The Enemies of Paper

Paper is fragile. Although it can last for centuries if properly made and cared for, it is highly susceptible to damage by environmental conditions, by insect pests, and by man. But dangers may also come from within, for paper may begin with flaws.

INHERENT FAULTS
Even the finest handmade papers are sometimes disfigured by stray pieces of wood or rusty metal, marks from the ropes in the drying loft, or buckling caused by hasty drying and curling. Much more serious defects can result from the various technical "improvements" mentioned earlier. Machines were devised for preparing pulp composed of shorter and shorter fibers, which made a weaker sheet of paper. Chemicals used to make a whiter sheet from a larger range of raw materials were so harsh that strength was further reduced. Incomplete washing and the addition of still other chemicals, particularly alum, left dangerous residues that, like an invisible time bomb, ensured eventual destruction.

Of course, there are now many types of paper that are by nature short-lived, that are born to die. The newspaper or paperback book, for example, will not be in readable condition for more than a couple of decades, perhaps less. But then, should they be? On the other hand, many book publishers and libraries have awakened to the fact that, because so little attention has been paid to the built-in dangers to paper, the majority of books printed in the first half of this century--books that should last--will probably be unusable by the year 2000. This alarming situation has impelled modern technology to answer the question of what constitutes paper permanence, so that one can at least choose whether the paper to be used will last long enough to suit the purpose. Thus, the present situation differs from that in the fifteenth century in that permanence in paper is now a matter of choice rather than of circumstance.

Use of a permanent paper is half the battle of preservation. If publishers want their product to last, they should select paper with the appropriate specifications. Artists should seek out the many fine all-rag papers available if they want their work to outlive them. Art collectors should take care to see [p. 13] that only all-rag mats and acid-free papers are used in framing their pictures [see "Matting and Framing"]. Archivists, librarians, and curators should familiarize themselves with the acid-free papers and storage materials existing today.

Handling - Most damage to paper caused by man could be avoided with just a little extra care and common sense. The standard rules of handling are as follows:

1. Use clean hands to handle books and pictures.

2. When lifting matted or unmatted pictures, use two hands to keep from bending, creasing, or tearing them.

3. Unmatted pictures should never be stacked directly on top of each other but should be separated by a smooth, nonacid cover tissue.

4. For optimum protection valuable pictures should be matted rather than left loose. Less valuable pictures or documents can be kept in acid-free folders or envelopes.

5. Be careful not to touch or drag anything [the corner of another mat, for example] across the surface of a picture. Mezzotints, pastel drawings, and silkscreen prints are particularly vulnerable to surface damage.

6. Never use pressure-sensitive tapes [Scotch tape, masking tape, etc.], gummed brown wrapping tape, rubber cement, synthetic glues, or heat-sealing mounting tissue on any picture that is to be preserved.

7. Pictures glued down on old boards should be handled with as much care as any unmounted, brittle picture. The backing gives a false sense of strength, which may put one off guard.

8. Matted pictures should be protected with cover tissue when not in use. For temporary display or protection, the entire mat can be wrapped in flexible plastic sheeting [Mylar] and secured with tape on the back, but because of its inherent static electricity, this material should never be used on pictures with fragile pigment, such as pastels or charcoal drawings.

9. Open a mat by the outer edge, not by inserting a finger through the window and lifting the inner edge.

10. Pictures in mats or folders can be stored in drawers or slander boxes. [p. 14]

11. To carry, mail, or ship loose pictures, pack them flat between stout boards, not in a roll.

ENVIRONMENT
Humidity - The chief danger of excessive humidity is the growth of mold. Since mold cannot grow unless the humidity exceeds seventy percent, preventive measures must include keeping the humidity below that amount. Air conditioning or dehumidifying machines are the answer in most climates and damp buildings. For airtight containers and exhibition cases silica gel, a dehumidifying agent, may be helpful [see Nathan Stolow, "The Micro-climate: A Localized Solution," Museum News, 56, no. 2, 1977]. When hanging or storing pictures beware of dampness on outside walls in stone houses and in basements and cellars. Houses closed up for an extended length of time may become excessively humid and should be aired periodically and checked for signs of dampness or musty odors.

To illustrate the damaging effects of poor ventilation we mention a colored woodcut recently brought into the Conservation Laboratory that had mold growing not only inside its frame but also all over the outside. It had hung in a summer home that had been closed during the winter. And as a further example, two fine eighteenth-century engravings were treated for mold growth that had resulted from five years' storage in a warehouse without adequate circulation of air.

Mold growth in paper often shows up as dull rusty patches that discolor the sheet. This is called "foxing" and may be caused by the chemical action of mold on metallic salts often present in paper [Figure 1]. Mold feeds on sizing and paper fibers and thereby weakens the sheet. It grows easily on pastels, which contain good nutrients for mold in their binding media. Foxing is the usual result of prolonged, high atmospheric humidity, but if water itself seeps into the picture or book, rampant proliferation of mold may completely envelop the object. First-aid treatment is to remove the object to a dry environment. Open the frame or spread out the pages so that air can circulate freely to the infested areas. Expose to direct sunlight for about one hour to kill the mold or, preferably, place in a closed container with some crystals of thymol, a fungicide, for two or three days.

Small sachets or dishes of thymol crystals placed in bookcases or storage containers can help to prevent mold. Librarians and art collectors may also want to construct a thymol cabinet designed specifically for treating mold. It [p. 15] should have a metal floor on which the thymol crystals are placed and several racks or shelves on which pictures and books can be spread out to allow the thymol fumes to permeate the paper. The metal floor is gently warmed from below by low-wattage [forty-watt] bulbs, which are turned on every day or two for about an hour to make the thymol crystals volatilize more effectively. The placement and power of the bulbs should be adjusted so that the metal floor never feels hot. If evaporation occurs too quickly, the thymol vapors may saturate the air in the cabinet, recondense as small oily droplets, and form spots on the pictures. Since thymol softens oil paint, the inside of the cabinet should be left unpainted. For the same reason pictures painted in oils should never be treated with thymol.

Since thymol is volatile, it offers no permanent protection against recurrence of mold if an object is returned to a humid environment. For example, the surface of a pastel painting recently brought into the Conservation Laboratory was covered with mold. A note on the back of the frame indicated that the pastel had been treated for mold fifteen years earlier, and the owner revealed that after treatment it had been put back in the very same place as before, on the damp outer wall in an old stone house; thus it had contracted another bad case of mold.

In summary, the rules for guarding against mold are as follows:

1. Keep the humidity below seventy percent; about fifty percent is ideal.

2. Do not store pictures or books in damp cellars or basements.

3. Avoid hanging pictures on the outside walls of a house, especially if they feel cold or damp.

4. Never frame pictures directly against the glass [see "Matting" and "Framing". To do so invites damage by mold growth or condensation of moisture.

5. Clean bookshelves, frames, and storage areas regularly, as dust contains a large amount of airborne mold spores.

6. Good circulation of air reduces chances of mold growth. Circulation of air behind a frame is improved by attaching small pieces of cork or wood to the lower two corners to keep the frame away from the wall.

7. Never store pictures or books directly on the floor. Raise them on supports to allow circulation of air.

8. Avoid leaving books and pictures in a closed room or house for extended periods of time without providing some means of circulation or dehumidification. [p. 16]

9. Fumigate infested books, pictures [except oil paintings], storage containers, and bookcases with thymol fumes to kill mold, and be sure to correct the conditions that originally caused the mold growth.

Light - Of all the external forces that can affect paper, light--perhaps because it is so much a part of our everyday experience--is often the most ignored and misunderstood.

In times past, prints and drawings were traditionally kept in books or albums as illustrations to texts and shown now and again in the parlor to gatherings of family or friends on Sundays or special occasions, much in the way albums of snapshots are shared today. Life styles have changed, and today the print or drawing is made to serve as a decoration on the walls of a house, office, or gallery, a function that often exceeds its original purpose. Furthermore, the growing interest in art has not only spread ownership of prints and drawings, but has also augmented the number of exhibitions and hence the accessibility of these works of art. The net result is a drastic increase during the last several decades in the danger of damage resulting from overexposure to light.

Collectors, rightly concerned with this hazard, often ask conservators whether fading can be stopped by keeping watercolors, drawings, or colored book bindings in subdued light. Unfortunately, and to their surprise, the answer is "no." It must be remembered that all light fades works of art on paper; less light means only less fading. Pigments used by the papermaker to tint his product or by the artist to create his image do not automatically stop fading when the light drops below a certain level [see Figure 2]. And fading is not reversible. Placing a work of art on paper in darkness merely halts the process and does nothing to promote recovery or rejuvenation.

How much light should be used for viewing works of art on paper? What minimum amount of light does the human eye need to perceive all colors in their proper relationships? The answer is one of degree. Anyone who takes a walk by moonlight can verify that when light is at an extremely low level the eye loses all ability to perceive colors and can only distinguish tonal, or black and white, values. Therefore, one can only conclude that there must be sufficient light for good viewing, but any excess, which will hasten fading, must be avoided at all costs. An optimum amount of light is five footcandles, which corresponds roughly to the output of one 150-watt reading lamp at a distance of three or four feet. In other words, use the same amount of light for viewing works of art on paper as is required for casual reading. [p. 17]

Bear in mind that the human eye is a poor judge of light quantity because it adapts so easily to major changes in intensity. The eye needs mechanical assistance to make an objective determination of light quantity. This can be accomplished with some of the older photographic light meters, such as the Weston, which are calibrated in footcandles. Follow this procedure. Take a sheet of white blotting paper or other similar unglazed white paper, at least one square foot in size. Put the paper in the position that the picture is to occupy and, following the manufacturerÍs directions for using the meter, make a grading of the light reflected from the sheet of paper. The proper amount of light is now determined [See "Materials and Services" for two other types of meters that measure footcandles directly.]

The next step is to guard against unnecessary exposure. Museums and historical societies control exposure by various means. It is their practice for example, to keep delicate watercolors and documents with fading ink in storage for viewing only by appointment. They display them in rooms lit artificially only during well-defined hours. They install them in cases protected with fabric coverings, which the visitor himself can remove and replace. In the nineteenth century, some Victorian frames for watercolors were equipped with a small curtain, resembling a window shade, that would roll up inside the molding when raised to view the picture.

Most large museums rotate selections from their holdings so that an object is never left on view for more than a few months at a time, a practice which even the modest collector might well emulate. Simply changing the position of the pictures in your house once every year or so will not only diminish the possibility of their fading but will also place them in a new perspective that will enhance enjoyment of them. The established collector might even consider the possibility of storing a certain percentage of his collection on a rotating basis.

Avoid hanging pictures or placing bookshelves or glass-fronted bookcases on a wall directly opposite windows, since the light is likely to be greater there than anywhere else in the room. Translucent curtains or louvered blinds can be used to moderate or redirect the bright light of day.

Pictures should, of course, never be hung in direct sunlight. Even reflected [p. 19] or indirect daylight, however, carries a danger in addition to intensity, for it is a source of ultraviolet light, which, though invisible, is even more destructive than visible light. Ultraviolet rays accelerate fading and even cause deterioration of the paper itself. Watercolors, prints, drawings, and books should therefore never be exposed directly to these damaging rays. Fluorescent lights are a potent source of ultraviolet light and should always be covered with cylindrical plastic sleeves that filter out the dangerous radiation. Alternatively, ultraviolet-filtering acrylic plastic may be substituted for glass in a picture frame [see "Matting" and "Framing"].

Heat- Do not expose pictures and books to heat, since high temperatures accelerate the deterioration of paper. Do not hang pictures over a radiator, heating register or air duct. The enticing spot above the fireplace is doubly bad as a place to hang pictures, first, because of heat, and, second, because soot and gummy residues produced by the fire adhere to the glass and obscure the picture.

Air Pollution - Urban areas are antipaper. The city dweller should realize that a polluted atmosphere is one of the dangers that threaten the longevity of paper and the permanence of works of art on paper. The most harmful contaminant in the atmosphere is sulphur dioxide, a gas produced by combustion of fossil fuels like coal and oil; it is a major constituent of smog. Sulphur dioxide attacks paper and causes discoloration, embrittlement, and eventual disintegration of the paper fibers. It is absorbed by the paper and converted into sulphuric acid, a particularly strong acid that does not evaporate and leave the paper even after it has been removed from contact with the gas. Severe brown stains caused by this destructive pollutant are often seen on framed pictures that have been partly or entirely exposed to the air by lack of adequate backing [see Figure 3]. Sulphur dioxide also robs leather bookbindings of their strength and pliability and can eventually reduce them to mere powder. At the turn of the last century library holdings were severely damaged by the high concentration of sulphur dioxide produced by the use of illuminating gas.

Certain artist's pigments can also be affected adversely. Ultramarine blue, for example, which is often used in watercolor painting, can be completely destroyed long before the paper itself has been even moderately discolored. [p. 20] White lead, encountered more often in oil paintings but sometimes used as a highliht or as body color in wash drawings or watercolors, reacts with sulphur dioxide to form lead sulphide and darkens to a dirty gray or sooty black, thereby destroying the tonal range of the picture.

Air pollution seems to be an inescapable hazard of urban life. The only sure defense, short of removing the paper to the relatively unconataminated air of the suburbs or the country, is to install air conditioning. The restorer can help to minimize the effects of pollution by washing or deacidifying paper that has been exposed too long to city pollutants. Protectin of framed pictures with all-rag board, front and back, plus a backing large enough to cover the entire mat will help to minimize danger from a polluted atmosphere. The new technology is also introducing into paper manufacture alkaline chemicals which aid in neutralizng the damaging effects of pollutants. Acidic substances which attack and destroy leather bookbindings can be neutralized by applying a solution of potassium lactate. [For directions on applying this solution see Carolyn Horton, Cleaning and Preserving Bindings and Related Materials, 2nd ed. rev., Chicago, 1969.]

Insects - The most common insects that threaten paper are silverfish, termites, cockroaches, and woodworms. SIlverfish are silvery, or pearl gray, insects with three tail-like appendages; they are often discovered when books, papers, or frames on the floor are picked up or suddenly moved. They prefer warm, damp places, shun the light, and move so quickly that detection is difficult, so that they may cause considerable damage before they are noticed. A serious threat to books, they are equally damaging to works of art on paper. They will eat their way through pictures to get at flour paste and glue sizing but also enjoy bleached wood-pulp paper [see Figure 4]. A picture about 16 by 20 inches in size was brought into this laboratory for treatment; its surface had been almost entirely devoured by silverfish, so that scarcely a trace remained of the original image.

Although termites and woodworms are commonly thought of as enemies of wood alone, they will devour virtually anything made of cellulose, including paper. Their winding, branching tunnels can cause considerable structural damage to book covers, frames, and pictures that have been mounted on wooden panels [see "A Note on Restoration"].

Cockroaches inhabit dark, warm, damp places, and usually come out during the night. They cause damage to parchment, leather, paper, fabrics, and any glues or painting media containing sugar. Infestation by these insects [p. 22] is best prevented by regular cleaning and by inspection of the dark spaces behind and beneath books, cases, boxes, and picture frames. Particular attention should be paid to areas such as basements and attics, where traffic is minimal, and which tend to be damp or dark. Use of aerosol or powdered insecticides is necessary if signs of these insects are present. [For further information see Philip R. Ward, Getting the Bugs Out, Victoria, B.C., 1976.]