Under a contract with National Park Service for stabilization of the paintings, Cunningham-Adams’ pretreatment examination and analysis identified a number of interrelated mechanisms of deterioration. Cold-induced brittle fracture of the paint layer had resulted in a rectangular network of fissure in and through the paint layer, on about a 1.5 mm grid throughout the paintings’ surfaces. Water condensing on the painting surface had penetrated the paint layer through these fissures, and had caused cyclic out-of-plane plastic expansion of the water-sensitive ground followed by isotropic contraction. These cycles propagated the paint layer fissures into the ground, and cupping of the paint-and-ground fragments, which caused adhesion loss from the fabric support, in places. In addition, the water transported cations from the ground pigment to the surface, where they formed salts that eroded the paint layer surface and further propagated the fissuring. Freezing water aggravated all of these problems. Thermal motion of the support slabs caused local strain concentrations in the paintings at the joint slabs; biological commenced in the resulting voids.
Our 1995-96 treatment included removal of ambient dirt, bird droppings, varnish residues, and salt deposits; impregnation of the paint and ground layers and support slab joints with a micro-crystalline wax and ethyl methacrylate copolymer B72 mixture; and application of a protective coating. This treatment consolidated the fragile paint and ground layers, and greatly reduced the rate of moisture transport within the painting structure, which was the fundamental cause of continuing deterioration. As an incidental result, the treatment also re-saturated the original pigments by restoring the refractive index of the paint layer surface.
Technical analysis included EDX and XRD analysis of salt deposits, SEM analysis of micro-biological deposits, and FTIR analysis of medium and ground. Cunningham-Adams’ analysis of data from its climate sensors and regular IR surface temperature measurements clarified the microclimates of the paintings, and suggested simple intervention techniques.