Most of the following procedures should be performed by a professional conservator who specializes in the treatment of paper. This leaflet describes some of the principal operations carried out by paper conservators. The treatment chosen for any artifact or collection should be the outcome of communication between a conservator and the client or custodian after the conservator has examined the artifact. There are many variations and different levels of treatment, and the conservator may offer alternatives. The procedures ultimately chosen depend on several considerations. These include the condition of the artifact, its future use, its aesthetic importance, what the media will allow, and, inevitably, the client's financial resources. The client should feel free to discuss the treatment with the conservator and ask questions.
Treatment is always preceded by a careful examination of each object. Before beginning work, the conservator provides a written report outlining the proposed treatment and estimating its cost. Magnifiers and ultraviolet lamps are among the tools that may be used during the examination. The solubility of all media is tested prior to any water or solvent treatment.
During the course of treatment the conservator keeps written notes on all procedures, carefully noting any chemicals that are used. Photographs are taken of each object before and after treatment, and occasionally during. Photographs of selected individual items that represent the condition of a large group of similar objects may be sufficient when photographing every one would be impractical. Following treatment, a written report is given to the client with copies of the photographic record.
Superficial grime, dirt, and soot are removed with a soft brush, nonchemical vulcanized rubber sponges, or nonabrasive erasing materials such as vinyl erasers, both in blocks and ground up into granules. Cotton dampened with organic solvent is also sometimes used to remove surface dirt.
Accretions, including insect specks and mold residues, are normally removed by scalpels, aspirators, or specialized vacuum cleaners. Mold and insect deposits are best removed individually by mechanical means. A small vacuum aspirator or a HEPA vacuum cleaner is recommended for lifting mold. It is not possible to eliminate all traces of mold, since the mycelia may be deeply rooted in the paper. Fumigation, once a standard treatment for mold and insects, is now seldom done because chemical fumigants can have adverse effects both on personnel and on artifacts. Deep freezing may be appropriate to kill insects.
When absolutely necessary, flaking or friable media are consolidated with an appropriate natural or synthetic material to stop or at least retard ongoing loss. When it is desirable to wash a paper artifact, small areas of water-soluble color can sometimes be fixed with brush applications of a dilute synthetic resin. This treatment can make it possible to wash without any loss of color, but it is practical only for isolated areas of soluble media. Occasionally the photograph-based portrait drawings known as “crayon enlargements” are spray-fixed because otherwise they cannot withstand needed conservation treatment. Fixatives and consolidants should be stable, non-yellowing, and reversible. Fixatives are never used on pastels, however, because a permanent color change can result.
If an object has been backed with a support that is not part of its original structure and the backing is destructive or inadequate, it should be removed if possible without putting the object at risk. Sometimes backing removal can be done in a water bath. If the object cannot be put in water, dry removal by mechanical means is necessary. Steam or local application of moisture can assist with mechanical backing removal, especially of the final layer of a backing immediately behind an object. Removing fragile paper from a solid backing is time-consuming and therefore costly. It is often difficult for a conservator to know in advance how long a backing removal will take or how much it will cost.
In the past, repairs were often made using materials harmful to paper, such as commercial tapes and adhesives that stain. Repairs made with water-based adhesives such as animal glue can be removed in a water bath, by local application of moisture, or with poultices or steam. Synthetic adhesives and pressure-sensitive (self-adhering) tapes usually have to be dissolved or softened with an organic solvent before they can be removed. Heat is sometimes helpful to remove these repairs.
Water washing is often beneficial to paper. Washing not only removes dirt and aids in stain reduction, but it can also wash out acidic compounds and other degradation products that have built up in the paper. Washing can also relax brittle or distorted paper and aid in flattening. For these reasons artifacts that are not visibly discolored or dirty might still benefit from washing. All media are carefully tested beforehand for water sensitivity. When materials permit, objects are immersed in filtered water. On occasion, a carefully controlled amount of a chemical compound material is added to the water to raise the pH to a slightly alkaline level. This assists in the cleaning process and in the neutralization and removal of acids. Artifacts with soluble media may be locally washed, float-washed, or washed on a suction table.
Although simple water washing reduces acidity, the addition of an alkaline buffer to paper is sometimes recommended. This is appropriate for papers that will be subject to acid hydrolysis even after washing, acidic papers that cannot be washed, and acidic papers that will be encapsulated. Sometimes alkalization is achieved by immersion in an aqueous solution of an alkaline substance such as magnesium bicarbonate or calcium hydroxide. If water-soluble media are present, the artifact may be treated nonaqueously with an alkaline salt dissolved or suspended in organic solvent. Nonaqueous solutions are usually applied by spraying. While the addition of an alkaline buffer is often beneficial, such chemicals may cause alteration or even damage to certain components of a work of art. Some colors, for example, may change if subjected to alkaline conditions. This change may be immediate or may occur over time. For this reason alkalization is not recommended for all materials. Like all conservation procedures, the decision to alkalize must be made on a case-by-case basis and should be left to a qualified conservator.
Tears are carefully aligned and then repaired, usually on the reverse, with narrow strips of torn Japanese tissue. The strips are adhered with a permanent, nonstaining adhesive such as starch paste or methyl cellulose. Sometimes synthetic adhesives are used when an artifact cannot tolerate moisture. Fine, translucent tissue is used to avoid thickening and to avoid obscuring writing on the reverse, if present.
Holes or paper losses may be filled individually with Japanese paper, with paper pulp, or with a paper carefully chosen to match the original in weight, texture, and color. The latter is the most time-consuming (and consequently the most expensive) option, usually reserved for works of art. If the conservator has the necessary equipment, multiple pulp fills on a single sheet can be achieved in a single operation by leaf-casting the sheet on a specialized machine. For archival objects of less aesthetic importance, conservators may simply back them (see below) and allow the backing sheet to fill the lost areas visually. Backing sheets can be toned to make the discrepancy in appearance of the areas of loss less jarring.
Especially weak or brittle papers or sheets with numerous tears may be reinforced by backing them with another sheet of paper. As a rule, the backing should be somewhat lighter in weight than the original. Japanese paper, either handmade or machine-made of high-quality cellulose fibers such as kozo, is the usual lining material, although western paper is occasionally used, especially for photographs. The backing is adhered with a dilute starch-based paste, methyl cellulose, or a mixture of the two.
Historically, paper artifacts, especially oversized objects such as maps and posters, were backed with woven fabrics like linen or muslin. Woven materials respond differently to climate changes and therefore are not entirely compatible with paper. Occasionally fabric is used with very large objects that will not otherwise remain flat, or require extra support for their weight. Historic wallpaper is usually lined with cloth so that it can be removed from the wall in the future. In such cases the object is lined first with paper, which isolates the object from the fabric, and then with high-quality washed linen or cotton.
Inpainting is done by judicious application of watercolor, acrylic, gouache, or pastel to filled areas of loss or to minor surface losses such as scratches, abrasions, and media losses along tears. The goal is to make these damages less distracting. Care should be taken to confine the retouching to the area of loss. Normally areas of design are not replaced, although simple design areas such as borders may be completed. Conservators do not attempt to make their retouching absolutely invisible. They are obliged to make it possible to distinguish their work from the original when a researcher or other viewer examines the work closely. Incidentally, retouching or “strengthening” of faded writing is always inappropriate for a professional conservator.
Bleaching is time-consuming and tricky. It is warranted only when staining or discoloration compromises the aesthetic value of a work of art or exhibition material. When possible, bleaching should be undertaken by exposure to artificial light or to sunlight, or it can be done with chemicals. Conservators often prefer bleaching with light because it is gentle and not harmful to cellulose. Some stains, however, require the use of chemicals. Sometimes a combination of bleaching methods is needed to achieve a desired result. Bleaching does not enhance the preservation of a work of art, only its appearance.
Chemical bleaching of paper must be done under carefully controlled conditions with a bleach that is known to be safe for both the paper and the medium. The bleach must be removed from the paper after treatment. Chemical bleaching is always followed by a thorough water rinsing of the treated area. Whenever possible, the chemical is confined to the area of stain, but sheets with extensive staining or discoloration are occasionally bleached overall. Such objects might be immersed in a bath, but more often the solution may be brushed or sprayed on. Only a handful of chemical agents are considered sufficiently benign to be incorporated into conservation treatments. Some chemicals commonly used in the past have proven to be harmful in the long run and have even caused the return of staining more severe than ever. Staining can return even using the safest and most up-to-date methods. Some stains, such as the brown spots referred to as “foxing,” seem more liable to reappear if they are exposed to excessive relative humidity after treatment.
Flattening is always necessary following aqueous treatment. It is usually done between blotters or felts under moderate pressure. Objects that have been lined are sometimes dried and flattened by stretching on a Japanese kari-bari screen or on a flat surface such as an acrylic panel. Experts do not necessarily expect paper objects to lie perfectly flat. Paper naturally undulates as it responds to environmental fluctuations.
Once an object has been treated, it must be properly stored in an archival folder or other enclosure. Special housings such as matting, framing, and polyester film encapsulation give extra protection to objects. In some instances these enclosures eliminate the need for more invasive reinforcement procedures such as lining.
This method of protection and reinforcement is the most appropriate for archival research materials, as it provides excellent protection during handling. Encapsulation is done by sandwiching the object between two sheets of polyester film (Melinex), usually 4 or 5 mil thick, and sealing the film at all edges. Conservation laboratories have special equipment for sealing the film ultrasonically or with heat. Because polyester carries a static charge, encapsulation is not recommended for materials with loose, flaking media, nor should it be used for acidic papers. It has been demonstrated that the deterioration of acidic materials is accelerated by encapsulation, and leaving corners of the encapsulation open has little if any effect on this problem. In some situations the need to protect materials during handling may outweigh this concern. Conservators often recommend including buffered or MicroChamber paper in an encapsulation behind an acidic artifact.
While many museums routinely use mats for storage of prints and drawings, this type of housing is especially suited to works of art or artifacts intended for framing. Mats are usually composed of a window and backboard of 4-ply 100 percent ragboard or lignin-free archival board. The object is attached to the backboard with hinges of Japanese paper and starch paste or with corner supports or edge strips. The window mat provides separation of the object from the glazing in a frame and from the next mat in a stack. If there is an inscription on the back of an object, a second, smaller window can be cut into the backboard to reveal it. Matting protects study collections when researchers handle them because they handle the mat, not the art.
Once matted, an object can be safely sent to a framer for a new frame or it can be returned to an existing frame. If an existing frame is reused, it may need alteration to make it acceptable from a conservation point of view. For example, if the frame fits so tightly that the edges of the object come in contact with the wood, the frame opening should be enlarged or lined with a barrier material. Some frames with shallow openings must be deepened to accommodate the total thickness of a mat, the glazing, and the backing layers needed to protect the artifact. Frames can be made deeper by building up their back with strips of wood screwed in place. Ultraviolet-filtering acrylic or glass is recommended as a glazing. Acrylics such as UF-3 Plexiglas carry a static charge, so they are not appropriate for pastels or other objects with flaking or powdery media.
For further information about these enclosures, see the NEDCC preservation leaflet "Matting and Framing Art and Artifacts on Paper."