Sistine Chapel ceiling ceiling include the four so-called Major prophets: Isaiah, Jeremiah, Ezekiel and Daniel. Of the remaining possibilities among the Twelve Minor Prophets, the three represented are Joel, Zechariah and Jonah. Although the prophets Joel and Zechariah are considered "minor" because of the comparatively small number of pages that their prophecy occupies in the Bible, each one produced prophesies of profound significance. They are often quoted, Joel for his "Your sons and your daughters shall prophesy, your elderly shall dream dreams and your youth shall see visions". These words are significant for Michelangelo's decorative scheme, where women take their place among men
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