by Alison Oldham Mummy was a brownish paint valued for its translucent qualities and used for spooky shadows until early in the 19th century. Then one of its components became problematic – mummified corpses – and it went out of circulation. The modern connotations of M

Mummy was a brownish paint valued for its translucent qualities and used for spooky shadows until early in the 19th century.

Then one of its components became problematic - mummified corpses - and it went out of circulation.

The modern connotations of Mummy make it a homely name for a ghoulish substance. Caput Mortuum, Latin for death's head, is the opposite - a creepy name for a deep red-brown paint made from innocuous red iron oxide.

During a personal preview of paintings for his exhibition Rocks and Peat, currently at the Highgate Gallery, Brian Knox drew my attention to the part Caput Mortuum plays in a dramatically angular portrait of his wife Lesley.

The couple met as collectors of contemporary art competing for an Amanda Faulkner painting at the gallery founded by a neighbour in Highgate, Angela Flowers. Lesley paid and they share the painting.

The title of Knox's show comes from his main subjects - contorted rock formations near Europie in the Outer Hebrides and the islands' peat hags (dialect for firm spots in bogs). Swirling patterns of rock strata in cliffs and rectangular patterns left by a peat-cutting spade have been starting points for Knox's ever less representational compositions.

Into these he introduces geometrical forms which reflect the intense blues and greens of the Hebridean sea and sky, as in the Rocks painting pictured.

Recently he has developed a series of Sound paintings with linear forms based on the sky, sea and shore of the Sound of Harris.

Knox feels a bond with the Hebridean landscape for its similarities to the north of Ireland, which he came to know on childhood visits to his father's family living there. But he finds it "vital to evade the seductions of the glitter on the sea and the splashes of light on white houses which have ruined many Irish painters."

Four years ago, the cut walls of peat became for him a refuge from the picturesque. He moved on to the rock formations for inspiration but now turns seawards, to make "rough notes to be deliberately misinterpreted in the studio, with colour schemes kicked off an expensive Dutch tube of turquoise". After working for nearly 40 years on the Stock Exchange, he can afford costly paint.

As a schoolboy at Winchester, Brian Knox felt deprived of a real chance to make art and suppressed aspirations to be an architect when a student at Oxford in favour of a City career with more immediate financial reward.

He hoped to employ architects on his future homes and now he and his wife have three houses, all adventurously designed. Knox is an authority on Czech and Polish architecture. He has written two books on these subjects and contributed to the forthcoming Oxford Companion to Architecture.

Through collecting the work of Euan Uglow and other painters connected with the Slade, he was inspired to try his own hand and then had the privilege of attending classes at the school for a year. Sadly, it coincided with the onset of cancer - now treated - but it made, he said, "a grim year chasing down dead ends".

Out of his experimentation there emerged a fascination with patterns initially as background to still lifes. "It started with a brick wall," he says. "It was not any brick wall but one of grey-violet-yellow bricks from a now closed works in Leicestershire."

He moved on to an interest in textiles and carpets, especially Berber rugs where dark browns were strongest. First the rugs appeared behind life models, then covered the lower three quarters of the canvas, topped by artefacts like a skull or glass dish.

Finally and exultantly, pattern took over the whole space. Rocks and Peat reveals where this led him. It's the first London exhibition outside his Shoreditch studio for collector-turned-painter Knox, who is 75 in February.

At the Highgate Literary and Scientific Institution, 11 South Grove, Highgate, until next Thursday, January 25. Open Wednesday-Friday 1pm-5pm, Saturday 11am-4pm, Sunday 11am-5pm.