A dry or wet face-lift is at issue when it comes to sprucing-up Florence'sDavid for his 500th birthday, writes Patricia Leahy

August 1503: It was to be another year before Michelangelo would finish David. He had already been working on it for two years. Although the two tonne block was still surrounded by scaffolding, most of the form would have emerged from the stone. To finish it, he would need months of polishing and rubbing oils repeatedly into the marble until it was as smooth as skin.

The "Giant", as it was popularly known, was positioned in the open air at the front of the Palazzo Vecchio in September 1504. Not long afterwards, the left arm was snapped off during a riot in 1527. The white mixture of lime and sand used to reattach it is still visible. After absorbing the soot and rain for over three centuries, two botched 19th-century cleaning jobs were carried out on the statue.

In 1873, he was finally brought inside to the main hall of the Galleria dell'Accademia where he still remains, not altogether undisturbed. Around 12 years ago an unbalanced man took a hammer and knocked off the second toe on the left foot. A new toe was shaped from marble and plaster and reattached.

Now, approaching David's 500th anniversary, an international controversy going on for some years is heating up on what is to be done - or indeed, not to be done - to clean the grime from the statue. Since David had stood outside for so long, his pores are open and dust has accumulated in the marble.

Here is where the problem lies. The crux of the cleaning dispute concerns the method of restoration to be used. The "dry" one involves a slow, methodical use of chamois cloth, soft brushes, cotton swabs and an eraser. This has been used before, notably on another Michelangelo statue, the Moses in the tomb of Julius II.

However, the difference is that David has been exposed to the elements and has endured more weathering and erosion, thus more restoration attempts than Moses, over the centuries.

Opponents to the "dry" method say the greatest threat to the marble is gypsum, a calcium sulphate that responds to humidity which would eventually destroy the marble. They propose the application of "wet" poultices using distilled water which, they say, would also draw the dust out of the pores.

Already one experienced restorer resigned in April, saying the "wet" method approved by Florence's art establishment was too harsh and could cause damage. It could also affect the intrinsic colour variation in the marble, caused by natural veining as well as from chisel marks which crush the marble. This would give David an unnaturally uniform consistency.

Meanwhile, a petition, signed by 39 international artists and scholars proposes suspending action, pending a review by an independent commission of experts.

The leading art experts in Florence, who will have the final say, are playing down differences between the methods, saying they are both gentle and very light. They insist it is not the serious problem of conservation which concerns them and that it's only one of superficial cleaning.

The streaks and blotches of David's venerable old age will, or perhaps will not, shortly disappear. However, this sturdy masterpiece to the beauty of youth which has held a place in man's collective psyche over the last half millennium will continue to endure long after the arguments have ceased.