As a result of her technique we are not only reminded that photographs should not be mistaken for reality, but we also see how all matter is vulnerable to the effects of time.When, in 1995, Yass undertook a project to document the doctors and patients at Springfield Psychiatric Hospital, she found herself confronted with an ethical dilemma. The people in them are described not by their names but by their job titles, that is by their positions within the hierarchy of the art world. More strikingly her signature blue seeps into every component of the image including the sitters themselves.If having your photograph taken is generally thought to memorialise and reaffirm you, then the way Yass approaches her subjects has a distinctly corrosive effect on their identities. Executed in an unsentimental manner, the pictures do not encourage personality to shine through. Gallery directors, fellow artists, heads of companies, even the entire selection committee for the Arts Council of England, all passed before her lens.Needless to say the results have little in common with standard photographic portraiture. She makes her work by taking two photographs of the same subject one directly after the other on a large format plate camera The first is shot on normal transparency film.

The second is taken on the same film and processed as a negative, which has the effect of turning everything blue. The two are sandwiched together and from this composite a finished piece is created which is subsequently mounted on a light box.When she left Goldsmiths' Yass found herself spending so much time approaching galleries and businesses in an effort to get herself exhibited that she decided to make the people who wielded the power in these institutions the subject of her photographs. Brighter areas turn a vivid, almost impenetrable blue and occasionally lines of sharp white light intervene at points where different elements of the composition meet. Yass, 36, studied at the Slade before going on to Goldsmiths' where she did her MA. Like the pictures of Baden-Baden, the colours in these depictions of "contained male spaces" are wildly distorted. The prestigious Glen Dimplex Artists' Award, worth pounds 15,000 and open to anyone who has exhibited in Ireland in the past year, was presented to her for a series of sumptuous photographs of empty urinals and unoccupied capsule hotel rooms for Japanese salarymen in Tokyo. Five months on and Catherine Yass - whose works had lit up that dark winter night - has just scooped the Irish equivalent of the Turner Prize. But while my immediate surroundings - all peeling paint and chipped tiles - bore the unmistakable stamp of verite, the pictures on the walls were like windows onto another world.

Glowing in feasible shades of yellow, green and aquamarine, these were not your typical photographs. Instead they were closer to hallucinations hovering somewhere between history and dreams. Above me eight illuminated photographs cast their fluorescent light over the place. Mirroring the spot where I stood, they were of empty 19th century bath-houses in the German spa town, Baden-Baden. One evening last February I found myself standing in a disused swimming pool 50ft beneath Tottenham Court Road. But there is no good evidence that French mothers are better fed than their British counterparts.So I shall continue to drink my malt whisky, and take miniatures to dinners where only wine is served.