Nails and clamps were widely used in 19th century restoration work.

Nails/clamps
During 19th century restoration work, detached pieces of plaster that were not seriously uneven, were re-attached to the plaster by means of nails or small clamps made of copper, bronze or brass. The nails are set in specially prepared holes in the plaster, anchored with hydraulic mortar whose composition is not known, but which might be similar to the putty used for detached pieces of plaster. There is a significant number of these metal elements on the frescoed surfaces with especially high frequency (of the order of thousands) in the area where the roof vaulting meets the left wall. Consolidation carried out with this technique is still effective in about 50% of the treated areas. In most cases, the nail-heads and the holes are covered with roughly circular stucco work which is often irregular and partly covered by retouching with tempera, now discoloured.