For the longest time pictures were brick-shaped. Photographs in an album and portraits on the wall were often pre-figured to the Golden Ratio, that pleasing aspect that had mathematical as well as aesthetic qualities.

When Instagram came along it was decided by the cognoscenti that the “square was the new rectangle”.

But Instagram itself was calling on the retro feel of the 1960s Kodak Instamatics. As always what was new, was old, refashioned.

JMW Turner (1775-1851) got their first. Or at least got there earlier.

The perennial innovator produced a series of square canvases later in his life and the very squareness of the squares had the Squares reaching for their smelling salts.

He came under fire in the press, his audiences were shocked and mystified and even friend and critic John Ruskin said the old man’s work was “indicative of mental illness”.

For the first time ever Turner’s square oil paintings are shown together in Late Turner: Painting Set Free, the blockbuster exhibition at Tate Britain.

Co-curator David Blayney Brown said: “All of these paintings are of extraordinarily imaginative subjects and they take us deep into Turner’s psyche.”

The exhibition sets out to show that Turner’s last 16 years (1835-50) were a golden age where the driven painter was able to call on a lifetime’s worth of skill and memory to liberate his craft and push it into untried areas.

Co-curator David Blayney Brown said: “In his later years Turner was as inventive in his approach to media, materials and ways of working as he was in his subject matter.”

Late Turner: Painting Set Free

Tate Britain

Until Jan 25, Tate Britain, £15, tate.org.uk