Most older paintings have had organic varnish coatings applied to the canvas. Over time these varnishes yellow often to an extreme degree. The molecular structure of organic varnishes also cross links, making them more difficult to remove the longer they remain on the painting. Dirt and grime also build up on the surface making the colors less vibrant and obscuring detail. The results of removing the old coatings shown below speak for themselves.
19th Century Landscape, Private Collection, Boston, MA
The painting was cleaned of the darkened surface grime and old varnish. A new coating of non-yellowing varnish was then applied.
Mt. Washington by Benjamin Champney 19th century, Private Collection, MA.
The painting was never varnished but was covered with a heavy layer of dirt and grime. Sometimes when there is no varnish to protect the paint surface, cleaning a painting can be very difficult. This is often the case when microscopic oil droplets from fireplaces or heating systems mix with the dirt and grime forming a film that aggressively cross links.
Springtime by John J. Enneking 19th century, Collection of Fall River Public Library, Fall River, MA.
In this cleaning and restoration project, the dirt and grime were removed and the painting was lined with a new canvas support.
Mexican Landscape 20th century, Plympton Fine Arts, Plympton, MA
This painting had only heavy dirt and grime. Before cleaning, the white stucco was medium gray.
German Farmyard 19th century, Private collection, Worcester, MA.
In addition to dirt and grime this painting had a thin coating of discolored varnish. Restoration proved the sky was blue, not gray.