Is there a Caravaggio in the house?

The setting is awesome: a high-ceilinged hall filled with paintings and echoing footsteps. Voices sotto-voce. A single table is set up in one corner with a brilliant light beamed onto it.

We sit on the mock-marble bench like courtiers waiting for an audience, me with my tell-tale notebook but everyone else with packets mysteriously wrapped in brown paper or - more professionally - in bubble plastic. At 10.30 a.m., Hilary Pyle and Adrian le Harivel, curators of the Yeats and of the British and Irish Collection respectively, enter the Shaw Room of the National Gallery in Dublin to begin the monthly Picture Clinic. Brown paper rustles, string is untied, pictures are unwrapped and finally placed on the floodlit table for appraisal. It's an anxious moment, though nobody, of course, displays too much emotion. After all, these pictures have been hanging on walls, propped up in attics, packed away in back bedrooms for so long that their presence has been taken for granted.

Now, however, they're being exposed to a world outside the family home, to be examined by the cool eye of an art expert, assisted by an all-seeing magnifying glass.

Hilary Pyle bends over an oil painting. Adrian le Harivel turns away to consult one of his reference books. Together they look again. Breathless, we wait for the verdict. A Caravaggio, perhaps? But no. Sergio Benedetti, the Gallery's Chief Curator, has already done that one.

Hilary Pyle smiles kindly: "It's a charming painting," she says and then, being an expert, goes on to educate us a little about the painting's weaknesses: the careless finishing off of the cloak, the absence of detail in the face, the flatness of the background. She makes a few suggestions - perhaps a different frame, or one of a different colour? A sprinkling of dealers come each month for an opinion or because they want their own suspicions confirmed by the gallery. The majority of people who come to the gallery's clinics, however, bring along pictures that have been in the family for years. Perhaps they're moving house or their elderly mother is thinking of tidying things up, making a will, deciding what to leave to whom.

An appraisal is always useful - just in case. But, unlike the popular TV Antiques Road Show, the gallery curators never ever give an evaluation: "We are obliged by the Government not to do that. Instead, we provide an appraisal service to the public," says Valerie Keogh, from the gallery's PR department.

People come from all over Ireland and from both sides of the Border, with prints, etchings, paintings and drawings. There are five curators at the gallery and though they rotate their duties they may, if it is needed, seek the advice of a colleague whose field of expertise is different from theirs.

Dubliner Finbarr Wall went away enriched if not made richer by his morning at the clinic. With his wife, he had brought along an oil painting that had been a wedding gift to his mother from her Belfast father. The painting was an Annunciation scene. (Clue: the lily.) Encircled by a frame splendidly ornate and bright gold in colour, probably Florentine in origin, the painting proved also to be Italian. The frame, Hilary Pyle pointed out, had suffered from being regilded perhaps a bit too enthusiastically and therefore outshone the painting itself. A dulling down would be in order. It had probably been brought into Ireland, from Italy, some time after Catholic Emancipation, we were told. We looked down at the gift Finbarr's grandfather had made to his mother and saw a part of his family's history intertwined with that of Ireland's own. It was a morning well spent.

The National Gallery's appraisal service is available to the public on the first Thursday of every month, from 10.30 a.m. to noon. The service is free.