TYPICAL APPLICATION OF PETROGRAPHICAL STUDY OF PAINTED PLASTERS AND ASSOCIATED PIGMENTS FOR THE SUPPORT OF A CONSERVATION PROJECT

• E. Polychroniadou (Conservator- curator, 13 Omirou str., N. Psychico, 154 51 Athens, Greece)
• E. Chiotis, E. Demou, D. Tarenidis (Institute of Geology and Mineral Exploration, 70 Messoghion str., 115 27 Athens, Greece)

The samples studied hereby come from the wall paintings of the Meliades residence in Chios built in 1880 and the Diamandara residence in Inouses, built in 1920, following the type of mansions of Smyrni, Asia Minor. The alterations mainly observed on the ceiling and wall paintings of the Meliades residence were flaking and disintegrating of the pigment layer, and loss of cohesion of the rendering to the support. Same type of deterioration is observed on the Diamandara residence. Additionally, stains of organic material are clearly observed on the pigment surface. The conservation project aims at the identification of the causes of alterations and the selection of the appropriate treatments.

Thin sections of the plasters were studied in polarized light, in combination with XRD and SEM, the latter ones applied especially for the identification of pigments. The features studied in the plasters were:

The adhesion of the pigment to the plaster is better in the case of lime plasters as compared to gypsum plasters. In the first case the pigment penetrates well into the lime plaster and is thicker, whereas it is thinner and superficial on the lime plaster.

The pigment is a mixture of iron oxides, zinc oxide and cerussite, supplemented by some organic materials, which have not been identified yet. The paintings were finally covered by some kind of glue or varnishing organic material well connected with the pigments, which has cracked and caused the detachment of the pigment from the underling plaster.