The Paintings conservator is responsible for the care of 381 paintings in the Winterthur collection as well as their frames and the painted surfaces on other objects such as furniture and clock dials. Paintings conservators address the structural problems of paintings such as torn or deteriorated canvas or stretchers that cause distortion and paint loss as well as the paint layers and varnishes applied to them. Paint on any substrate (canvas, wood, or metal) may begin to flake due to physical damage, corrosion, or dimensional changes in the substrate caused by unstable relative humidity. Wood and fabrics like canvas absorb and release moisture as the relative humidity varies resulting in dimensional changes. Since the paint layer does not absorb moisture at the same rate, it cannot change with the substrate and the resulting stress can cause it to flake off. Varnishes and coatings applied to the surface age and darken with time and may require cleaning or removal and replacement.
Frames are an integral part of paintings visually and structurally since they provide protection and the means to hang a painting. Traditional frames are composed of wood, compo (a plaster-like mixture of chalk, glue, resin, and oil ) and various gilt and painted finishes that are subject to abrasion and physical damage that causes breakage and loss of decorative elements.
Like other parts of Winterthur's collection, paintings are maintained at a stable temperature and relative humidity of 50% and protected from excessive light that can accelerate aging of the varnish and fading of some pigments. Proper framing requires a backing board to protect the canvas and secure hardware to insure safe hanging.
Painting on Glass
Glass is among the most challenging substrates artists used for paintings because of its fragility and the smooth surface that makes paint adhesion difficult. This reverse painted glass panel (1979.0225) was made in China for the American market sometime between 1804 and 1810. The image is based on a print by Samuel Harris, published in Boston, MA in 1804.
The artist applied oil paint to one side of a glass panel, but the image is viewed through the glass, so we see the first brush strokes the artist made. The central image of Liberty was painted very thinly with little or no layering. The image appears nearly identical whether viewed from the front or the back. In the background and legend, the gold stars and lettering were applied first and additional layers painted around and "behind" the gold.
The paint layer is in generally good condition, but open joins in the wood backing board allowed dirt and dust to accumulate on the back of the panel. Soft brushes and cosmetic sponges were used to gently remove the loose dirt and debris.
The loose dirt could not be removed from the dark blue background behind the inscription, where the paint was actively flaking. Fortunately, the gilded lettering remained well attached to the glass. Because the paint layer was so thin and the flakes were very small, it was impossible to use a brush to apply adhesive. A fine mist of a reversible, non-yellowing, water soluble adhesive was applied using a nebulizer. This tool delivered the adhesive in tiny droplets with a gentle air flow. After multiple applications, the flakes were gently laid down on the glass.
The glass panel has a noticeable bow, suggesting that it was cut from "cylinder" glass. A smooth ridge of glass at the lower proper right corner appears to be a remnant of the outer rim of the full sheet of blown glass.
The original glue blocks used to hold the glass in its frame were all missing, replaced by long strips of wood that were putting undo stress on the warped glass. After cleaning and consolidation, the glass panel was refit in the frame with new glue blocks that were attached to the frame with a reversible adhesive. The bowed panel is supported by a foam insert in the frame that conforms to the shape of the glass.
When the original wood backing board was re-installed, an additional layer of paper was attached to the back of the frame to prevent dust from accumulating again on the painted surface.
Object credit: 1979.225 Gift of Mr. and Mrs. Robert L. Raley
Bottom Image: (Left) Close-up of dirt removal. (Right) Reverse of painting after cleaning and consolidation.