Example of widespread presence of swellings ("bottaccioli")

Blisters or "Bottaccioli"

This term refers to the swollen parts of the plaster, usually fairly small, caused by the granules of lime in the mortar that are not sufficiently slaked or spent. Over time, these granules tend to swell due to absorption of atmospheric moisture. This may cause the paint layer or plaster to become detached, due to continuing hydration, leaving a characteristic crater-shaped lacuna in the plaster. As such, the "bottaccioli" come into the category of damage to the preparatory layers caused by poor original work. Their presence is quite widespread in the Chapel in the form of blister-like swellings and lacunas.