Collect to Invest: Museums and Americans are snapping up classic photographs, warns John Windsor
It may seem an unlikely comparison, but vintage photographs are a bit like Italian primitive paintings. There was a time when such paintings could be collected in armfuls. Then they were all gone.

The international market for photographs is still young, dating only from the mid Seventies. But scarce prints are fast disappearing into museums and the collections of rich Americans. The last chance to snap them up is now.

The blockbuster prices are for 20th century photographs. Collect historic 19th century prints if you must. But twentieth century prices are rising fastest and the market's preferences for names and images have not altered much over the past few years.

This makes investment simpler - although the range of quality, from numbered and signed "lifetime" editions to "later printings", run off by goodness knows whom, goodness knows when, is a perpetual nightmare for those lacking an eye for the subtleties of tone.

Front runners, price-wise, are Stieglitz, Kertesz and Man Ray.

The American Alfred Stieglitz (1864-1946) pioneered a direct, truthful "pure photography" and set standards of technical excellence, especially in portraiture. His portrait of the hands of his companion and inspiration, Georgia O'Keeffe - one of nine known prints, seven in museums and one in private hands - set a world record for a photograph of $398,500 (pounds 250,000) at Christie's New York that has lasted since 1993.

Andre Kertesz (1894-1985), a Hungarian, emigrated to the United States in the Thirties, where he photographed for Vogue and Harper's Bazaar. Last year his photograph of Mondrian's pipe and glasses fetched $376,500 at Christie's New York.

Five of the top 10 auction prices for photographs are for the work of the American Man Ray (1890-1976), who lived among the surrealists of Paris for most of his life.

There is solid demand for these top three, whose work is sold almost exclusively in New York. Even the second string - Edward Weston, Alexander Rodchenko and Edward Steichen - can fetch over $100,000.

Buyers in London should consider the favourite images of Bill Brandt (1904-1983), who was briefly Man Ray's assistant and went on to document British life with a surreal eye. There is a rising demand for characteristic images of his, such as his untitled nude of 1952.

One "printed later" is estimated pounds 2,000-pounds 3,000 in Sotheby's London sale next Thursday (10.30am). Another later printing of the same image made $2,860 (pounds 1,790) at Christie's New York in 1990. In 1986, Sotheby's sold one of unspecified printing for a mere pounds 770.

Nobody knows how many copies of the nude were printed. They are hardy perennials at auction, but repeated exposure seems to be making them more and more famous and boosting their value.

The same investment principle applies to other well-known images, such as Brandt's picture of a disgruntled parlour maid and under-parlourmaid about to serve dinner in 1933, which sells for around pounds 5,000, and the legendary French photographer Henri Cartier-Bresson's portrait, Rue Mouffetard, showing a boy proudly carrying home two bottles of wine, in Paris in 1958, worth around pounds 3,500.

Few 19th century images have acquired such a valuable cachet. Among the exceptions is Robert Howlett's stunning portrait of Brunel standing in front of the launching chains of the Great Eastern in 1857. Sotheby's expects pounds 1,000-pounds 1,500 for a copy in Thursday's sale. The print lacks tonal range. The astonishing pounds 22,000 paid for the same image in 1987 demonstrates the importance of condition.

The numbering and signing of editions may seem to be a reliable way of determining rarity value. But Sotheby's expects only pounds 400-pounds 600 for one of an edition of 10 signed prints of Bob Carlos Clarke's fetishistic nude "Nadia/Black Rope" (1991), whereas Robert Frank's "Chicago" (1955-57) - not a limited edition but known to be a rarity - is estimated pounds 3,000- pounds 5,000.

Sotheby's photographs, Thursday (10.30am), 34-35 New Bond Street, London W1 (0171-293 5000). Christie's South Kensington, fine and rare photographs, Friday (11am), 85 Old Brompton Road, London SW7 (0171-581 7611).