Sistine Chapel ceiling how the work progressed. It was customary for fresco painters to use a full-sized detailed drawing, a "cartoon", to transfer a design onto a plaster surface—many frescoes show little holes made with a stiletto, outlining the figures. Here Michelangelo broke with convention; once confident the "intonaco" had been well applied, he drew directly onto the ceiling. His energetic sweeping outlines can be seen scraped into some of the surfaces, while on others a grid is evident, indicating that he enlarged directly onto the ceiling from a small drawing. Michelangelo painted onto the damp plaster using a wash technique to apply
Restoration of the Sistine Chapel frescoes have been predicted by previous restorers. One of the major dangers to the frescoes is automotive exhaust, and they are also vulnerable to the effects of the crowds of tourists that pass through the chapel every day, bringing with them heat, humidity, dust and bacteria (the latter of which can biodegrade paints and pigments). The clean plaster surfaces are more in danger from these destructive elements than they were when they were covered with a layer of smoky wax. Previously, the Sistine Chapel's only ventilation was from its windows in the upper level of the walls. To prevent exhaust fumes