Until recently, they were unappreciated and undervalued, having slipped out of fashion with the advent of shampoo just before the war. Victorian women must have had hair as greasy as the fleeces of old sheep, but the ideal locks for binding down tiaras.
The items in this collection are not diamond encrusted and are to be auctioned in just five lots - an indication that the auctioneer David Lancaster expects dealers to be the biggest bidders, rather than glamourous young things seeking a tiara for a wedding, or a club night. He expects pounds 1,000-pounds 1,500 for a lot of 35 "antique-cut steel hair ornaments", some with hinged drops, worn on the bun, that would have swayed and sparkled at gas-lit balls. The cheapest lots, including specimens in tortoiseshell, coral, ivory and paste pearls, are estimated to go for pounds 600-pounds 800.
Tiaras are in the form of a complete circle: crescent shaped ones, sometimes attached to a comb, to anchor them - the majority in the sale - are strictly diadems.
But faulty nomenclature is a comparatively minor faux pas. Etiquette dating back to 1800, when they became popular, dictates that only married women may wear tiaras, because they symbolise the effulgence of Venus. At a wedding, the tiara is exposed only when the veil is raised.
No doubt the young women wearing tiaras and see-through dresses at the glittering blue glass and chrome club Legends in Mayfair (or dolled up at the Aquarium in Shoreditch or The Cross in Islington) have discovered less conventional ways of sacrificing to Venus. One bride, 30-year-old Michele O'Callaghan, who was married in a Dublin church this month, did without a veil because it did not suit her Amanda Wakeley ivory and charcoal dress but wore a tiara of moonstone flowers and diamante. "Attitudes have changed," she says, "tiaras are a modern accessory these days. I wanted one to jazz up the dress and create a sense of occasion - as tiaras do."
Geoffrey Munn, managing director of Wartski, the Queen's jeweller, whose "One Hundred Tiaras" exhibition in March helped to ignite the tiara boom, says, "Tiaras are the crowning glory of jewellery. Nothing gives more hauteur to the owner, nothing is more alluring, more flattering. In the 19th century they were the kit and caboodle of every woman from the middle class up."
Mr Munn is quick to dispel the misapprehension that only the nobility is allowed to wear them. "Anybody who buys a tiara is no less a tiara owner than the most noble." He warns of another faux pas. Do not wear your diadem with its base exposed. Twine the hair over it so that the sparklers seem to be springing from the head.
Many tiaras, he points out, come apart to make several brooches and a necklace. "You can have huge fun with these glittering bits of Mecanno." At the height of their fashion, during la belle epoque, up to three tiaras at a time might be worn.
Catwalk stars such as Kate Moss, Naomi Campbell, Christie Turlington and Linda Evangelista - as well as Madonna and the actress Kate Beckinsale - have all sported the witty creations of today's tyro of the tiara, the young jeweller Slim Barrett. John Galliano has commissioned Barrett, as have Katharine Hamnett, Claude Montana and John Rocha.
It was Barrett who designed the pounds 250,000 Celtic-motif tiara with yellow diamond drops and 6.9 carat yellow rondel that was the contemporary centrepiece of the Wartski exhibition.
It was admired by the Queen Mother, who lent her wedding tiara to the exhibition, and who attended that famous tiara-revival bash, the Marchioness of Dufferin and Ava's 90th birthday ball at Claridge's in January. Tiaras were stipulated. These days they are de rigueur only at the state opening of Parliament and state banquets. In Victorian times, "white tie" invitations always meant that tiaras should be worn.
The Americans are at last beginning to understand that tiaras can be worn by anyone. Barrett's wife and partner, Jules de Bairead, says that when Bennett first displayed a collection of his tiaras at the Plaza, New York seven years ago, the Americans scoffed. "Some were quite shocked. They thought we were trying to introduce the idea of English royalty." One had said mockingly to his wife: "Hey, wanna be a Princess for a night?"
The fact that tiaras are still undervalued is shown by the fact that dealers at auction buy the diamond ones to break up and sell as brooches or pendants. Tiaras are given only glancing references in jewellery textbooks. But Mr Munn is writing a book about them, and so is Britain's biggest collector of tiaras, Jen Cruse. Books tend to give collectors confidence and to push up prices.
So grab some tiaras cheaply, while you can, get your hairdresser to twine them into your hair - and tell him to forget the shampoo.
Christie's South Kensington, 85 Old Brompton Road, London SW7 (0171- 581 7611). Antique and collectable jewellery sale, Tuesday, 2pm.