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Maine State Archives
Guidelines for Restoration and Preservation of Documentary Papers, Maps, Books TABLE OF CONTENTS INTRODUCTION PAPER CAUSES OF DETERIORATION TEMPERATURE HUMIDITY FLATTENING FOLDED OR ROLLED MATERIALS MOLD ATMOSPHERIC POLLUTANTS LIGHT ACID MIGRATION INSECTS AND RODENTS PROPER BOOK HANDLING CLEANING BOOKS LEATHER BOOKBINDING'S CLEANING LEATHER BOOKBINDING'S TREATMENT WITH POTASSIUM LACTATE TREATMENT WITH NEAT'S-FOOT OIL AND LANOLIN REPAIRS INGREDIENTS TO MAKE THE GELATIN MIX PREPARING THE PASTE USING THE PASTE AND TISSUE TO REPAIR TEARS PROTECTIVE ENCASEMENT FIRE EMERGENCIES SOURCES
Introduction
Since most of the information on the processes involved in the care of documentary papers, books and maps is of a technical nature, scattered through many works and not widely available, the Archives former paper conservator, Loyd D. Clark, Jr., has brought together in convenient form the basic principles and simple processes that can be safely used. In providing these guidelines, which are not intended as all- inclusive, Mr. Clark noted: "By following the procedures outlined in the several sections, much can be done to properly restore materials to usable condition without causing further damage. A word of caution however: the methods should not be applied indiscriminately to everything. A professional conservator should be consulted when dealing with documents of great value or material in an advanced stage of deterioration. Without such consultation it is better to do nothing than to do the wrong thing." This edition was revised by David Anderson and Susan Rogers of the Archives Staff, following Mr. Clark's earlier 1982 edition.Paper
Paper is an organic substance composed of cellulose fibers from plants; because of its organic nature, paper will deteriorate if not properly made or stored. Papers made in the period beginning with the Twelfth Century and ending with the middle of the Nineteenth Century were strong and durable; and many books and documents published prior to 1850 are still in excellent condition. Modern paper is generally made from wood fibers which have been mechanically ground for newsprint or chemically purified for books and writing papers. Finer papers also contain cotton or linen fibers. Most modern papers, unless designated as acid-free or permanent/durable, have an expected useful life of less than 50 years.Causes of Deterioration
The rapid deterioration of modern papers results from the use of acids which break down the cellulose fibers into ever shorter segments, thereby weakening the paper. The acid deterioration may be accompanied by yellow or brown discoloration, a condition brought about by the use of alum-rosin compounds as sizing agents which generate sulfuric acid when atmospheric moisture is present. The use of groundwood or unpurified wood fibers rather than chemically purified pulp is another factor in modern paper deterioration. The lignins or "glues" which hold the fibers together as wood degrade to form acids which weaken the paper. Although most papers contain some unpurified wood fibers, the most common example of groundwood paper is newsprint. Other factors influencing paper deterioration are: atmospheric pollutants such as sulfur dioxide, nitrogen dioxide, and ozone; the invisible radiation of sunlight and fluorescent light; the short wave lengths of visible light; the growth of microorganisms such as mold and bacteria; and insects and rodents which feed upon the paper.Temperature
High temperatures, combined with high humidities, facilitate the acidic reactions which contribute to the deterioration of paper. Thus, the life of paper can be extended by lower storage tempera tures; theoretically, the useful life is almost doubled at each 10-degree Fahrenheit decrease in temperature. A constant storage temperature of 68-degrees Fahrenheit is consid ered ideal, being high enough to be comfortable to workers and low enough not to damage materials. Widely ranging fluctuations in temperature are extremely damaging, as are high temperatures. Therefore, papers and books should never be stored in attic areas where wide fluctuations are common, and temperatures approaching 150-degrees Fahrenheit may occur on summer days.Humidity
Relative humidity (rh) is the relationship between the amount of water vapor in the air and the amount that would saturate the air (100% rh) at a given temperature and barometric pressure. High relative humidities (in excess of 68%) cause the swelling and warping of paper fibers and hasten acid deterioration. Also, high humidities in the presence of metal staples and paper clips will cause rust stains, even though no actual water damage occurs. Low humidities (below 40%) will cause paper to dry out and become brittle; often in this range, fragile pages will stick together as a result of static electricity, and may tear if care is not exercised in turning pages. Seasonal fluctuations of less than 10% in winter to more than 90% in summer are damaging to paper materials. Modern book papers should be stored at 40% to 50% rh; leather bindings, at 45% to 55% rh; and vellum or parchment, at 50% to 60% rh. Overall, a good compromise is storage at 50% rh, with an acceptable range of 45% to 60% rh. Fluctuations within the range should be kept to a minimum. Humidity levels in a small storage area can be maintained with a small air conditioning unit, a dehumidifier and/or a humidifier. Basement storage areas are generally not desirable due to possible flooding and ordinarily high humidity levels. As inexpensive commercially-marketed gauges are frequently inaccu- rate, the relative humidity of the storage area should be monitored with a dry-wet bulb thermometer or a sling psychrometer. Both record the temperature difference between a dry bulb and a wet bulb thermometer; the evaporation which occurs around the wet bulb thermometer is directly related to the humidity. A chart or sliding chart rule gives the relative humidity for the given conditions.Flattening Folded or Rolled Materials
Papers which have been folded or rolled for long periods are often dry and brittle; and flattening may cause breakage of the cellulose fibers with permanent paper damage. Restoring moisture to the paper will relax and soften the fibers allowing the paper to be flattened much more easily. The best method of restoring moisture is to place the paper in an area of high humidity (around 100% rh) for one or two days. The documents may be sealed in a container with water or with a wet sponge in a manner that the water is not in contact with the material. A new plastic garbage can serves as a useful container, with a pan of water on the bottom and, above, tiered shelving of plastic screening on which to place the materials. The paper must not be in contact with any condensed water which forms on the wall of the container. Alternatively, the folds or the rolled materials may be wiped with a DAMP sponge. The danger in this method is the possibility of smudging inks or colors which are not water-resistant. With either method, once the paper has absorbed moisture, flattening will proceed more easily. Once flattened, the paper should be allowed to dry under pressure. Individual pages or small groups of pages should be separated with white blotter paper or cardboard (chipboard), then covered with a piece of plywood weighted down evenly with books or some other heavy material for one or two days until dry.Mold
Storage of materials in the suggested ranges of temperature and humidity will prevent the growth of mold. However, mold spores are always present in the air and in the dust that settles on documents; and, if the recommended conditions are not maintained, the danger of mold growth and damage to documents exists. A relative humidity of 70% combined with high temperatures encourages the growth of mold or mildew, although some molds will grow at temperatures as low as 40- degrees Fahrenheit if the humidity is high. Stagnant air conditions also favor mold or mildew attacks. Once started, mold is difficult to control and serious damage may occur before the condition is detected; prevention is far easier than correction. The environment should be monitored on a regular basis to avoid the conditions favoring the growth of mold. In the initial stages, mold growth may be little more than a nuisance. The visible evidence can be brushed away, and the item can be stored under recommended conditions without further concern. In later stages, mold will digest the material upon which it grows, resulting in staining (foxing) and loss of strength of the material.Atmospheric Pollutants
Damage from air-borne pollutants is most evident in old books and in stacks of old papers, where the edges of pages are discolored from acid deterioration while the center portions remain almost white. Certain gases such as sulfur dioxide, hydrogen sulfide and nitrogen dioxide originate from burning fossil fuels and are most serious in industrial areas. As large and expensive filtering devices are necessary for removal, no economical means of protection is available for the small collector. Some of the compounds are not dangerous until combined with other compounds to form acids; for example, sulfur dioxide is catalyzed by other airborne compounds to form sulfur trioxide, which unites with water vapor to form sulfuric acid. Ozone, a pungent gas generated by the interaction of sunlight and nitrogen dioxide from auto exhaust and one which is also prevalent around electric motors and after thunderstorms, causes the oxidation and consequent embrittlement of paper. As dirt and dust carry absorbed pollutants which can be abrasive to books and paper, air in a storage room should be filtered, with frequent changes of filters in the system. Where filtration is not possible, objects can be stored in closed containers; if used, plastic bags should not be tightly sealed. Exhibit cases which are sealed against dust and dirt should provide air circulation through filters. As stagnant air increases the possibility of mold growth, any material stored in closed containers should be checked frequently. Also, the area should be cleaned and vacuumed regularly to eliminate dust and dirt buildup on any materials.Light
Exposure to the ultraviolet rays of sunlight and fluorescent light causes the rapid deterioration of paper, leather and fabrics; similar, but less severe deterioration will occur with exposure to visible light, the rays at the red end of the spectrum being less damaging than those at the blue end. The visible effects of light include: the bleaching or fading of paper; and the yellowing or browning such as rapidly occurs with newsprint. Not immediately visible is the breakdown of fibers into smaller units, causing the paper to disintegrate. Unfortunately, the reactions continue after the source of the problem is removed, although at a slower rate. Other factors being equal, paper stored in complete darkness will last far longer than that which is subjected to light. However, as totally dark storage is not usually practical, other precautions must be taken. Paper should never be stored in direct sunlight or under unshielded fluorescent tubes. Special ultraviolet-filtering materials, such as UF-3 Plexiglas or Acrylite OP-2, may be used to shield windows or fixtures. Valuable documents should be deacidified and alkaline-buffered by a competent paper conservator, and stored in acid-free file folders in an enclosed container. If a document is to be mounted for display under ultraviolet- filtering material, the document should be matted with acid-free board, preventing direct contact with the protective filter; the latter contains a yellow dye which might otherwise discolor the document. Even when shielded, the document should be hung to avoid sunlight and fluorescent light. Frequently, display cases will contain fluorescent lights which are damaging to the displayed material unless shielded with special plastic sleeves of ultraviolet-filtering material which slip over the tubes. Although these shields are expensive, their use is essential as the displayed items are close to the light source and thus receive a high amount of ultraviolet radiationAcid Migration
Failure to use acid-free folders, matting boards and materials (see SOURCES) for records storage will result in acid migration, the movement of acids from acidic materials to those which are less acidic. A familiar example of acid migration is the brownish discoloration commonly observed where newspaper clippings have been stored in old books.Insects and Rodents
Insects and rodents are attracted by the cellulose of the paper, the proteins and carbohydrates of gelatin sizing, glue, paste, leather and other organic substances. The most certain way to avoid insects and rodents is to practice good housekeeping: keep food away from the storage area, screen windows, and kill any insects or rodents observed. As a further precaution against insects, one can place small open containers of paradichlorobenzene (the active ingredient of moth crystals) on bookshelves. Paradichlorobenzene is a poison and must be placed beyond the reach of children! If insects are found in stored documents, one can place them in a covered container with paradichlorobenzene for three weeks, an ample time to eliminate insects and their eggs. Paradichlorobenzene is available in drug, discount and general stores under various trade names. The material readily vaporizes and requires periodic replacement. Silverfish may be eliminated with a sweetened mixture of 1-3/4 cups wheatflower or oatmeal ground to flour, 1/4 teaspoon sodium fluoride (available in drug stores), 1/2 teaspoon granulated sugar, and 1/4 teaspoon salt; once mixed, the powder can be placed in shallow cardboard boxes loosely covered with crumpled sheets of paper. The mixture is ample for several good sized rooms, and the boxes may be placed in areas where silverfish are known to occur. Wheat flour or Oatmeal (ground to flour) 1 3/4 cups Sodium fluoride (available in drug stores) 1/4 teaspoon Granulated sugar 1/2 teaspoon Salt 1/4 teaspoon Mix the ingredients thoroughly and it is ready to use. This powder should also work on various other insect pests. Sprays should be avoided because of the chance of staining materials.Proper Book Handling
Never remove a book from the shelf by pulling upon the headcap. Push back a few books at either side and firmly grasp the sides of the selected volume. Books leaning to one side will be damaged along the spines. Books should stand upright, and, in the absence of book ends, should be supported by lying several volumes flat against the standing volumes. Large books should be stored flat.Cleaning Books
Using a prepared cloth such as "One-Wipe" or a clean cloth treated with "Endust" will reduce the spread of dust. Take one book at a time, and hold the book firmly closed to prevent dust from entering the pages. With the spine up, tip the head forward and down; dust the top of the pages thoroughly, stroking downward; then dust all other surfaces.. Certain erasers may be used to clean book covers and any surface dirt from pages. However, in cleaning paper, a soft bristled brush should be tried before resorting to erasers. Erasers, in order of decreasing abrasiveness, are Faber's "Pink Pearl and Magic Rub" and art gum erasers. For paper, the "Opaline" Dry Cleaning Pad or Dietzgen's "Skum-X" can be used; using the latter two, sprinkle eraser crumbs over the soiled area and gently rub in a circular motion with the flat of the fingers. To lessen the likelihood of damage, work from the center of the page to the edges. Remove all eraser crumbs when finished. If any doubt exists about the strength of the paper, leave the page alone. Care must be exercised to avoid damage to the gold stamping of titles on book covers which can be ruined through improper erasures. The erasers referenced above are available through stationery or drafting supply stores.Leather Bookbindings
Factors influencing the deterioration of leather are the quality and age of the original skin and the tanning process by which the stability of the leather was achieved. Leather produced before the 17th Century was of fine quality and very long-lasting; whereas that produced since the late 17th Century frequently shows rapid and severe degradation. The older vegetable tanning processes (the type usually used for bookbinding) may have left protective or buffering salts that reduced deterioration; apparently, these salts are missing from modern leathers. Strong mineral acids from air pollutants and sulfuric acid left by the tannage process contribute to the destruction of leathers. Relative humidities below 40% cause leathers to dry out and deteriorate; on the other hand, high humidities and high temperatures speed up the chemical deterioration of leather. Light, even indirect sunlight, will produce fading or darkening of dyes in leather; valuable bindings should be protected in boxes made from opaque and inert materials. The flexibility and suppleness of leather depends on the sliding action of fibers which can become dried out if not lubricated. Thus, an important step in the preservation of leather is replacement of those natural oils which may have oxidized. In some cases before lubrication, the leather may require rehumidification to restore moisture content. The sulfuric acid used in processing modern leathers is extremely difficult to remove; also, in the process, the natural buffering salts are washed out of the skin. The lost salts can be replaced with potassium lactate (see SOURCES) which serves as a buffering salt and neutralizes any strong mineral acids. Go to Part 2 Return to the Maine State Archives home page. Return to the Department of the Secretary of State home page.