“Guidelines for the Care of Prints and Drawings” by Margaret Holben Ellis courtesy of Martina Yamin.
The conservation problems associated with prints and drawings are often described as being either “internal” or “external”. Internal defects come from inherent factors such as poor-quality “nonartistic” wood-pulp papers or unstable or incompatible mediums. Internal conservation problems can afflict works of art on paper regardless of their age, although it is contemporary pieces whose reputation has suffered the most in this respect.
External conservation problems are those caused by such factors as improper mounting, matting and framing; overexposure to light; and dangerous temperature fluctuations. These take a far greater toil on our prints and drawings that do internal problems. By eliminating external sources of degradation, most damage can be easily prevents. The life expectancy of even contemporary works, condemned as so-called time bombs, can be extended.
Most of the worst damage occurs in mounting, matting and framing with such commonly used materials as inexpensive wood-pulp mat board, corrugated cardboard, rubber cement, animal glues, white glue, dry-mounting adhesives, masking and transparent tapes, brown gummed tape and the like. One characteristic these materials share is their chemical instability. As they breakdown with age, acidity is generated and migrates into the naturally absorbent paper of the artwork. Acids attack the chemical bonds of the long flexible cellulose molecules that make up most papers and break them into shorter and shorter segments. As a result, the paper darkens and becomes brittle in these areas. “Mat burns,” tape stains, and dark striations from corrugated cardboard are evidence that the artwork is in contact with an acidic material. In order to protect prints and drawings from such damage, they should be matted only with rag board, buffered rag board or “conservation” board, all of which have a neutral or alkaline pH (a pH of 7 of above). As the name implies, rag board is made from cotton fibers; it usually has a neutral pH. If it has been improperly sized or stored under poor conditions, however, 100 person rag board can become acidic. Buffered rag board is alkaline because calcium carbonate has been added. Conservation board, also called archival or acid-free mounting board, is made from wood pulp that has been chemically purified and buffered. Buffered boards last longer because their alkaline reserves maintain a higher pH as they neutralize acid from the surrounding environment. Thus they can help slow down the degradation of drawings done on acidic wood-pulp papers.
Wood-pulp mat board–a still, bonded sheet of bleached wood pulp compressed between two sheets of paper–should be avoided at all costs. Though it is attractive for matting inexpensive reproductions, it should never be used to mat prints and drawings. If silk mats or decorative “French” mats are used, the side that touches the artwork should be lined with acid-free mat board or paper.
Conservators generally prefer to “hinge” drawings into mats, using small strips of folded long-fibered Japanese tissue coated with vegetable-starch paste. These papers and the starch necessary to make the paste can be purchases at many art- or library-supply stores. Pressure-sensitive tapes, double-sided tapes, brown gummed paper and all synthetic adhesives should be avoided. Recently a new family of tapes, advertised as being archival, has been introduced. Although their adhesives are significantly improved, with time they become insoluble in water and require strong organic solvents for their removal.
Photo corners made of clear polyester film (Mylar) or acid-free paper are especially useful for attaching prints and drawings into mats because no adhesives come into contact with the artwork. These can be made at home or purchased.
If matting a collection of prints and drawings is not feasible, at the very least they can be stored between neutral glassine or tissue or slipped into folders made from acid-free paper. These can then be put into a sturdy solander box (specifically made for museum storage) or one constructed from acid-free corrugated cardboard. Artworks on paper should never be wrapped in cellophane, wax paper, newspaper or stored against wood or cardboard or curled inside tubes.
Frames provide additional physical protection for prints and drawings. The matted artwork is fitted into a frame with the remaining space filled with acid-free corrugated cardboard or acid-free polystyrene core board. The perimeter of the backboard is sealed with gummed-paper tape to prevent dust penetration.
When prints and drawings are framed it is important that they not come into contact with the glass or plexi used for glazing. A standard 4-ply mat board window is usually sufficient for this purpose; however, if the drawing is buckled, a thicker mat made from 8-ply or two pieces of 4-ply may be necessary. Spacers or fillets fitted around the rabbet of the frame (the “shelf” on which the glass rests) can provide a breathing space for unmatted or “floated” prints and drawings. This breathing spaces is crucial for the dissipation of trapped humidity. In areas where the drawing is in contact with the glass or plexi, moisture can easily condense and foster mold growth. Foxing, small brown spots, can result.
The choice of glass or plexi for framing should also be made with conservation considerations in mind. Drawings done with powdery media such as pastel, charcoal, chalk or heavy graphite are susceptible to the static charge created when plexi is wiped. Loose pigment particles can be literally transferred from the paper to the plexi. Drawings with flaking paint should likewise not be framed with plexi.
Light and other environmental factors such as temperature and humidity levels should be as constant as possible. Drastic fluctuations are more dangerous than gradual shifts in climate. A temperature range of 60-70 degrees Fahrenheit and a relative humidity level of 45-55 percent plus or minus five percentage points are more reasonable maintained in a home than one exact level. When relative humidity rises above 65 percent, actin should be taken since the danger of mold growth is great.
The effect of light on paper is twofold: cellulose deteriorates and colors fade or change completely. Light-sensitive media include the paints used in hand-colored prints, the inks in Japanese prints, iron-gall inks, modern colored inks made with aniline dyes, pastels, watercolors and the inks of felt-tip pens and ballpoint pens. Papers can become dark brown or fade depending upon their constituents. While all light is dangerous, certain wavelengths are more harmful to paper and colorants than others.
Ultraviolet light is invisible to humans but is especially destructive to both paper and media. UV light is found in high proportions in daylight and in slightly smaller amounts in fluorescent lighting. Incandescent (tungsten) light bulbs do not produce appreciable amounts of UV light.
Methods of removing UV light from rooms where works of art on paper are exhibited are straightforward. Blocking out all daylight, removing fluorescent tubes and substituting incandescent light is one logical way. Filtration is another method. Filtration is accompanied by the use of plastic filters, which are available in many forms. Exterior windows and skylights can be treated with UV-filtering film applied directly to the glass. Flexible blinds can be hung in windows. Panels of UV-filtering acrylic can be positioned in front of windows or suspended below skylights. Cylinders of similar filtering material can be slipped around fluorescent tubes. Finally, prints and drawings can be framed behind UV-filtering plexi except in cases where powdery media make this inadvisable. These ultraviolet-filtering rigid acrylic sheets are sold under the names UF-3, UF-4 (Rohm and Hass) and OP-2 (Cyro Industries).
As already mentioned, the intensity of light and the amount of exposure times should also be considered when displaying prints and drawings. In the United States, light intensity is usually measured in footcandles; in Europe it is measured in lux units. The proper level of illumination for works of art on paper has been much debated. It is generally agreed that 5- 8 footcandles of incandescent light with no UV present from other sources is acceptable for limited amounts of time. This figure represents an uneasy compromise between the need to exhibit an object and the desire to protect it.
The effects of exposure to light of any time or level are cumulative. For this reason prints and drawings should never be permanently displayed. Three months of exposure time per year per drawing is a prudent policy adopted by some museums. For private collectors, rotation of prints and drawings is advisable. If these lighting restrictions seem excessive, they are for good cause–light damage is irreversible, and when it is finally noticed it is too late to lower the lights.
Reference: Margaret Holben Ellis’ Book
Margaret Holben Ellis is the chairman and associate professor of the Conservation Center, Institute of Fine Arts, New York University and the Consulting Conservator of Prints and Drawings, The Metropolitan Museum of Art