The Care and Preservation of Pastels

by Marjorie Shelley

Sherman Fairchild Conservator in Charge of Photographs and Works on Paper, The Metropolitan Museum of Art .

Reprinted from the PSA 33rd Annual Catalogue

Brilliant color that does not yellow with time, a velvety, matte surface unlike any other medium, dry color that is capable of a range of effects. These characteristics are distinctive to pastel. They result from the medium’s composition: a blend of finely ground pigment and white extender coalesced with a minimal amount of binder – the latter merely enough to enable the artist to grasp the stick of color between the fingers yet crumble when stroked across a support. It is this powdery property that accounts for the delicate surface of works in pastel, and underlies the issues that must be considered in their care and preservation.

Fixing:

The greatest glory and the greatest weakness of pastel is its powdery composition. These opposing factors have provoked countless debates among artists as to how to stabilize these works, and which substances to use. While some materials and methods may suit a particular artist’s goals, there is no ideal fixative. In theory, any liquid applied to pastel will penetrate the spaces between the fine particles of powder and cause certain colors or the overall composition to become dull or darken, thereby diminishing its characteristic light-scattering property. Fixatives can also alter the color of exposed paper. These factors should be kept in mind if you choose to fix your pastel, and if so, it is best to experiment in advance with the materials you plan to use.

Framing:

If you do not fix your pastel, its surface can still be well protected. This is most effectively done by framing, as this will avoid accidental smudging and abrasions, and the settling of dust. Whether the support is paper, canvas or wood, at least ¼ inch space should be provided between the surface of the composition and the inner side of the glazing. This will protect against rubbing and the possibility of condensation and subsequent staining should there be a rapid drop in temperature. This space can be created by using a deep mat bevel, or inserting spaces or lifts between the art work and the glazing. Pastels on loose sheets of paper should be hinged at all edges or over matted to avoid cockling and the consequent rubbing of powder against the glazing once framed. Matting materials should be 100% ragboard. This will help to avoid discoloration due to acidity, and will provide mild buffering action against changes in humidity. For glazing, use only antistatic materials to avoid having the powder lifted off the surface of the composition. Such products include ordinary glass, and nonreflective glass incorporating an ultraviolet barrier (such as Schott Amiran, Denglass Water White, or Tru-Vu Museum Glass). Acrylic sheeting should be used with caution because of its static charge. If it is used, apply anti static solution to the inner and outer sides of the sheet. Guard against large thin sheets of acrylic because they will bow and rest on the surface of the pastel, and avoid turning any pastel face-down.

Unframed Works:

Pastels that are not framed are best protected by storing individually in flat file drawers, or shallow archival boxes. When unframed pastels must be stacked, their surfaces can be protected with interleaving paper. Choose a smooth, hard surfaced, non fibrous paper, such as glassine or silicone release paper – avoid materials that have a static charge such as Mylar and various films, and do not put pressure on the top of a pile of pastels. Most important is to avoid any friction in positioning or removing the paper from the surface of the pastel. It is best to hinge or position the pastel on a sheet of ragboard larger than the dimensions of the art work, and to tape the protective paper, which is larger than the pastel, to the ragboard. This will help to keep the pastel in place, and provide a resilient surface for lifting it. The margins of this support will also provide an area to grasp, rather than placing hands or fingers on the work of art itself.

Environmental Factors:

Light: While laminated glass with a UV barrier is one of the greatest advancements in offering pastel protection from damage due to light, caution still must be used in displaying pastels. Some dyes and pigments used in the fabrication of the medium, as well as exposed areas of paper, are vulnerable to fading when subject to high levels of illumination for prolonged periods of time, such as the years or decades that a pastel hangs in one’s home. To slow the process of color alteration and fading, blinds or curtains should be closed, particularly when the work is not being viewed. When the work of art will not be viewed for an extended period of time, such as during a vacation away from home, felt or other dark opaque cloth may be hung over the framed composition. If possible, display pastels in hallways without windows. Avoid direct sunlight and fluorescent lighting: both are rich in ultraviolet light and will provoke fading.

Humidity and Biodeterioration:

Being composed of many potentially reactive organic constituents, works in pastel must be protected from adverse environmental conditions. High levels of humidity pose a particular concern. The binders used in the fabrication of pastel, the papers used for its execution, and mounting adhesives make these works susceptible to mold and mildew if exposed to humid conditions for more than 24 hours. If conditions are not rectified, the mold that forms will remain active, and can cause color changes and foxing – the dark spots resulting from enzymatic activity of microorganisms. Humid conditions will also provide undulations in paper that can rub against the glazing and off set the pastel. Moisture absorption can be significantly reduced with a moisture barrier that can be made by covering the back of the matted composition, or the back of the frame, with a sheet of Mylar that is taped in place. To reduce the attraction of insects, use acid-free framing and matting materials, and a dust seal to cover the gap between the frame and the backboard. Strips of tape or a sheet of Kraft paper covering the entire back of the composition and adhered with double-sided tape may be used for this purpose. Avoid storage in dark, musty areas in order to minimize the possibility of mold growth and insect activity. Should mold be detected, it is best to unframed the pastel, expose it to dry, clean air, and reframe with acid-free materials. With cleanliness, good quality materials and maintaining environmental conditions at approximately 68-72F and 50% relative humidity, these problems can be prevented.

Travel:

Historically one of the reasons claimed for fixing pastels was to make them safe for travel, as glass was apt to break in carriages subject to the potholes and bumps of cobblestoned roads. While it is still essential to avoid vibrations that can dislodge pastel powder, other precautions can be taken. If glass is used for framed pastels, taping it will protect against splintering and damage to the pastel should breakage occur. Additionally, foam padding placed in direct contact with the glazing and frame backing, and tightly packing the artwork will prevent movement in transit. Pastels framed with acrylic sheeting do not need to be taped. Pastels should travel flat – face up in a horizontal position – whenever possible, and should not be turned upside down. If neither framing nor a horizontal position is possible, stability can be provided by packing the pastel between two sheets of ragboard or acid-free cardboard: the pastel should be hinged to the backboard and then covered with silicone release paper or glassine as described above. Tape the edges of the package together in order to protect from movement in transport. It is not advisable to roll pastels, but if this is unavoidable, place protective paper on the surface of the art work and wrap it around a cardboard tube with a diameter of at least 6 inches; the diameter will depend upon the size of the pastel. Cover the rolled pastel with protective paper and tape to secure. For transport or posting, place the rolled pastel into a larger mailing tube.

Preserving a work in pastel requires being mindful of environmental conditions, appropriate matting and framing materials, and avoiding vibrations. Despite the fragility of its surface, a pastel can last as long as work in any other medium, and will preserve its color and distinctive matte surface with the same freshness as when first applied.

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