These are the people Sargent painted in his swagger portraits: the very rich who so publicly flourished in what J Mordaunt Crook calls the "age of ostentation". This lasted from the digging of the Kimberley diamond mines in the 1870s to the Great Crash of 1929. Like the poor, Crook says, "the nouveaux riches are always with us". But in those years they were more showily with us than at any time before or since, except perhaps in the glittery 1980s.
They were, for a start, obsessed with building themselves palaces, castles and mansions. The offices where they made their money might be bleak sheds, but their homes were a riot of gilt, marble and bronze. In the 1980s, contrariwise, it was the offices, flashily postmodernised, that got the treatment. Crook's subtitle is Style and status in Victorian and Edwardian architecture, but The Rise of the Nouveaux Riches is really a social and economic history - a kind of onyx bookend, to be paired with David Cannadine's The Decline and Fall of the British Aristocracy.
Lawrence Stone, the assiduous historian of the family, has complained that the map of English social history is full of huge blank spaces, more often than not labelled "here be the rich". Here is one corner shaded in with great scholarship. And if Crook, professor of the history of architecture at London University, is largely chronicling a dead society, he dances very enjoyably on its marble-angeled grave. He has an eye for the deadpan quotation. Of one upstart in these years, it was said that "in the dead silence of the night you can hear a distant but monotonous sound - Sir Gilbert Parker, climbing, climbing, climbing". When Philip Sassoon died, surrounded by the highest of high camp design, his friends remembered, in all fairness, that "his baroque was worse than his bite".
The architecture was not, generally, top notch. The millionaires who made their own money the hard way put their genius into business, not into style. They hired men who would run up the environment they wanted, like a fashionable tailor. From the politicians, similarly, they hired baronetcies and peerages. Sometimes it was only the title that lasted. "First the money, then the land, then the champagne," is how Crook puts it.
Clogs to clogs in three generations. One railway king, building himself a new mansion, put a single pair of clogs on display in a glass case, as a talisman against excessive pride. Looking up the latest scion of one nouveau lineage, I found him listed as living in a suburban cul-de-sac, practising as a marital and sexual therapist.
The money came from all over the place but, before New York's supremacy, it all came to London. Sometimes it came from booming Britain: soap supremos (William Lever), malted-milk moguls (James Horlick), princes of pills (Joseph Beecham). James Morrison, draper, even made a multimillion fortune out of black funeral crepe. Sometimes it came in from the US, eased by the "gilded prostitution" of heiresses such as Consuelo Vanderbilt (grandmother of Winston Churchill - and painted by Sargent), who was married off to the decaying dukedom of Marlborough. William Astor said, "America is no place for gentlemen". He then emigrated. His American enemies said that he was just shifting to the land of "lust and baccarat".
But much of the time the money came from the outposts of empire. From south China came the riches of men such as William Jardine (known in Canton as "the iron-headed rat"), who prospered out of the opium trade. Most often of all there was South Africa. Without its attendant gold and diamonds, plutocracy would have lost its sheen. When Beatrice Webb dined with the Wernhers at Luton Hoo she was dismayed by the contrast between the lavishness of the mansion - fitted out by the architects of the Ritz - and the squalor of the lives of the inhabitants of pre- Vauxhall Luton, beyond the gates.
Julius Wernher made his money in South Africa and he was a Jew. Jewish wealth runs through Crook's pages like a golden thread. It is entwined with the black thread of anti-Semitism. When Edward VII, as a new king, visited Aldershot, they shouted at him: "King of the Jews." Anthony Trollope's fraudulent financier Melmotte, in The Way We Live Now, was based on Baron Grant (born Gottheimer), who built the largest private house in London, in Kensington Palace Gardens, though the money ran out before it was finished. The marble staircase is now in Madame Tussaud's. Barney Barnato, a music-hall turn from Whitechapel who made millions from diamonds, drowned mysteriously at sea, as did Robert Maxwell. Much more durably, there were the Rothschilds, the Goldsmids, the Cassels, the Sassoons.
Ostentation paid the price of envy. "And there was substance in this popular suspicion," Crook notes, with a historian's punctiliousness. On the eve of the first world war more than a fifth of all non-landed millionaires were Jewish, though only 3 per cent of London's population (and 0.3 per cent of Britain's) were Jews. "I shall not want capital in Heaven," T S Eliot wrote, in a stanza no longer in the dictionaries of quotations, "For I shall meet Sir Alfred Mond./We two shall lie together, lapt/In a five per cent Exchequer bond." Ethnic minorities have to tread gently. They are damned if they don't prosper, and damned if they do.
Sometimes, in Crook's pages, you feel lapt in summaries of Burke's Peerage or Who Was Who. But mostly he tells a story that fixes you with a horrified fascination. The wine, it seemed, would never stop flowing in Park Lane, London's own Fifth Avenue. The butlers, footmen, maids and under-maids would never stop scurrying. In the country houses the weekend parties would apparently never cease.
But they did. In 1939, Philip Sassoon died. A lone aircraft scattered his ashes over his parkland. "Take down the Union flag," he had once said; "it clashes with the sunset." Capitalism knows no homeland.