Considerations in Our Cleaning Decisions

Considerations in Our Cleaning Decisions

Part 6 of Conserving a Canaletto

It's likely you have a photograph, painting, illustrated card, or drawing that just doesn't look the same as it did when you first brought it home. Heck, you probably have a shirt that isn't as bright as it once was and maybe there's a stain or two on it reminding you of a not-so-graceful moment. The world is a tough place and the effects of temperature, light, water/humidity, and other humans mark us and our things without fail.

Artists' materials change over time just like our everyday objects and even ourselves. Paint contracts as it dries, often creating a fine craquelure, or cracking, pattern. Oil paint in particular, can darken over time if not exposed to ultraviolet light and will become more transparent over time; in some cases exposing artist’s changes to the composition, known as pentimenti. Some pigments fade more than others and change, altering the artist’s original vision. Natural resin varnishes, commonly applied to traditional paintings once they were considered finished, visibly darken and turn into an amber color within seven years of normal museum light exposure. The aging and discoloration of these coatings darken the picture overall, limiting the viewer’s ability to see artist-painted details and tonal contrasts. All of these issues make it tough for the viewer to appreciate or even see the masterful illusion Canaletto created of a three-dimensional scene on a two-dimensional surface. Further complicating matters, old losses where paint has flaked off, and then painted over by earlier artists or restorers, have also changed—making them more visible, and ultimately disfiguring the overall artwork.

So what are we to do? As described by the late Gerry Hedley, a conservator at the Courtauld Institute in London, these changes are all "...signifiers of age." As viewers of older pictures we expect to see some of these signifiers like a fine craquelure pattern in the paint or even pentimenti. There is little one can do about some changes like the fading of paints whereas it is not uncommon to at least partially remove discolored varnish layers. Often cleaning involves emphasizing certain age signifiers over others.

From a conservation perspective, there are three ways, loosely described, to approach the cleaning of a painting:

  1. complete varnish/restoration removal
  2. thinning of the varnish layer and either adjustment/removal of old restorations
  3. partial cleaning and either adjustment/removal of old restorations

Each technique emphasizes different aspects of a painting’s history and all are equally valid cleaning techniques.

Complete varnish/restoration removal

This approach emphasizes revealing what remains of the artist’s hand. By removing all discolored varnish and restorations, the conservator and curator are faced with the original surface. Its exposure reveals the artist’s use of color, line, and shade. Signifiers of age left behind are craquelure and previous damages to the paint and support. Risks include inadvertently removing original material. Although potentially out of so-called tonal harmony due to age and history, the conservator has a ‘clean slate’ in order to recreate as thoughtfully as possible what are believed to be the artist’s original tonal harmonies.

Varnish thinning

This approach, by definition, considers the presences of an old varnish an important age signifier. The warm, mellow surface created by the discolored varnish is generally considered visually pleasing. Though a difficult technique to execute, there is little concern about removing potential original material.

Partial/selective cleaning

This approach emphasizes the reconstruction of the painting’s tonal harmonies. Some colors may darken while other may get lighter over time creating tonal extremes. The selective cleaning technique tries to lighten the darks and tone the lights so the picture is not visually jarring. With this technique, the conservator makes aesthetic judgments during the cleaning process—in contrast to the complete varnish restoration removal technique where aesthetic adjustments are made in the ‘restoration’ phase of treatment.

Given the picture’s condition and treatment history, Timothy and I both agreed that the old restorations should be removed as safely as possible and the uppermost varnish layers removed. I will try to leave behind residues of the oldest varnish layer in the troughs of the damaged brush strokes, thereby, when viewing the picture, slightly accentuating them. The goal is that the overall tonality of the picture will be much cooler and brighter, but not stark, after cleaning.

This post is one in a multi-part series by Denver Art Museum staff on a long lost painting located in our collections. Find links to more from the series.

Image credit: Giovanni Antonio Canal, called il Canaletto. Venice: The Molo from the Bacino di S. Marco, about 1724. Oil on canvas. Bequest of Charles Edwin M. Stanton, 2009.336.

James Squires was the paintings conservator at the Denver Art Museum.