Gainsborough painted the most refined and delicate portraits of any British artist and the most romantic landscapes before Turner. In his mature paintings he was a master of evocative brushwork, deployed with uncanny precision. Yet in person he was wild, impetuous, generous to a fault and obsessed with women. Despite earning huge sums he was always short of money. He was often the worse for drink, but even when perfectly sober he seldom appeared entirely sane, flinging his arms wildly around as his talk fizzed and bubbled. His friend David Garrick recognised his extraordinary gifts: ‘His cranium was so crammed with genius of every kind that it is in danger of bursting upon you, like a steam-engine overcharged, which, were it duly regulated, its powers would be as great.’

When it came to making pictures, Gainsborough managed consistently to harness his extraordinary energy. He brought to all his paintings, drawings and printmaking the most painstaking care and technical expertise. But, as Garrick suggested, there was more to him than that, including a passion for making music and a remarkable feel for language, which comes jumping off the page in his brilliant correspondence. Gainsborough’s letters could be downright filthy and early 19th-century prudes, alas, destroyed a large number of them. Nonetheless, enough survive, all published in 2001 in a collection edited by John Hayes. Here, Gainsborough comes alive in wonderful turns of phrase: ‘When the streets are paved with Brilliants and the Skies made of Rainbows’; ‘When he drops you’ll have nothing but poor old nature’s book to look in. You’ll be left to grope it out alone, scratching your pate in the dark, or by a farthing candle.’

Some of Gainsborough’s compulsive double entendres turn upon slang and were missed by Hayes. For example, he thought that Gainsborough was worried about standing at his easel when he wrote, ‘I shall come this Autumn to Exmouth to bathe in order to stand next Winter.’ In fact he was worried about whether he could get it up: ‘to stand’ meant to have an erection. The reason that Gainsborough was concerned about his sexual health is that he had suffered several times from venereal disease, the worst episode of which lasted through 1763 and beyond, when he was so ill that his death was mistakenly announced in the Bath Journal.

At the time, Gainsborough was self-pitying: ‘Nobody can think what I have suffered for a moment’s gratification.’ The experience did not, though, remotely cure him of his fascination with women. He could still find himself diverted on the way to meet a friend by the need for a quick one with ‘a little Venus rising from the Sea in my way to my Lodgings … her hair was damned red’. Signing off a letter, his thoughts would turn in the same direction: ‘If you was a Lady I would say what I have often said up in a corner by way of making the most of the last Inch. Yours up to the hilt. TG’.

In his shrewd and entertaining biography, James Hamilton misses none of the naughty bits and even finds unsuspected double entendres in the pictures, not least in Gainsborough’s most familiar and well-loved composition, Mr and Mrs Andrews. The bag for Robert Andrews’s shot and powder hangs next to his gun and, Hamilton says, suggests male genitalia. He is right. Gainsborough had been at school with Andrews and clearly thought that a little schoolboy humour would not go amiss. Having set up the joke with the suggestive bag, Gainsborough deliberately left the final detail until last, which was to be a clinching visual pun in a space on Mrs Andrews’s lap he had left blank. We can see what was intended: a pheasant, or, to be precise, a cock. At that point, Mrs Andrews must have called a halt. The couple took the picture, unfinished as it was. It was not seen in public until 1927.

Hamilton’s approach is influenced by his perception that Gainsborough owed much to Hogarth, a point that has been missed or underplayed elsewhere. As Hamilton shows, the evidence has always been in plain sight, beginning with Gainsborough’s early training in and around Hogarth’s own academy. Then there was Hogarth’s patronage of Gainsborough as a very young man, when he asked him to contribute a view of the Charterhouse to the Court Room of the Foundling Hospital. There are echoes of Hogarth’s work in a number of Gainsborough’s compositions and they had close mutual friends, including Garrick and the landowner Robert Price of Foxley.                      

This valuable insight informs both Hamilton’s exploration of Gainsborough’s art and his thorough and imaginative interpretation of the life, which has been achieved through a fresh study of the paintings, an examination of the documents and a shrewd reading of sources. Hamilton also appears to have visited any part of the countryside that Gainsborough knew and to have sought out every surviving building that he either occupied or visited. He tells us, after roaming about the Auberies, the Andrews estate in Suffolk, that the oak tree in Gainsborough’s painting is still there. We also learn that Gainsborough’s grand house at 17 King’s Circus in Bath has its mews building intact, just as it was in Gainsborough’s time (‘a miraculous survival’), and that his front-door lamp is still in place and in working order.

He describes, too, how a stay at Wilton House in 1764 with the tenth Earl of Pembroke – whose eccentric behaviour puts Gainsborough’s impetuosity in the shade – proved a turning point by giving him a profound new understanding of van Dyck. Gainsborough copied van Dyck’s vast group portrait of the fourth Earl of Pembroke’s family; one week of living with the van Dycks at Wilton House informed every picture that Gainsborough painted thereafter. The famous The Blue Boy, for example, is an elaborate exercise in van Dyck style, with the sitter even dressed up in van Dyck costume. It is also a triumphant smack in the eye to Gainsborough’s great rival, his opposite in every respect, Joshua Reynolds, who had pronounced that blue could not be used in the main part of a picture.

It was probably the fact that Reynolds was kingpin in London that led Gainsborough to keep away from the city for the early part of his career, first basing himself in his native Suffolk and then living for sixteen years in Bath – as Hamilton puts it, ‘a king in exile’. But by the time The Blue Boy was painted in 1779, Gainsborough had been in London for five years, taking on Reynolds head to head. It meant that he also took on Reynolds’s power base, the Royal Academy, though he himself was a member. Reynolds, the Academy’s first president, was a master manipulator, so it should come as no surprise that Gainsborough suffered repeated frustrations there until, in 1783, he withdrew his pictures from the annual exhibition and instead showed them in his own house on Pall Mall. That building, Schomberg House, survives as telling testimony to the grandeur in which a successful artist could live in the 18th century. Hamilton’s book brings one of the very greatest of these vividly to life.