 Above the windows (the main source of ventilation), the lunettes were particularly stained from the 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.