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The preservation and restoration of paper records and books
Carmen CRESPO and Vicente VINAS
INTRODUCTION
This study examines the current methods of conserving paper records and books in archives and libraries. Reference is made to the fairly ample, if scattered, literature and the work of various laboratories, particularly that of the Centro Nacional de Conservacion y Microfilmmacion Documental y Bibliografica de Espana which has devoted its energy over the past 12 years to the conservation of this part of the national heritage.
In conservation as such, we distinguish two distinct but complementary areas: the first includes all methods designed to avoid the deterioration of records (preventive or preservative methods); the second involves the direct treatment of items that have suffered damage or deterioration (curative measures and restoration).
Ideally, conservation policy should include preventive measures that obviate the need for the second set of measures. 'Prevention is better than cure' applies to this part of our cultural heritage no less than to health.
Without doubt, the correct application of either method calls for accurate knowledge of the material and structural qualities of the support (paper), of the graphic elements sustained by it (inks) and of their behaviour over various periods of time.
Thus the study of the environmental (external) as well as the inherent (internal) causes and effects of the deterioration of paper is of great importance to the archivist
Some of these topics are not treated as fully as others in this study. The characteristics of the supporting and the sustained media (paper and ink) and the causes of their deterioration will receive relatively brief attention and will largely serve as an introduction to the preventive and curative measures that make up the meat, the crux of this study. There is quantitative difference between preventive and curative methods and this paper focuses special attention on just one: the curative side. Its complexity and diversity are such, that there is still a great deal of uncertainty about it, not only among laymen but also among experts. The whole subject of restoration is in a state of constant flux, as technical and scientific innovations follow one another in quick succession. The preventive side, by contrast, is not only less controversial but also much less variable.
We hope that this study will be of use to all concerned with the preservation of records and books and especially to archivists and restorers.
GUIDELINES
1. Paper as a Support
Paper is the most widely used support of documents stored in archives and libraries. We distinguish two main periods in the manufacture of European paper. During the first, which continued until the middle of the nineteenth century, the basic materials were rags of vegetable origin (linen, hemp, cotton). The resulting paper was composed of cellulose, a substance found in plant fibres, a sizing of vegetable or animal glue, and a small reserve of alkali. The water molecules incorporated in the pulp during the process of paper making form bonds with the hydroxyl radicals of the cellulose, and hence serve as bridges (hydrogen bridges) between contiguous long-chain cellulose molecules.
Paper manufacture from rags was mechanized at the beginning of the nineteenth century and led to the production of continuous webs of paper (mechanical paper). In the eighteenth century, the growing demand for paper had already imposed the use of other than white rags for paper production. Chlorine compounds had then to be introduced as bleaching agents and natural sizes began to be replaced with a chemical size, namely alum, which unlike the natural product is added to the pulp before the formation of the paper. Both types of size cause acidity in the paper and decrease the durability of the fibre (sections 1.1-1.2.1.2, pp 3-6).
Wood largely replaced rags in the production of paper in about the middle of the nineteenth century. Depending on the method of production, the pulp is called mechanical, chemical or semi-chemical. Paper made from mechanical pulp retains all the impurities of the wood.
- Paper made from chemical pulp is obtained by treatment of the cellulose with various chemicals that eliminate the non-cellulosic elements of the wood. The resulting pulp is of poor quality, because of the presence of alum rosin and chlorine residues. At the end of the 1950s, permanent durable paper was introduced. Unlike traditional paper, obtained from wood, this paper is alkaline (section 1.2.2-1.2.2.5., pp 5-9).
Synthetic compounds such as polyesters are currently being used in the manufacture of paper for drawings and plans. Their inertia towards external agents and their physical resistance could make them the paper of the future (section 1.3, p.9).
2. Inks
Inks are substances suitable for writing, printing or colouring. Their basic constituents are: colouring matter (dyes and pigments) and adhesives. Some inks contain mordants, chemical substances with the property of fixing the inks to paper and hence replacing the mechanical effects of adhesives (sections 2.2-2.2.1.2, pp 11-12).
Carbon-based ink is stable: it neither changes chemically nor attacks the paper, though it can be affected by losses in the mechanical qualities of the adhesive.
Metallo-acid inks include a dye composed of a metal and an acid which acts as an oxidising agent and mordant combined. The most important of these inks are the ferrogallic or ferrous types. Also included in the metallo-acid group are logwood, alizarin and vanadium inks.
The original aniline inks were very sensitive to light. Today they are of better quality and much more stable (sections 2.2.2-2.2.2.1, pp 12-20).
Typographic inks differ from calligraphic inks in that the watery solvent normally used for the latter is replaced with an oil substance (varnish) in the former. The type of varnish used and its combination with various solvents (driers, thickeners, etc.) determine the suitability of such inks for particular printing techniques. The introduction of synthetic dyes, especially aniline, has greatly complicated the identification of inks (section 2.2.2.2, p.l6).
3. Causes and effects of the degradation of paper
The causes of degradation can reside in the paper itself (internal causes) or in the environment (external causes). The most damaging internal causes are found in paper made from wood (lignin, alum, rosin, chlorine). Inks and metallo-acids must also be counted among the internal degrading agents of paper (sections 3.1-3.2.2, pp. 21-23).
External degradation can be mechanical, environmental, chemical or biological. There are three environmental factors that affect the conservation of paper: humidity, temperature and light. An excess of moisture softens the size and leads to the formation of acids derived from salts and other products used in the manufacture of paper or ink. Sudden and frequent changes in temperature and humidity subject paper to great strains that may rupture its fabric. The most dangerous radiations to which paper can be exposed are those of short wave-length (ultra-violet rays). The atmosphere of industrial areas contains a series of impurities that are harmful to paper (sections 3.3-3.3.3, pp. 23-26).
The most patent destroyers of paper are rodents, insects and micro-organisms. Special mention must be made of termites, wood-feeding insects, that can destroy the woodwork of an entire building and of all the books and documents stored in it.
Micro-organisms (fungi and bacteria) soften paper in the areas they invade, break up the surface sizing, and release pigments in the course of their metabolic cycle (sections 3.3.4-3.3.4.3, pp. 26-28).
It goes without saying that disasters (floods, fires, etc.) can have the most serious effects on documents. Floods can cause inks to run, pages to stick together, paper to rot, and glues to lose their adhesive power. In addition spotting and the growth of fungi is encouraged by the humid atmosphere and by rises in temperature caused by attempts to speed up the drying process. Fire can either mutilate or completely destroy records.
Other causes of deterioration are careless handling of documents, trial-and-error attempts at restoration, and inappropriate reagents used to restore faded inks, etc. (sections 3.3.5-3.3.6, pp. 28-30).
4. Preventive methods of conservation
Preventive methods of conservation aim at creating an ideal habitat for documents, one that puts them beyond the reach of harmful agents. Preventive conservation accordingly is concerned with location, installation, direct physical protection and environmental controls (section 4.1, p.31).
A building intended to house an archive should satisfy a set of general building standards as well as a number of special conditions. Factors to be taken into account in choosing the location of storage area include: orientation of building, segregation from other sections of the archive, the need for fire-proof walls and doors, a rational layout of the surface area, mechanical resistance, protection against environmental dangers.
When old buildings are converted for use as archives, they must be modified to meet all the requirements of conservation.
For archives in tropical countries, construction standards should be particularly stringent; not only the outer walls and foundations but also the doors, windows and roofs should be in keeping with the climatic conditions (sections 4.2-4.2.5, pp. 31-37).
Metal shelving units are highly recommended: in the traditional and also in the 'compact' form they must combine solidity with safety and convenience.
Special storage problems are posed by documents of unusual shape or size (maps, plans, etc.; see sections 4.3-4.3.3, pp. 37-41).
The most usual containers of documents are boxes. Normally they are made of stiff and acid-free cardboard, but inert plastic boxes, which have obvious advantages, are beginning to replace cardboard (4.4-4.4.2, pp. 41-42).
5. Conservation Controls
Closely related to prevention and restoration is the monitoring of factors whose presence or imbalance can impair documents. The chief of these factors are light, humidity, temperature, pollution, biological contamination and fire.
The best natural climate is found in temperate zones where temperature and humidity rarely experience wide fluctuations. Artificial environments (air conditioners) make it possible to regulate humidity and temperature within even stricter limits (sections 5.1-5.1.2.2, pp.43-46).
Atmospheric pollution is caused by the solid, liquid and gaseous waste products of industrial and natural processes. Limitation of biological pollution demands low levels of temperature, humidity and illumination, good ventilation, cleanliness, and periodic checks and preventive treatment.
Fire safety depends on the presence of adequate detection and extinguishing systems. Those based on ionization smoke detectors are the most suitable for archives (sections 5.1.3-5.1.5.1, pp.46-49)
6. Restoration
The restoration of printed documents aims at the recreation of the physical and functional features of paper and ink lost through the passage of time, through handling or through an accumulation of adverse circumstances. Because of its special importance, this type of work must satisfy precise restoration standards which guarantee the preservation of the essence and function of the original documents, respect for their cultural integrity and concern about their transmission to future generations (sections 6.2-6.2.6, pp. 52-54).
The sequence of operations from the time a document arrives in the restoration laboratory to the time it leaves again, constitutes a series of links in a regular chain - the restoration process.
Restoration criteria require, before any restoration work starts, strict control - identification of the item's physical and cultural characteristics - and the opening of a file indicating the treatment given, the methods of application and any other details of general interest. The individual characteristics of each document and the diagnosis of the causes and effects of the deterioration suffered as well as the seriousness of the damage are determined by a series of physical, chemical and biological analyses. The appropriate treatment is determined from the results of the analyses and the value of the document as cultural property (sections 6.3-6.3.2.3, pp. 54-58).
Because of the structural fragility of paper and the instability of the materials it supports, restoration work should be carried out with sufficient safeguards to ensure its complete protection during the time it is in the laboratory or undergoing any other treatment throughout the restoration process.
In systems in which a bath is involved it is necessary to support the document while it is being handled. Inks etc. that are unstable or likely to be soluble must be protected with non-permanent fixatives applied locally or over the entire surface (sections 6.3.4-6.3.4.6, pp.60-65).
Attack by micro-organisms and insects is a common cause of damage. Before introducing a document into a depository, therefore, it is necessary to disinfect it to prevent any likelihood of contagion. The installation and use of a room or area equipped for such a purpose is necessary in any archives or library (sections 6.3.5-6.3.5.1, pp. 65-68).
Patches, incrustrations, dust and dirt are removed by different cleansing treatments: erasers give good results in the removal of solid substances; enzymes are used chiefly to treat damage caused by natural adhesives; and organic solvents are applied to greasy and similar substances. The most stubborn stains can be removed only by bleaching, an operation with harmful side-effects that is advisable only for documents whose aesthetic appearance is important (sections 6.3.6_6.3.6.4, pp. 69-79).
The yellowish colour and friability of many papers may be due to excess acidity, which causes gradual degeneration. Deacidification eliminates this cause and gives the document better protection. The creation of an alkaline reserve with a pH between 7 and 8, according to the type of paper, is recommended as a preventive measure (sections 6.3.7-6.3.7.3., pp. 79-84).
Loss of body can be restored by means of protective and curative consolidating agents. Water helps to bind the fibres together. The most effective consolidating agents are adhesives, basically the increasingly widespread semi-synthetic adhesives (sections 6.3-6.3.8.2, pp.84-87).
Fine tissue-paper of high transparency is used to repair cuts and tears. Gaps or missing areas are repaired by means of grafts, using either the manual or the mechanical process (sections 6.3.9-6.3.10.2, pp.87-90).
Scientific considerations for the restoration of graphic elements demand that falsification of the reality of the mutilated part be avoided. In works of an artistic nature reintegration of the missing area, always using materials and techniques different from those of the original, must be in harmony with the whole (sections 6.3.11.1-6.3.11.3, pp.90-92).
After aqueous treatments documents must be carefully dried in order to reduce the increase in volume that occurs in all cellulosic materials after immersion in water. The purpose of smoothing is to avoid deformations and restore, as far as possible, their original flatness and size. The best natural drying method after immersion is airing at room temperature and not too quickly, to avoid deformations. Documents are placed between two flexible and permeable covers on which gentle pressure can be exerted to complete the drying process and help to smooth them out (sections 6.3.12-6.3.12.2, pp.92-94.
If a document is in such a fragile state that despite the consolidation treatment is still risky to handle it it should be laminated by applying to one or both sides a reinforcing sheet that will lend it greater body and functional strength. This operation can be performed manually or by special machines with heat and pressure controls. Lamination is a curative method and should not be used on a large scale or indiscriminately. Lamination must be preceded by the appropriate curative measures, especially deacidification (sections 6.3.13-6.3.13-2, pp.94-97),
Other protective methods are applied to the restoration of bindings and the mounting or special protection of loose leaves or documents. For bindings of historical and/or artistic value the applicable criteria, as for all reintegration, are aimed at preserving the item in its integrity. When replacements are made the materials and techniques should avoid falsification and, while respecting the harmony of the original and reconstructing the missing parts, ensure that the old is clearly distinguishable from the new.
Binding entails dismantling and reassembling the entire volume if the leaves need treatment or if the binding has become weak. A careful record of the order and arrangement of each book is indispensable so as to avoid mistakes when rebinding (section 6.3.14.1, p.97).
Loose documents should be protected, especially for the purpose of display, by being specially mounted in a passe-partout folder to preserve them. The materials used, like that used in other treatments (e.g. binding), must possess certain innocuous properties (e.g. chemical neutrality, absence of particles subject to oxidation and low or zero hygroscopicity). A transparent and impermeable sheet placed between the folder and document eliminates external risks.
Another method is encapsulation, a system of preventive covering that consists in putting the document, without any adhesive, inside a flat, transparent and hermetically sealed sleeve and prevents or guards against the action of external agents. As with lamination, before encapsulating the document any agent that can cause foreseeable damage must be eliminated (sections 6.3.15.1-1-6.3.15.3, pp.100-103).