Although it is neither necessary nor desirable to remove all dirt or discoloration from old papers, surface cleaning sometimes improves the appearance of an artifact. Surface cleaning can also remove substances that might eventually damage paper, or that could be transferred to other papers during handling.
Manuscripts, maps, book pages, and other documents may benefit from surface cleaning. Brittle newspapers, photographs, or fine art prints might be harmed by inexpert attempts to surface-clean them. Works of art in any media that are not firmly bound to paper, such as pastel, pencil, or charcoal, might be lifted or smeared by cleaning, and they usually cannot withstand surface cleaning at all. Examination of paints and thicker inks under magnification may reveal minute flaking not obvious to the naked eye, and artifacts with hand-applied coloring may be particularly vulnerable to optical changes or transfer of the color. Cleaning of all such delicate objects should be left to a professional conservator.
Dry removal of sticky deposits and surface accretions can be considered a kind of surface cleaning. Sticky tape adhesives damage paper and can create the physical hazard of bonding papers to adjacent papers and enclosures. Some old tapes fall away as they age and leave thick, hardened adhesive residues. These residues, although unsightly, are not an immediate hazard, and they can be addressed only by a professional conservator. In fact, tape removal itself is difficult and should be referred to a professional conservator. Sometimes, however, tape adhesive absorbs underlying text or image and the tapes cannot be removed at all. Insect excretions and rust deposits, such as those left by rusted paper clips, are not only disfiguring but also the source of ongoing damage to the paper. It is a good idea to remove these deposits when feasible.
Closed books on the shelf normally present an effective barrier to the entry of air-borne dirt into the text, but if the pages are cockled, the boards are lost, or a variety of other circumstances permit the entry of dirt, it will normally accumulate along the unbound edges of the pages. Coarser dirt may accumulate in the gutter (binding) edge of the pages. Both of these situations may call for surface cleaning.
Moldy materials are obvious candidates for surface cleaning, which may be all that is possible or necessary. Mold activity should first be stabilized by providing the affected materials with a prolonged environment of low relative humidity, generally below 50 percent, so that the mold goes dormant. Mold removal is a delicate procedure and requires careful work hygiene to avoid spreading contamination as much as possible. Mold can also affect the health of personnel, so protective equipment such as respirators, gloves, and fume hoods should be used when removing it. Therefore this work is probably best left to a professional conservator, or in the case of large quantities of moldy office or archival papers or nonrare books, brought to a commercial enterprise that offers disaster-recovery services.
Several erasing compounds on the market are primarily intended for use by graphic designers and architects. They come in containers of granules to be sprinkled on soiled drawings, or in cloth bags that leak small amounts of granules as they are rubbed across the surface of the paper. These granules are potentially damaging because they are abrasive and chemically unstable. In the past conservators recommended that practitioners simply clean the paper thoroughly of these granules after using them, but microscopic examination of cleaned test papers has shown that considerable residue of the granules remains embedded in the fiber structure of the paper afterward. Conservators prefer to use granules produced by grinding up vinyl block erasers, available commercially from conservation suppliers. This cleaning agent is less abrasive and breaks down less during use, so it has less of a tendency to leave residues behind.
The erasers used to make these compounds are also sold as blocks, such as the noncolored Eberhard-Faber Magic Rub Eraser and the Staedtler Mars Plastic Eraser. The blocks are sometimes useful for surface cleaning. More commonly used by conservators nowadays, however, are vulcanized rubber dry-cleaning sponges, which were intended originally for soot removal following a fire. The sort recommended for cleaning papers is not the "chemical sponge" because conservators avoid sponges that contain solvents or cleaning agents. The preferred sponges do not leave damaging residues on paper and they are not abrasive. They degrade upon exposure to light and with age, so they should be stored in an air-tight container in the dark.
Creped rubber adhesive pickups are useful for lifting residues of pressure-sensitive tape and other sticky deposits. Scalpels with a pointed tip are good for picking off insect specks, rust deposits, and other small surface accretions.
For all dry-cleaning procedures a clean, soft brush is needed. Brushes intended for surface cleaning should not be used for wet work, and any brushes used on moldy materials should be labeled and kept separately, to avoid spreading mold to other papers.
Before attempting these procedures it would be wise to practice them on expendable objects to test your confidence and comfort level. If unsure of any of these techniques, do not experiment with them on objects of value.
To start work, clear a large, clean, smooth work surface. On it place a large sheet of inexpensive, clean paper that can be changed frequently. Begin cleaning by gently brushing the surface of an object with a soft brush to remove loose dirt and dust. (If this raises dust particles, wear a dust mask!) Under no circumstances should you brush over powdery media such as pastels or charcoal, or over flaking paint or ink. Be careful to avoid enlarging tears by brushing in the direction of the tear. Brush both sides of the sheet. Every few strokes brush across a clean fabric or blotting paper to dislodge dirt from the brush.
Gently rub sticky tape adhesives with numerous extremely short strokes of the creped rubber pickup eraser. This can be time-consuming, but numerous gentle strokes eventually pick up the adhesive without damaging the paper, as fewer, more forceful applications might. The adhesive is picked off the eraser with the fingers.
Pick off accretions such as insect specks and rust deposits with a scalpel tip, and keep a brush at hand to remove dislodged materials. Do not overdo this work; it is better to leave accretions alone when more aggressive efforts to remove them may inadvertently make a hole in the paper. For the same reason it is best to avoid inclusions embedded in the paper. These are specks of metal that were in the paper when the sheet was formed, and that became visible as they oxidized over time.
Next, local deposits of grime may be reduced by gentle rubbing with a vinyl block eraser. (Block erasers are not appropriate for cleaning larger expanses of paper.) Rub in short, meandering strokes to avoid setting up a pattern of erasing marks, and check periodically with a close sideways examination across the surface to make sure the paper is not being abraded. Never rub over media, whether printed or drawn, and do not persist if no improvement is made. Unfortunately, surface cleaning does not remove aged finger marks in most cases.
Grated/granulated vinyl erasers are effective for overall cleaning of papers, and can be used on most printed surfaces. Pour a small amount of the granules on a small spot in as obscure an area as possible, and gently roll the granules in a circular motion with the fingertips. If this is effective the granules will rapidly become dirty. Satisfy yourself that the granules are lifting nothing but dirt, then carefully brush them away. After determining that this cleaning will make a worthwhile improvement, proceed with the rest of the surface. Remember, however, that cleaning that is effective in only one area is counterproductive if it leaves the remainder of an object looking dirtier in contrast.
A bit more thorough cleaning can be achieved with a vulcanized rubber sponge. This tool is gentle, provided the practitioner is careful, but it is still not normally recommended for use on design areas. Conveniently, the margins of an object often permit more thorough cleaning, and here successful cleaning usually has the greatest visual impact. Sponges can also be used on the reverse to reduce dirt that might otherwise be transferred during handling, but take care to avoid notations on the reverse that might have historic significance. Again, rub gently and in random directions if there is any sign of setting up a pattern on the surface of the paper. Soiled sponge surfaces can be cut away to expose clean surfaces and prolong the usefulness of the sponge. Do not use any moisture with these sponges. Finish by brushing the paper with the soft brush to remove any crumbs from the sponge.
Granules should not be used in books, as they are sure to become trapped in the gutter despite the best efforts to brush them away afterward. The soft brush is the best tool for removing accumulated gutter detritus, and vulcanized rubber sponges serve best for removing grime along the other edges. When leafing through an old book, whether to surface-clean or just to check for the need to surface-clean, be sure to support the book on an appropriate cradle or foam book wedges to avoid unduly stressing the binding. For further information on cleaning books, consult the NEDCC Preservation Leaflet "Cleaning Books and Shelves."