"He looked like an English farmer, with his rough black coat and heavy boots, and his cold, hard expression." This was the French painter Eugene Delacroix's unimpressed verdict on Joseph Mallord William Turner, the maker of the apocalyptic, spray-glazed seascapes and light-veiled landscapes that have become icons for today's gallery-going middle classes. Universal reverence is new: Mark Twain described Turner's passionate painting of dying slaves on a ship being thrown overboard at sunset as "Cat having a fit in a platter of tomatoes".
In life, Turner was a rough diamond. His father was a Soho barber with a West Country twang that may have mixed with Turner's boyhood cockney (lesser men mocked his vowels when he lectured on perspective at the Royal Academy). With his short, stocky body, bandy legs, high colour and "penetrating gaze", Turner was often taken for a sailor. In his last years, living secretively by the Thames with his mistress, Mrs Booth, he passed as "Admiral Booth", getting up early to sit on the terrace he had built to watch the sun rise over the river. The way he stared straight at the sun frightened those who saw him - wouldn't it damage his eyesight? "No more than it would hurt yours to look at a candle," said Turner.
Turner was a practical man. His technical skill raised the status of watercolour and brought it closer to oil. The challenge was to paint light: he used "stopping out" varnish to leave areas of white paper shining out, scratched highlights with one "eagle-claw of a thumbnail", and swept off pigment with a sponge or breadcrumbs. He was practical about money, too. Sir Walter Scott remarked: "Turner's palm is as itchy as his fingers are ingenious and he will, take my word for it, do nothing without cash, and everything for it." He left an estate of around £4m in today's money, partly through establishing his own commercial gallery off Harley Street, where admirers such as John Ruskin were welcome. Late in life, Turner was able to turn down an offer of £100,000 (around £2.5m today) for the contents of his gallery, so that, on his death, he left a large body of work to the nation.
The new Oxford Companion contains 32 colour plates, a 13-page chronology and a thematic contents list that helps the reader navigate the alphabetical entries. It is particularly good on concrete matters such as Turner's will (a knotty topic, given that his central aim of setting up a fund for destitute artists was never achieved) and the changing market in Turner's work. The chief editor is Evelyn Joll, the chairman of Agnew's, which has been Turner's principal dealer for the past hundred years. Other contributors include authoritative Turner scholars such as Andrew Wilton, Ian Warrell and Eric Shanes, who wrote the essays for the catalogue to the Royal Academy's current exhibition "Turner: the great watercolours", which is not to be missed.
Turner left £20,000 to the Royal Academy, partly for the biennial award of a gold "Turner Medal" for landscape painting, which was to be worth "about £20" (then the equivalent of an annual income). Today, the RA stumps up for a bronze Turner medal, plus the niggardly sum of £50. Meanwhile, the Tate Gallery, in a white blaze of media attention, shortlists narcissistic non-painters such as Tracey Emin for what is cheekily called the Turner Prize. Unlike Emin and Sarah Lucas, whose joint artistic offering at Tate Modern is a larger-than-life video of themselves puffing away and glugging down the vino at ten in the morning, Turner's art was genuinely public - about nature, war, history, social unrest, while he kept secret his private life and generous intake of "brown sherry". He had two daughters with Sarah Danby, the mistress he never publicly acknowledged, then lived out his declining years anonymously with his former Margate landlady. The "dark, kindly mannered" Mrs Booth seems to have soothed his despairing moods with domestic happiness - they called each other "old 'un" and "dear" - though she apparently paid all their household expenses.
One occasional drawback to the generally excellent Companion is a lack of dovetailing between the entries. I had to read Hannah and Sarah Danby's entries several times before I was sure that Sarah was the aunt of Hannah, the sad figure, dressed in dingy white flannel and with her eczematous face covered, who looked after Turner's gallery so poorly. The rain came in through the skylights, her seven Manx cats walked with wet feet over unhung watercolours, and one of the paintings served as a cat flap.
At ten in the morning, just before Turner died, the sun poured into his bedroom overlooking the river. Ruskin, who had a better way with words than Turner, records him saying in his last weeks: "The Sun is God." Even if that was Ruskin's invention, Turner's paintings, shining out from the dark red walls in the dust and decay of his gallery, silently asserted the same terrifying hope.