that hold the canvas can help date a painting. Waddington’s adds that American stretcher makers changed their methods roughly every decade from 1840 to 1900, and that staples began to replace nails in the 1940s. A painting said to be from 1920 that is stapled to its stretcher has either been restretched or is not from 1920. Either way, you want to know.

Stretchers also break. Damp, heat and rough handling all take their toll, and replacements are common. A new stretcher is not a bad sign. It is just a gap in the story.

Labels, stencils and chalk

Galleries, dealers and auction houses have long marked the works that pass through their hands: stock numbers in ink, chalk or grease pencil, printed labels, stencils on the stretcher. Roseberys notes that old stencil marks and chalk letters can reveal a painting’s sale history. Exhibition labels do the same for its public life: where it hung, and when.

Labels can also be faked or moved from one painting to another. A label is a lead to follow, not a fact on its own.

Repairs show from behind

Lining, gluing a new canvas behind an old one to strengthen it, is easier to see from the back than the front. Waddington’s mentions traces of glue at the edges of the canvas. Patches show even more plainly. Neither is a scandal; old paintings get repaired. But a seller who says “untouched” should be able to show you an untouched back.

Sometimes the back holds something else entirely. Waddington’s records a painting whose title on the reverse did not match the picture on the front. Behind it, in the same frame, was a second painting.

What to do with your own

Photograph the back before anyone reframes, relines or cleans the work. Do not peel off labels, however tatty, and do not let a framer throw away an old backing board without showing it to you first. If you copy down what you find, copy it exactly, spelling mistakes and all.

The back of a painting is rarely beautiful. It is usually honest. Paint can be retouched to look like anything. Chalk on old wood is harder to arrange.