For thirty-six years now, Sotheby's has been staging sales at the Gleneagles Hotel, in Auchterarder, Perthshire, tempting not only the Scots but also the sportsmen who flock to the North in pursuit of the stag, the salmon or the world's most famous eighteen holes. This year, the auction house is offering its characteristic mix of vintage and sporting guns (30 August), Wemyss ware and jewellery (31 August)--and probably its most impressive paintings sale ever, on 1 September, which is expected to realise around 4 million [pounds sterling]. At its core is a group of thirty-five paintings by Jack Vettriano (b. 1951), the hottest property in Scotland, and a cache of thirty works by Francis Campbell Boileau Cadell (1883-1937), widely regarded as the most versatile and accomplished of the Scottish Colourists.

The meteoric rise of Jack Vettriano is nothing short of phenomenal. This self-taught artist who left school at sixteen to work as a mining engineer in the local coalfields has become a popular cult hero, adored by the public if not always by the critics. His girlfriend gave him a box of watercolours for his twenty-first birthday, and the rest, as they say, is history. In 1989, he showed two paintings at the Royal Scottish Academy and sold both on the first day. The following year, three were snapped up at the Royal Academy Summer Exhibition. Since then, thanks not least to clever marketing by the Solstice Gallery in Edinburgh and the Portland Gallery in London, which saw his slick film-noir-ish images reproduced on greetings cards and posters--over 500,000 posters of his paintings have been sold worldwide--there have been sell-out solo shows in Edinburgh, London, Hong Kong and Johannesburg.

Two years ago at Gleneagles, Vettriano's The cafe was knocked down for a record 44,000 [pounds sterling], and records have tumbled ever since. At Sotheby's sale at Hopetoun House in Edinburgh this April, his most famous image, The singing butler, became the most expensive painting ever sold at auction in Scotland when it realised 744,800 [pounds sterling]. Little wonder, then, that this month's sale sees so many Vettrianos, most of which had probably been acquired for a few thousand pounds in the early 1990s, and are now conveniently packaged in a separate catalogue. Star billing goes to Mad dogs, probably the artist's best loved picture after The singing butler. It comes with an estimate of 200,000 [pounds sterling]-250,000 [pounds sterling]. There seems to be no sign yet of the Vettriano bubble bursting, though one wonders how successful an artist has to be before he or she stops playing the antiestablishment card.

To the delight of Sotheby's, Vettriano-mania has brought a number of new buyers through its doors in the past few years. Better still, some have also gone away with something else, too. This year's sale has something for most tastes and budgets, with the likes of John Duncan Fergusson's pencil study for Rose rhythm of 1916 estimated at just 1,000 [pounds sterling]-1,500 [pounds sterling]. But it is Fergusson's fellow Colourist Cadell who steals this particular show. Cadell steeped himself in French Impressionism as a student at the Academie Julien in Paris 1899-1902, and, during subsequent trips, in the intense, saturated Fauvist colours used by Matisse and Derain. Unlike Fergusson and Peploe, however, Cadell returned to Scotland and took to painting still-lifes and interiors, spending the summers painting landscapes on the island of Iona.

Dominating this sale is a large canvas of the gesuati in Venice, painted during a seminal trip to Venice in 1910 that led to an explosion of vivid, high-key colour (estimate 150,000 [pounds sterling]-200,000 [pounds sterling]). The white sofa, dated three years later, is a delicious Impressionistic exercise in loosely painted rich creamy whites and pastel hues (70,000 [pounds sterling]-100,000 [pounds sterling]). Most striking of all is The red chair, which epitomises a later group of more deliberate structured interiors with formal geometries and pure primary colour--but even here Cadell cannot resist the soft pools of reflected colour (100.000 [pounds sterling]-150,000 [pounds sterling]).

After the Great War, Cadell began painting on Iona using unprimed board which gives his pigment a more chalky consistency and an almost luminous quality, A characteristic view of Treshnish Point is offered here for 15.000 [pounds sterling] 20,000 [pounds sterling]. The market rarities, however, are sixteen pen and ink with watercolour wartime illustrations of Tom and Jack and their training camp antics--including playing football which display Cadell's deft and expressive economy of line. The group was bought through Alex Reid & Son in Glasgow by one of Cadell's most loyal patrons, Ion Harrison, and is now consigned to auction by his descendants.

Apart from Jack Vettriano, the Scottish artist who has seen the most dramatic price-change in recent years is Anne Redpath, the most significant Scottish artist of the fifties and sixties. Dominating the group here is her characteristic--and delectable A pale still life (estimate 30,000 [pounds sterling]-50,000 [pounds sterling]).