This year, a twin set of fountain pens called Peter and Catherine the Great is retailing for pounds 1,300. By the end of the year it will be selling at Bonhams, the London auctioneers, for pounds 1,600-pounds 1,800.
There are three reasons for the premium value: the twin set is by Montblanc, German makers of the world's best-known brand of quality pens: supply is limited to 4,810 (Mont Blanc's height in metres): such special editions are annual, making them a must for fountain pen collectors wanting complete runs (this happens to be the first twin).
When, as recently as 1992, Montblanc issued its first limited edition pen, the Lorenzo de Medici, knowledgeable collectors snapped it up, sensing correctly that they were in at the start of something lucrative. At auction, even in its first year, the splendid pen sustained its pounds 850 retail price and the year after was fetching pounds 1,100 - a sign that the time taken for some contemporary collectables to acquire added value was shortening drastically.
They are now worth pounds 3,000 mint and boxed in factory condition - a 350 per cent increase in five years. Subsequent Montblanc annual limited editions have earned more modest premiums but are still nice little earners: the Octavian of 1993, also pounds 850 retail, commands pounds 1,500-pounds 2,000 at auction, and is still a good investment.
Pitfalls for speculators: uneven allocation by fountain pen manufacturers, leading to premium prices in some countries and discounting in others.
Investment tip: Dunhill's first limited edition pen, the Namiki, with lacquer designs hand-painted by named Japanese artists, issued last year in four editions of 200, prices pounds 820 to pounds 5,200 for a special in powdered gold. Dunhill's original Namikis of the Thirties can fetch over pounds 5,000 at auction.
Sheer quality can yield instant profit. How's your literary discernment, for instance? In the past decade, auction prices for mint-condition first editions complete with dustwrapper of John Fowles's The French Lieutenant's Woman have dropped by half from their peak pounds 400-pounds 500.
Critical consensus has hoicked the dealers' price of first editions of Irving Walsh's 1994 paperback Trainspotting - only about 1,000 were printed - to pounds 500 from its retail price of pounds 4.99. Six months ago, before its Oscar- winning film debut, Michael Ondaatje's novel The English Patient, could be had for pounds 25. Now it is pounds 300. Original retail price in 1992: pounds 14.99.
Tip from Joanna Herald, a partner in the Ulysses bookshop in Museum Street, central London: Silk by Alessandro Baricco, published by Harvill Press, still in print at pounds 9.99 hardback, pounds 6.99 paperback. Her recommendation is based entirely on literary merit.
When you consider that book collectors of the Twenties and Thirties went barmy over first editions of Galsworthy (there's nothing new in first- edition speculation), you might consider that "take the money and run" is the best strategy in those limited-edition markets in which taste is volatile.
An example is the Swatch market, deliberately exploited by its cunning and humorous creator, Nicolas Hayek. He conducts a world-wide battle of wits in which collectors' and dealers' faxes, telephones and Internet modems throb with the latest rumours about rare, just-issued design variants worth tens of thousands of pounds, and Hayek's capricious allocations of "specials" that rocket or plummet in value in different countries.
Joseph Falcone, who trades in Swatches from his shop in the Meridien Hotel, Piccadilly, London, tells the cautionary tale of a Scot who fought his way through the scrum at Harrods' sell-out launch of the Swatch Christmas special "Roi Soleil" in 1993, having heard that the limited allocation would instantly be worth big money. He bought two for pounds 45 each and was gratified to see them changing hands for pounds 150 minutes before leaving the store. He did not know that, oddly enough, the Swatch shop in Oxford Street still had plenty for sale - at pounds 45.
Six months later, when Mr Falcone offered him pounds 75 each for his two, he reported he had sold them for pounds 60 each, the best price he could get. His trip from Scotland with his girlfriend had cost him pounds 600. Dealers now sell Roi Soleils for pounds 185-pounds 200. The trade price is pounds 100.
On the other hand, a Swatch collector holidaying in Madrid paid a mere pounds 10 for a mint and boxed 1987 "Puff" - one of only 120 made, with blow- away rabbit fur around the dial - having spotted it in a cardboard box in a shop. He sold it that year, 1993, for pounds 18,500. Puffs now sell for pounds 20,000-pounds 25,000. Moral: to play the Swatch market, do lots of homework.
Records and CDs, by comparison, are child's play. John Reed, research editor of Record Collector magazine, which publishes the biennial Rare Record Price Guide (pounds 19.95), recommends buying into indie groups' records. Their small-circulation "lo-fi" records turned out in bedrooms on four- track recorders are not sold by the big retailers and can rapidly acquire rarity value.
Lee Phelps, co-manager of Energy, mail-order record and CD dealers of Looe, Cornwall, is selling for pounds 50 copies of Baby Bird's CD, I Was Born A Man - issued only 18 months ago. Spice Girls? Their limited edition second CD of last August, with fancy fold-out, which retailed at pounds 3.99, is worth pounds 20.
Packs of glossy trading cards showing film stars and sportsmen include sparsely distributed "chase" cards that instantly acquire street value. Like Swatches, they are an example of managed rarity. A 3D double-size Pamela Anderson "case topper" card - one per case of 360 packs - is worth pounds 50-pounds 60 to collectors.
Most poignant case topper, according to the publisher-importer Barry Roness: personally signed Playboy cards of Ernest Hemingway's granddaughter Margaux Hemingway, model and actress. She was found dead in Los Angeles last July after suffering from bulimia and alcoholism. The card has become a cult collectable. Now worth $500, it is expected to be changing hands for $2,000 in a year's time.
You can easily discover which brand-new classic cars can be sold for instant profit by comparing newspaper car ad prices with manufacturers' list prices. The new Mercedes-Benz SLK, for example, which retails for pounds 30,090, immediately commands a secondhand price of pounds 40,000. The snag is that to get one you have to join the two-year waiting list that is responsible for the inflated price. What price an SLK in two years?
Bonhams' next fountain pen sale, 9 May (11am). Montblanc 0181-232 3000: Alfred Dunhill 0171-290 8600: Ulysses 0171-831 1600: Barry Roness 0181- 871 2997: Record Collector 0181-579 1082: Lee Phelps, Energy 01503-265515.