THE only known pair of rare oak dining chairs deigned by Charles Rennie Mackintosh are to go under the hammer this week.

The two chairs, dating from 1911 and valued at £10-15,000, were originally a set of six designed by Mackintosh for his friend, the decorator William Davidson.

The whereabouts of the other four is unknown.

The chairs will go up for auction in Edinburgh on Wednesday as part of auctioneer Lyon & Turnbull's sale of Decorative Arts.

John Mackie, Director and Head of Decorative Arts at Lyon & Turnbull said, "No one knows if the other four chairs form this set remains in existence, it would be wonderful if we could find them Mackintosh's' genius was that he had the ability to make something new out of tradition, as these deceptively simple chairs demonstrate. In common with, for example, his interpretations of ladder back chairs in various manifestations; Mackintosh has designed his own version of this vernacular chair. The back, typically squat, has been elongated, and the number of slats doubled from a characteristic four to eight. He has further accentuated the vertical character of the chair by omitting the cross-stretchers, normally found to the front and rear."