Spending: Much sought after by swinging cats: Collectors of 20th-century designer furniture can snap up bargains at an auction if they know what to look for, says John Windsor

CATCHING sight of my chromium hanging cage chair, bought for pounds 40 in a Hackney junk shop, a guest of mine curled his lip and said: 'Oh, yes, very Sixties.' It is a pity he is no longer welcome in my home. I could have bragged to him that the same model carries an estimate of pounds 500- pounds 700 in Bonhams Knightsbridge sale of 20th-century furniture and design next Saturday (2pm).

I learnt from Alastair Nicolson of Bonhams that it is a Parrot Chair, a classic design launched in 1974 (not the Sixties) by Abre Designs of Sweden. This information met with a yawn from Piglet, my big white cat. Unimpressed by Mr Nicolson's research - sourcing the chair to the exhibition 'Classic Plastic, A Look At Design 1950-1974' at Fischer Fine Art in London four years ago - Piglet cares only for the chair's curl-up- and-snooze quotient.

Collectors of 20th-century designer furniture, on the other hand (the period is now reckoned to span 1930-1980), amass whole libraries of design magazines, guidebooks, manufacturers' trade catalogues and exhibition catalogues published by museums and galleries.

You need an educated eye to distinguish modernistic high street tat from original designer furniture. Most established manufacturers happily emblazon each piece with their name or that of the designer. With no name visible and no trace in the guidebooks, beware. Seasoned furniture buffs can tell whether a cone-shaped stool by the exotic Danish designer Verner Panton is an original manufactured in 1959 by the design's first licensee, Plus-linje (circular feet in clear plastic), or a later version by Fritz Hansen (rectangular black plastic feet).

Like other markets for second-hand household goods, 20th-century furniture is divided between collectors and furnishers. Collectors look for museum- worthy originals (about 25 per cent of bidders are from institutions such as design museums). Furnishers, who care about as much as Piglet does whether a piece has clear circular or black rectangular feet, are after classic but home- worthy designs at knock-down prices.

Whether or not you are a purist collector, at least find out whether a piece is still in production. If it is, then the estimate in the auction catalogue is likely to be as little as a quarter of its high street price and bidding is likely to stop at half the high street price. Why pay more?

If production has ceased, creating rarity value, the estimate is still likely to be less than the last available indexed-up retail price - but furnishers should avoid being drawn into a saleroom battle between collectors.

An example of in-production auction prices: at Bonhams last year, six welded steel wire-mesh side chairs with black upholstered seat pads, a classic design by the American Harry Bertoia, first manufactured in 1951, were estimated at pounds 180- pounds 220, under a quarter of their current retail price of perhaps pounds 800- pounds 1,200. At the sale the bidding was pushed to pounds 440. No matter whether collectors were attracted by some 'original finish', apparent only to themselves, the price was still only a third to a half of the retail price.

As for saleroom battles, last year two collectors took a fancy to a pair of 1960 'Champagne' chairs by the Americans Erwine and Estelle Laverne - Perspex on aluminium swivel bases, from a series lovingly recorded in the guidebook Modern Furniture Classics Since 1945, and exhibited by the Philadelphia Museum of Art in 1983. They pushed the pounds 550- pounds 650 estimate to pounds 2,090.

Contemporary furniture, especially in plastic, tends to be hard wearing. So the trick of buying good furniture at auction, giving it light wear for four or five years, then getting back close to the same price at the same auction house applies as much to 20th-century furniture as to antique. One second-time-around lot at Bonhams next Saturday is 'Jan', a 1970 blue upholstered reclining chair and ottoman by the Swede Jan Ekselius. Jan fetched pounds 506 last year (est pounds 550- pounds 750). This time it is estimated pounds 450- pounds 650.

The eclectic householder may be surprised to find how good classic contemporary furniture can look in old houses. Friends of Mr Nicolson live in a Georgian crescent in Bath and their house contains an Arne Jacobsen ant chair and an Eero Saarinen pedestal chair. The secret, some say, is to slap around a lot of white on walls and ceiling. In my 1864 terraced house, the Parrot Chair lives in a white-painted, architect-designed rear extension that, in the opinion of visitors, is no greater affront to the existing architecture than the chair itself.

For the newcomer in the classic furniture market, whether modern or antique, a good rule of thumb is to select furniture that is architect-designed or at least architect-inspired. Victorian furniture inspired by Pugin or designed, for example, by the architects Alexander Jackson Davis or James Renwick Jnr is rising steadily in value. So is furniture designed by Charles Rennie Mackintosh and Frank Lloyd Wright.

Architects are also the biggest names in 20th-century furniture design. The most celebrated is Alvar Aalto (1898- 1976), Finland's greatest modern architect. Of comparable status are two post- war names: the American Charles Eames and the Finn/American Eero Saarinen. They studied (as did Bertoia) at the Cranbrook Academy of Art in Bloomfields, Michigan, probably the most influential American art and design school during the inter-war years, sometimes nicknamed the American Bauhaus. Tutors and graduates from the Cranbrook dominated two American furniture manufacturing giants, Herman Miller and Knoll International (whose trade catalogues are a must for the collector).

Eames and his wife, Ray, are known for their characteristically American moulded plywood and chromium dining chairs and fibreglass shell chairs, which are built on Scandinavian technology. Two Forties Eames plywood and chromium dining chairs manufactured by Miller are estimated pounds 250- pounds 350 and pounds 300- pounds 400 at Bonhams. The design is now so imitated that these must be considered collectors' rather than furnishers' prices.

The other famous Eames chair is the original recliner, the '670' lounge chair in moulded plywood and leather upholstery of the Fifties, also originally made by Miller. Bonhams is offering five, one in brown leather with ottoman at pounds 500- pounds 600, three without ottoman but in more desirable black, pounds 450- pounds 600, and a fifth, brown without ottoman, pounds 400- pounds 500. The high street price for the Eames 670 (now made by the German Vitra company), is pounds 2,328 including ottoman. Bonhams' is definitely a furnishers' estimate.

Besides Fifties Scandinavian and post- war American, innovative Sixties Italian designer furniture is highly collectable. The Italian Joe Colombo produced a timeless bent wood armchair in 1964 that is estimated at pounds 500- pounds 700 and comes complete with sale catalogue pedigree - Museum of Modern Art, New York, the 1991 Fischer exhibition Pioneers of Modern Furniture, etc. Among the eight Colombo lots is his own contribution to lounge chair evolution, the black leather Elda of 1963 with rotating cylindrical base, est pounds 400- pounds 600. For the collector of Italian furniture, back-numbers of the Italian magazine Domus are an important source.

Source literature in print: Modern Furniture Classics Since 1945, by Charlotte and Peter Fiell (Thames and Hudson, pounds 28). Sourcebook of Modern Furniture, by Jerryll Habegger and Joseph H Osman (Van Nostrand Reinhold, New York, pounds 23.50). Contemporary Furniture, edited by Klaus-Jurgen Sembach, (Design Council, pounds 18).

Out of print: Modern Furniture Classics, by Miriam Stimpson (Architectural Press, 1987, paperback pounds 9.95). Furniture Designed by Architects, by Marian Page (Architectural Press, 1983, paperback pounds 10.50).

(Photograph omitted)