Restoration of the Sistine Chapel frescoes smoke and exhaust fumes of the city, being "much dirtier than the ceiling proper". The building was a little unstable and had already shifted considerably prior to Michelangelo's work of 1508, causing cracking of the ceiling, the crack in the "Judith" pendentive being so large that it had to be filled with bricks and mortar before painting. The upper part of the ceiling provided Michelangelo an irregular surface due to cracks and water seepage. Continued ingress of water from the roof and from unroofed exterior walkways above the ceiling level had caused seepage which carried down salts from the building
Illusionistic ceiling painting sotto in sù". This was the prototype of illusionistic ceiling painting that was to become an important element of Italian baroque. Correggio at Parma took the illusionistic ceiling a step farther in his frescoes of Christ and the Apostles for the cupola at the San Giovanni Evangelista and in the "Assumption of the Virgin" in the dome of the Cathedral of Parma, which is Correggio's most famous work (1520–24); in these frescos Correggio treats the entire surface as the vast and frameless vault of heaven in which the figures float. In a visual continuity between the architectural interior and its