Micro mosaics like these were done in the 18th and 19th centuries by the same workshops in Rome that meticulously copied all the paintings in the central nave of St. Peter’s, and replaced them so that the originals could be kept in a humidity controlled, incense-free environment. It was even noted, at the time, that the atmosphere inside the huge volume created by the enormous dome, had its own weather – and sometimes even created clouds that would hover in ...