Hundreds of tourists (mostly Japanese) last month lined up outside the Dominican convent adjoining Santa Maria delle Grazie in Milan to visit Leonardo’s Last Supper. The painting was back on view after having been closed for two months to allow restorers to work on the faces of Christ and the apostles. Painted for the convent’s refectory from 1494 to 1497, the work had already deteriorated badly by the beginning of the sixteenth century. This was due largely to Leonardo’s use of tempera, a technique less durable than true frescoe painting which is applied to wet plaster. In the last few centuries the work has undergone nineteen known restorations. It was twice repainted in oils in the eighteenth century. In 1943 the vault and right wall of the refectory were destroyed by bombing. The latest project was begun in 1978 by the local Soprintendenza and the Istituto Centrale del Restauro in Rome. Restorers have attempted to undo the damage of previous restorations and, in the process, details such as the colour of the Apostles’ robes reflected in the pewter plates and the glass carafes on the table have been revealed. To prevent further deterioration by pollution, entry to the refectory is through two separate glass cabins which were installed in 1995. Between the cabins, filters remove impurities brought in from the outside, such as dust, and pump in clean air. Viewing is now limited to groups of twenty people for fifteen minutes. By next year a reservation system should be in place to shorten waiting times. The project is set to be completed in the next twelve months.