For five hundred years, water infiltrations and smoke from candles used to light the cathedral had seriously damaged the work. Indeed to the point that several pieces of frescoes by Zuccari came unglued, while other portions by Vasari crumbled. When scholars found themselves before the work, given the gravity of the situation, they decided to undertake a meticulous and lengthy restoration.
Restorers worked with extreme care and precision reattaching and reconstructing the ruined parts, employing the most modern restoration techniques known to date. The restoration of the cupola and frescoes, begun in 1989, took fifteen years to complete and the work of two hundred technicians who worked on a suspended site, 90 m from the ground and on twenty-four levels.
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To perform restoration, the Opificio delle Pietre Dure conducted all the necessary analyses, using advanced technologies for micro biological analysis and ultraviolet and infrared photographic detection. Today, thanks to these modern technologies, monitoring is effected by a system, unique in the world, composed of 160 instruments designed by the National Military Geographic Institute.
The system is operative 24 hours a day and can be programmed to record data every six hours. This supplies the means to evaluate possible give caused by all and any variations provoked by heat and humidity, vibrations of city traffic or possible telluric activity which could place Brunelleschi's cupola in danger.
