Matteini, Mauro:

Innovative approaches for the conservation and restoration of mural paintings

The modern conservation practice of mural paintings dates from the sixties. In that period new methodologies were introduced based on innovative materials and chemical processes that deeply influenced the practice of conservation during the next decades, up to now.

Before the sixties treatments used in restoration have been based on traditional materials and methods.
Cleaning of paintings has been frequently carried out by using strongly alkaline, non volatile, agents. Their infiltration and permanence inside the paint layers and the plaster frequently caused both immediate and long term damages.

Consolidation was based on the same natural products that the old artists had been using as binding media, such as egg, casein, vegetable gums, sometimes oils.
During the sixties, besides introducing new treatments and materials two main methodological approaches were differentiated. A first one, the organic-polymeric line, was based on the use of synthetic polymers, initially vinyl resins and later – with much higher success and diffusion –acrylics, among which the famous Paraloid B72. The other line, the mineral-inorganic one, started at the end of the sixties with the revolutionary process of barium hydroxide and, parallelly, with the esters of the silicic acid.
Since that period significant steps forward were made. Most of progress was possible thanks to the acquisition obtained through diagnostic studies which deeply clarified the mechanisms of decay and allowed to address treatments towards more appropriate solutions.

Nevertheless, the restoration of this typology of works of art remains difficult and critical. Many problems, mainly those related to some categories of soluble salts, seem to be not solvable through restoration. Preventive conservation and planned maintenance, in those cases, appear to be more appropriate even though not totally satisfactory approaches.

Coming back to the restoration treatments, personally, I always privileged the mineral- inorganic line, especially for reasons of durability and compatibility.
In that frame, in the presentation the method of the ammonium oxalate and some more recent approaches based on phosphates will be illustrated.