Restoration of the Sistine Chapel frescoes of the work. Based on this decision, according to Arguimbau's critical reading of the restoration data that has been provided, the chemists of the restoration team decided upon a solvent that would effectively strip the ceiling down to its paint-impregnated plaster. After treatment, only that which was painted "buon fresco" would remain. According to critics, the inherent problem with this approach is that it relied heavily upon an assumption that Michelangelo only painted "buon fresco", that he was always satisfied with the result at the end of the day, and that in four and a half years spent on the
Sistine Chapel congregations. These included the Christmas Day and Easter masses, at which the Pope himself was the celebrant. The other 27 masses could be held in a smaller, less public space, for which the "Cappella Maggiore" was used before it was rebuilt on the same site as the Sistine Chapel. The "Cappella Maggiore" derived its name, the Greater Chapel, from the fact that there was another chapel also in use by the Pope and his retinue for daily worship. At the time of Pope Sixtus IV, this was the Chapel of Pope Nicholas V, which had been decorated by Fra Angelico.