Can you tell an Artuqid jug from an Irnik pot? London's bi-annual Islamic week gives you the chance to try
Twice a year, in April and October, London becomes the world centre for Islamic artworks. Iranian dealers fill the salerooms. Any Anglo-Saxons are likely to be sellers, perhaps eager to see whether the loathed Persian ewer left to them by granny will raise the price of a Caribbean holiday.

A few Americans, Germans and Swiss also bid, some affecting to understand the tangled Arabic calligraphy that so eloquently mimics the peaks and troughs of an unpredictable and exasperating market.

Buy for decoration - inlaid Islamic furniture looks good in any room - or do some homework first. Even the western "experts" who mount these auctions regularly blunder, failing to spot fakes or getting estimates hopelessly wrong.

The big auctioneers, Christie's and Sotheby's, are often left with half their goods unsold while the price of the occasional "sleeper" goes through the roof. At Sotheby's last sale, in April, a magnificent 14th century gold inlaid spherical jug from northern Syria, bearing the name of a sultan of the Artuqid dynasty, was estimated at pounds 10,000-pounds 15,000 - and sold for pounds 128,000. But it was among only 17 of the sale's first 60 lots - mainly early Persian pottery and metalware - that found buyers. Sotheby's had estimated the 9th-13th century wares at pounds 2,000-pounds 3,000 or more each, despite a glut of fresh finds exported through Afghanistan that had reduced their value tenfold.

London's most go-ahead Islamic auctioneer is Bonhams whose expert, Diddi Malek, is a half-Persian, half-English Muslim who speaks and reads Arabic, hobnobs with Middle-Eastern buyers and sellers, and has in three years raised her totals to over pounds 400,000 a sale. She has teamed up with Hamid Atighetchi, an Iranian consultant in Islamic art based in London.

Be aware also of the cultural slots that bidding falls into. The westernised Turks buy Turkish goods but tend to ignore even their own Iznik pottery if it bears Islamic calligraphy. By contrast, Iranians seeking out work from the 16th century height of Islamic art are not concerned whether it is Turkish or Persian.

Among Islamic artworks closest to British cultural and polical history is Indian Mughal jewellery. Bonhams' sale, which has an eclectic selection of paintings, carpets, weapons, jewellery and manuscripts, as well as pottery and metalware, includes a handsome Victorian Indian Mughal gold and silver-gilt necklace with rubies, white sapphires and an emerald pendant: est pounds 400-pounds 450.

Bonhams (0171-351 7111): Tuesday, carpets (2pm); Wednesday, Islamic art (11am). Sotheby's (0171-493 8080): Wednesday, manuscripts (10.30am) and carpets (2pm); Thursday, Islamic art (10.30am) and Indian art (2.30pm); Friday, collonades (10.30am & 2.30pm). Christie's (0171-839 9060): Tuesday, manuscripts & miniatures (11.30am) and Islamic art (2.30pm); Thursday, carpets (2.30pm).