At once commonplace and magical, mirror possesses a magnetism irresistible to the human eye. Used in an interior, it has an unrivalled power of transformation, doubling and redoubling space, creating unreal vistas on to a world that is back to front but still the right way up. And, while mirror has been used to create some of the world's most extravagant rooms, including the Salle des Glaces at Versailles, Coco Chanel's Paris salon, Indian palaces and American casinos, thanks to modern methods of manufacture it is no more expensive than good wallpaper and no more difficult to install than tiling.
It wasn't always so. For centuries after its discovery in pre-Roman Egypt, mirrored glass could be produced only with great difficulty, and in very small sheets. Like the finest jewels, it was believed to hold mystic power. A reflection, it was thought, could capture the soul, hence mirrors were turned to the wall throughout illness and after death, until the soul was safely delivered. The chemical decay that attacked the silvering of old mirrors was blamed on moonbeams. Seventeenth-century Dutch housewives protected their mirrors with curtains in order to preserve their reflectiveness, lest it should run out through overuse. No wonder breaking a mirror was thought to bring seven years of misery.
In the late 17th century, sponsored by the French king's passion for mirrored walls, a method of casting molten glass and grinding it smooth was discovered so that, for the first time, a sheet of mirror large enough to reflect more than a head and shoulders could be produced. Mirrors like these were a phenomenon, a marvel, a new experience. The Salle des Glaces at Versailles still astounds with its scale and grandeur. How much more extraordinary it must have seemed when the mirror itself was a rare and extravagant commodity.
Methods of manufacture improved with small bursts of innovation throughout the 18th century. Robert Adam made extensive use of mirror, most notably for the "glass drawing-room" at Northumberland House in London, now long since demolished. By all accounts it was an astonishing room, with its walls of glass backed with a dark red pigment, punctuated by pier-glasses and overmantel, the whole linked and embellished with ornate metal fillets.
By the 19th century, large mirrors had sprouted over the mantel of every self-respecting parlour, bringing light to the darkest wall of the room and emphasising the central importance of the fireplace.
In the age before electric light, mirror continued to serve a practical as well as a decorative role, effectively doubling the light of candles and dim gas flames.
By Queen Victoria's death, mirror had been democratised. Brilliant-cut for extra sparkle, mirrors were adopted by the fairground, the pub, the Gypsy caravan and the long-boat.
The ability to make glass in large sheets has had a profound effect on the history of architecture, famously described by Le Corbusier as the battle of the window to attain the greatest dimensions in the face of technical limitations. Today that battle has been decisively won.
Modern plate glass is floated on molten tin, minimising the need for the grinding and polishing that made old mirror so labour-intensive. In 1937, architects Raymond McGrath and AC Frost wrote a book entitled Glass in Architecture and Decoration, a paean to the new possibilities allowed by this "medium capable of endless adaptation without loss of integrity". Some of that period's most important interiors, inspired by what the authors describe as "the recent purge or spring-cleaning of architecture and design" use mirror in a way that still looks up-to-date; the fashionable interior decorator Syrie Maugham's all-white drawing-room with its chrome- and-mirror screen; the film star Tilly Losch's mirrored bathroom; Norman Hartnell's mirror-panelled salon.
Mirror's recent image has suffered from its ubiquity. As a cheap means of invoking glamour it is too often used indiscriminately in restaurants, cinema foyers and hotels. The horrible Seventies vogue for bronzed mirror glass; the smutty connotations of mirrored ceilings; the popularity of mirrored fitted wardrobes - all have further contributed to the suspicion that mirror, as opposed to the venerable looking-glass, is rather vulgar.
This is unfair. Poor design makes mirror look nasty but, used well, it can still delight and transform. David Hicks was a master, and used it to enhance the sense of space and grandeur in his own, small Albany apartment. Other decorators have made much of it: Michael Inchbald mirrored opposing walls in his hall to give the illusion of endless vistas punctuated by an ever-diminishing file of reflected obelisks; Frederic Mechiche lined a stairwell with it; David Gill used it to line his bathroom. Charles Jencks, like Sir John Soane before him, used jewel-like fragments of mirror inlay to highlight his architectural fantasies.
At this year's House & Garden Fair in Earl's Court, of four room-sets given pride of place at the centre of the Great Hall, three featured mirror.
Emily Todhunter's included a bath panelled in mirror, a mirrored chest of drawers and a mirrored coffee-table. Just across the aisle, Alidad's circular "gentleman's cabinet" was entirely panelled with mirror glass that had been distressed and decorated for an effect utterly different from the clarity of Todhunter's style. Most hip of all, Jonathan Reed used two large mirrors, one of them an antique convex mirror the size of a luxury car wheel, the other a simple oblong, plainly framed in wood.
Once, the cost of the glass itself vied with the price of the most elaborate frame. Today a frame of real quality, old or new, remains very costly, but mirror glass is cheap, DIY superstores sell an array of unframed mirrors, round, square, large and small, some bevelled and most under pounds 30. They also sell mirror tiles in different sizes.
Every town has a glazier. Here you can order mirror cut to size and, within reason, shape. And now the fun begins. Stained coffee table? Cover it with mirror, bevelled at the edges. Soon you will find yourself arranging pebbles or candles or even ash-trays, and marvelling at the effect. Dreary fireplace? Tile it with mirror. Dark basement? Mirror the window sills, or better still the whole embrasure. The increase in light is dramatic.
Interior bathroom with no window? Mirror a wall and the sense of claustrophobia almost disappears, And if the sight of yourself, rubicund and wobbly, fresh from a hot shower is too much to bear, you needn't rely on the misting effect alone. Brutally honest modern mirror can be "antiqued" for a more flattering reflection.
As a cure for lack of light and space, mirror requires little training or expertise to administer. As a material in itself, mirror glass has no particular style allegiances. Mirror is as appropriate in a modern loft as in a Regency rectory; its effect can be luxurious or sober, sparkling or mined, extravagant or spare.
Play with it, experiment, be brave. It won't cost you an arm and a leg. Just try not to break it; no one deserves seven years of bad luck.