Cover Image
close this book Study on mass conservation techniques for treatment of library and archives material
View the document Preface
View the document 1. Introduction
View the document 2. Damage to library material and its causes
View the document 3. The situation in the libraries
Open this folder and view contents 4. Methods of conservation
Open this folder and view contents 5. Methods of restoration
View the document 6. Conclusive remarks
View the document Bibliography

2. Damage to library material and its causes

In order to be able to ascertain the various different kinds of damage to library materials and to be able to carry out suitable restoration work, a system to classifying the damage along with their causes was necessary. In the following pages all types of damage which actually occur in practice have been classified.

I. Mechanical damage

Under this heading We class all the kinds of damage which manifest themselves "physically". This kind of damage is characteristically found restricted to a particular area and slight damage of the "grey zone" type is uncommon here minis kind of detonate always occurs when the destructive forces put too great a strain on the inherent strength of the material constitution. Causes of mechanical damage can be due to:

a) the way the book is made

b) improper use of the book

c) violent influences from outside

For example, if a book falls from the book trolley during transportation, this could cause the book-cover from being torn from the book block. Very frequent turning of the books pages can easily lead to damage.

II. Biological damage

This is the collective name for all kinds of damage caused by various different living organisms. Biological damage differs in the way it occurs and in the effects from the attack.

Biological damage is caused by an attack of a) micro-organisms Bacteria: cause mildew marks restricted to certain patches (depending on the pathogen, changes in colour may also be registered) along with the enzymatic decomposition of the material substance.

Moulds: are, in practice, the most common causes of damage (up until now over 300 different species have been proved to exist on books and paper. The damage differs in colour over large areas on the most diverse kinds of materials - the would causes differing degrees of enzymatic decomposition , which has the character of chemical damage.

Micro-organisms are omnipresent on earth. Particularly the permanent parts of them, the spores, can be detected nearly everywhere, therefore logically also on library material. If favourable conditions such insufficient temperature, humidity and a culture medium coincide, then a development and propagation of the microbes along with an on-going decomposition of the culture medium begins, the medium being in our case containing cellulose. Apart from in the event of a catastrophe such as flooding, water damage from extinguishers after a fire or a leaking or burst water or heating pipe, a sufficient amount of water can be present through unfavorable temperatures and humidity in stockrooms. As paper is to hygroscopic material, it is possible to detect sufficient water to germinate spores (even with adherence to recommended climatic conditions). Microbes are capable, in an extreme case, of breaking dorm the cellulose to glucose during one life cycle. These chemical changes lead to serious types of damage with irreversible changes in the material.

b) Insects

According to biological species they cause typical, different-shaped bite-marks belonging to mechanical damage. Virtually all materials of paper or book structure are open to insect attacks .

Insecticidal pests are able to adapt themselves quickly to changes in their environment. This characteristic accounts for them being so widespread and for their infestations being constantly in new surroundings. Insecticidal pests find a more favourable environment in closed rooms inhabited by humans than in the natural world. As they are "parasites of civilization", they find protection from their natural enemies, more favourable climatic conditions and better basic food supply. The incidence of pests in collections and stockrooms depends both on different climatic and geographic conditions (subtropical regions offer a more favourable environment) and on actual ecological conditions. The structural state of the building, the microclimate, the culture substratum, the lighting conditions, the state of order and cleanliness all have a considerable influence on Whether development and multiplication can occur , in the from of active migration (by penetration of insecticidal pests from outside, for example, during times of swarming, or in the form of passive migration through infected books or packaging The holometabolic insects are the most important group of all the book pests (whose development leads from egg to larvae and pupa to fully-grown insect or imago). Damage (such as shavings, bore-holes etc.) are not always sufficient evidence to identify the kind of pest. The discovery of new bore-holes or areas which have been eaten away, larva shells, pupa skins or cocoons should be good enough reasons to take action.

c) rodents

Rats and mice are typical examples of harmful rodents which do mechanical damage particularly to the exterior parts of library material which can be recognized through traces of gnaw and bitemarks. Structural deficiencies in cellar and roof stockrooms can be held responsible for their penetration. If materials are stored in stockrooms which are seldom, frequented or hardly checked, then it is fairly likely that damage will occur by rodents.

III. Chemical damage

This group includes all types of damage which in the widest sense is caused by chemical reactions and whose causes are

a) Reactions which are long-term processes of a natural character,

b) Reactions which are accelerated by components prone to reaction,

c) Reactions caused by substances which penetrate from outside.

Irreversible changes to the material structure are common to all kinds of chemical damage. We can only name clear manifestations of this in very few cases. The different categories overlap one another and accumulate.

The restorer comes across chemical damage belonging to this category most often on original material. The treatment of this sort of damage demands a great deal of skill and ability on his part.

The ageing process of caper is the result of on-going chemical processes. How fast this actually happens depends on different factors, although An exhaustive scientific account is still not possible with our present level of knowledge. A list of all factors involved which are already known to us, and an exact understanding of the way they react together is necessary in order to explain the process of ageing. Cellulose, being the basic element, forms the main element in the plant cell walls and is the most commonly occurring carbohydrate in the world of nature.

When pure cellulose is heated in correspondence with the values from the calculated molecular weight, an elementary analysis yields the formular (C6H10O5).

Cellulose is a colourless substance which is not soluble in water or in most other organic solvents.

Large amounts of glucose residue are connected by b-glucosidic I.4 oxygen bonds of long chains. In the macro-molecules the group (C6H10O5) repeats itself many times. The n after the bracket indicates the amount of links in the chain.

The degree of polymerization (polymerization: the joining together of similar smaller molecules to form macro-molecules and the size of the molecule is identical. The average degree of polimerisation (ALP) shows how many links C6H10O5 there are in the cellulose molecule.

The production of cellulose fibres as the basic material for making paper was, for centuries, predominantly a physical process. Flax, linen, ramie, cotton and other plant fibres consist of more or less pure cellulose. Flax fibres contain between 0.5 - 2.0% lignin according to provenance. The cellulose fibres are won either directly from the plants or indirectly via textile fabric through mechanical separation. need be, the cellulose fibres then underwent alkaline treatment, but remained to a large extent in its natural form. By the end of the 19th century sweeping changes had taken place. The acquisition of cellulose fibre from wood and the process of chemical splitting altered the raw material base used in paper production, which also comprised considerable technical changes in comparison to the usual procedure of production up to that time.

When paper ages, the polysaccharidic elements of the fibre walls undergo negative changes both mechanically and optically. A breakdown of the polyeaccharide (cellulose and hemicellulose) groups, together with an increase in the carbonyl and hydroxyl groups causes a decrease in the folding endurance. Research relating to this showed that when new paper is folded, the bonds between the fibres loosened, while the folding of old paper lead to breaks in the fibres.

The carbonyl groups, being the most reactive, have, along with the results of the oxydative changes, an effect on the reactivity of neighbouring groups (for example, the breakdown of the Bglucosidic bonds) and are decisively important in the format ion of chromophores (responsible for yellowing). The breakdown of cellulose by acids leads, apart from an attack by the H-ions on the b-glucosidic bonds, also to a rupture in the periodically established flaws which are arranged in levels and restrict defined elements of fibre.

In this way, ruptures occur &cross the fibre wall, the ALP sinks and the polymer-homologous hydrocellulose comes into being. The characteristics of hydrocellulose are dependent on the eight of the molecule and, in fact, as the breakdown goes on, the alkaline solubility and reactivity increase but the strength decreases. The ALP quantity to be measured and the alkaline solubility give a great deal of information on the state and strength of the cellulose. They are a way of measuring the damage to the fibres. The acid-hydrolytic breakdown can be expected in all paper 'which has been made in an acid medium. The oxydation of the cellulose into oxycelluloseoccurs particularly easily during the bleaching of the cellulose if this takes place in an acid medium or at too high a temperature. Oxycellulose, whose fibres are superficially attacked, possesses a reduced amount of strength through the formation of carboxyl groups and the oxidation of secondary hydroxyl groups into dialdehyde cellulose. Evidence of this is usually tested using Fehling's solution on the cellulose, whereby a higher reading denotes a worse quality

A further considerable fact affecting the ageing of cellulose is the refining of the half stuff.

During refining the inner structure of the fibre wall is loosened resulting in it splitting up into segmented elements even more, through which water can more easily penetrate, therefore making the fibres more flexible and malleable.

Furthermore, the surface of the fibres become fibrillated, which greatly enlarges the bondable surface and improves the bonds between the fibres. The breakdown of the strength bearing polyeaccharide is accelerated by this loosening of the structure and the polymerization level of the breakdown products decreases.

The greater initial strength of the paper aimed at in the first milling or refining is no guarentee for its durability. The substances responsible for the yellowing in bleached cellulose are low molecular polysaccharide by-products with a high concentration of carbonyl and carboxyl. The format ion of chromophore groups is very much assisted by the mechanical effects of the milling.

The breakdown of cellulose and hemicellulose by microbial enzymes produces a multicomponent system. Many cellulotically active micro-organisms synthesize cellulase, which converts the substratum of the paper into glucose. Three combined elements in an enzyme complex are necessary for this.

CI-cellulase, Cx-cellulase and b-glucosidase have been detected in trichoderma viride myrothecium verucaria culture mediums, in different aspergills and in other fungae and bacteria. Only in unison are these three enzymes capable of breaking down cellulose to glucose.

CI attacks native cellulose, leading to a loosening of the bonds, which through hydration of the substratum contributes to further water absorption and the densely-joined chains are driven apart. Cx-cellulose works in a hydrolytic way and attacks amorphous cellulose and cellulose derivatives.

b-glucosidasel acts on cellobiose (a structural element of cellulose) and on other glucose b-dimers.

If filter-paper is used as a culture substratum, the cellulase of 6 aspergillus species will cause a decomposition of 55-88% to take place. Ten kinds of wood-fungi caused a decomposition of between 3-91%, four sorts of penicillium up to 61% decomposition, four types of trichoderma up to 53% decomposition. Leaving the microbes enzymatic system of decomposition, the fact that the organic acids are capable of synthesizing must also certainly have a destructive effect. he aspergillus species are used for example on an industrial scale in the production of citric and gluconic acid.

These chemical processes of decomposition must be seen al together in connection witch the external factors of long- term storage. Temperature, humidity, light and air pollution have a considerable influence on the speed of ageing in cellulose products. Temperature and humidity, in their dependence on nature, are primary sources of influence on hygroscopic materials such as paper, leather and parchment. It is plausible that chemical processes are more likely-to increase under higher temperatures and humidity. 25°C and 32°C seem to be critical temperatures at which the ageing of paper speeds up progressively. At higher temperatures the water molecules in the paper are present in an isolated form and are more active, whereas at low temperatures the H2O molecules remain in concentrations which are inert to reaction. Humidity is determined by the amount of steam in the air. The relative humidity is the ratio of absolute humidity to the prevailing temperature possible at saturation point - that is maximum humidity. This information can be gained by reading the hygrometer in per cent.

The degree of saturation can be ascertained by the data on the table - for example


15°C 12.8 g/m3 air

20°C 17.3 g/m3 air

25°C 23.0 g/m3 air.

The absolute air humidity rises with the constant relative air humidity when the temperature rises by nearly twice as much again from 15°C to 25°C, that is, from 7.68 g/m3 to 13.S g/m3. These ratios are of particular interest in regard to the micro-climate in the stockrooms or exhibition rooms, and they should be taken into consideration when decisions on controlling air humidity are made. Particularly hydroscopic material such as parchment reacts very vigorously to these differences and c-en in extreme cases cause great damage. The ability to absorb water from the ambient air differs considerably both within the material group (for example paper) as well as between the different material groups themselves. The negative influence of air pollution in the form of sulphur dioxide, nitric oxide and chlorides on the lifespan of objects is particularly well illustrated by the weathering of stone monuments. The effect of aggressive atmospheric elements on books and paper has an intensified effect on the process of decomposition. The destructive effect of ultraviolet rays on the molecular chains in paper is particularly serious in the wave-lengths between 300 - 500 nanometers. The greatest proportion of these ultraviolet rays are found in sun and daylight. The photochemical reactions can on the one hand lead to paper-yellowing, on the other hand to the bleaching out of inks and pigments. the energy which accumulates due to the ultraviolet rays leads in differing degrees to the breakdown of chemical bonds in the material which leads to the occurrence of free radicals. Their reaction to oxygen starts off a chain reaction, which in the end can lead to the total destruction of the paper (photolysis).

It should also be mentioned that the diffusion of harmful substances through direct contact of the paper with unsuitable materials is also possible. Pass-partout materials, glues, protective foils etc. involves the risk of spreading harmful substances. It may also be possible that products such as softening agents or also acidic by-products of the contact materials can cause damage.

Internal and external causes of paper-ageing, or to be more general, of the ageing of historical materials, can, in the job of the restorer mostly be registered as conclusive phenomena, which, apart from the physical and chemical changes in the material, also lead to aesthetic changes in the object.