The  NATURAL HISTORY ART GALLERY

A Collectors guide to  conservation, care and handling OF WORKS OF ART AND DOCUMENTS

 Water damage to this original lithograph by Toulouse- Lautrec caused severe cockling.  The treatment involved removal of a linen backing as well as damaging animal-based glues before flattening with controlled humidification and drying

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Questions and Answers

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what causes damage to works of art and objects on paper or paintings ?

While the causes of damage to works on paper and paintings on canvas, linen or wooden panels are often the same, the resulting problems can differ because of the different relationships of the pigment layer to the substrate and if present, the ground layer.

 Although paper is obviously fragile, many of the conditions that threaten preservation or cause its deterioration are not so obvious.  One has only to look around their home to uncover a few of the hidden enemies of family heirlooms and works of art of all mediums:  pictures stored in a hot, dry attic, or in a basement with its inherent dampness: poorly framed pictures; family photographs mounted in acidic albums with damaging adhesives; heirloom letters and documents, folded, torn and stained from exposure to moisture, relegated to a dresser drawer.  Each of us familiar with one or more of these detrimental circumstances.

Environmental Enemies

When properly made and cared for, paper, canvas or linen can last for centuries.  However, they are extremely vulnerable to damage and deterioration from environmental factors.

Humidity:  Exposure to excessive humidity can allow mold to form.  Mold cannot form unless the humidity is sustained at 70% or above.  Appropriate air conditioning or dehumidifiers can help prevent the formation of mold. “Foxing” (brownish speckling), which is caused by the chemical action of mold on colorless iron salts present in most paper, can be an obvious sign of mold.  The mold not only discolors the paper, but also feeds on sizing and paper fibers, thereby weakening the sheet. Similarly mold can penetrate the pigment layer of a painting or feed on the sizing element in the canvas from the verso.

Moisture: Furthermore, because everything expands with moisture and contracts with dehydration, as well as temperature changes

 “cockling” (severe waviness or rolling of the paper) may occur if paper is exposed to excessive humidity.  When cockling is severe or mold is suspected, the piece should be given to a competent conservator for flattening and thymolization (anti-fungus vapor treatment). Trapped moisture between the varnish and pigment layers of a painting can result in “blooming” a whitish gray film and greatly reduce the viewing quality of the artwork.

 Light: Harsh light with ultraviolet radiation can cause fading, yellowing and emmbrittlement.  Fluorescent and sun light are the most harmful.  Care should be taken in placing a piece so that the most direct morning or afternoon light is avoided.  Ask your framer about ultraviolet filtering glass and plexiglas which can be employed to limit exposure to ultraviolet light. While the opaque pigments in paintings are less susceptible to fading, many paintings incorporate transparent glazes and varnish layers that can be affected by U-V exposure.

Heat: High temperatures accelerate deterioration of paper and embrittlement of paint layers.  Works of art should not be stored or exhibited near a heat source. 

Air Pollution: Pollutants in the atmosphere can cause discoloration, embrittlement and eventual disintegration of paper fibers. More commonly, however, solid matter (dust and soot) present in the air will penetrate the paper’s surface or accumulate on the paint surface.

Insects: Silverfish, termites and woodworms can cause considerable damage.

 Varnish: Older paintings and many modern ones as well, were coated with natural resin varnishes as a protective layer. In most instances while the varnish did serve its purpose, the resin has darkened with age and exposure sometimes significantly altering and obscuring the appearance of the original.

Acid: The Enemy Inside Paper

 Flaws often are inherent in paper; consequently dangers may come from within. Early papers were produced primarily from pulp made of rag (cotton fiber).  It wasn’t until the latter half of the 19^th century that wood pulp fibers were introduced to commercially produced papers.  Lignin, a natural element which binds fibers in the living tree, becomes an unstable component in wood pulp, causing an acidic reaction. Envision the strands of paper fibers as links in a chain.  The acidic paper loses its strength, becoming brittle and unable to support itself.  Additionally, wood pulp paper fibers are short, thereby producing a weaker sheet.  Alum-rosin sizing sometimes added during the papermaking process also is a prime acid producer. All acidic paper, if untreated, eventually will deteriorate.

Use of acid-free (100% rag) paper by publishers and artists is half the solution.  Collectors also should be sure that acid-free mats and papers are used in framing their pictures.  If you have an object or collectable made of acidic paper, such as baseball cads, the deterioration usually can be arrested or significantly reduced by the conservation process of deacidification. Paintings are often framed to the edge in a wooden frame. The rabbet of the frame that is in contact with the canvas should be lined with ragboard.

Improper Framing

Contrary to the uncommon perception that an object is preserved simply because it is framed, most damage to works on paper is due to improper framing.  An adequate air space must be provided between the back of the frame and the wall on which it hangs.  In addition, an air space is required between the object and the glass or any glazing material.  Without provision for correct ventilation, framed works hung on exterior wall can suffer damage due to condensation.

 Non- archival matting materials and adhesives commonly used in framing have acid content.  The acid migrated into the art or document causing the characteristic yellowing and embrittlement often associated with aged paper.  Ironically, most paper objects made prior to 1860 are inherently acid free and have been damaged through prolonged contact with acidic materials utilized in the framing process. Archival framing is an essential aspect of conservation.

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