Purity of soul isn't essential, but admirers of Leonardo Da Vinci's deteriorating masterpiece "The Last Supper" now must submit to another purification - this one physical.
The installation of climate-control and air-filtering equipment forced a seven-month closure of one of the favorite tourist destinations in this northern Italian city. It reopens Saturday.Now, though, visitors must pass through two separate glass cabins. They will pause for about 15 seconds in one, where filters imperceptibly will take impurities outside and pump in clean air.
"The new system eliminates 99.97 percent of the dust, sulfuric acid and sulfur dioxide. Polluting substances, taken in by the flow of visitors, were threatening the preservation of the fresco," Lucia Gremmo, superintendent of the city architectural properties, said Friday.
The purification system cost about $1.4 million.
Leonardo painted the renowned work on the wall of a friars' refectory in 1497.
Pollution is only the latest threat to it. Napoleonic troops used the refectory as a stable, and Allied bombs fell on it during World War II.
Leonardo's use of tempera - a technique less durable than true fresco painting, which is done on wet plaster - also caused the work to deteriorate severely.
The painting has undergone 19 known restorations in four centuries.
A huge one, started in 1978, has restored colors and details to about half the wall and is expected to continue for several more years.
Officials said each group of visitors will be allowed to stay 15 minutes.