 In other words, Michelangelo did not work "a secco"; he did not come back later and add details onto the dry plaster.The restorers, by assuming that the artist took a universal approach to the painting, took a universal approach to the restoration.A decision was made that all of the shadowy layer of animal glue and "lamp black", all of the wax, and all of the overpainted areas were contamination of one sort or another