The Centre de Recherches sur la Conservation des
Documents Graphiques (CRCDG) founded in 1963 is a joint unit of the Centre National de la Recherche
Scientifique/ Ministere de I'Education Nationale et de la
Culture/Museum National d'Histoire Naturelle. Its function is to conduct research to ensure the preservation of the cultural heritage which consists of books, archives, drawings and photographs. Recently its field of investigation has been extended to archaeological leathers, in this laboratory more than twenty researchers, engineers and technicians endeavour to develop processes enabling documents to be preserved in their original state for as long as possible. They also accomplish the important task of identification so as to inform conservators of the exact nature of the materials to be restored and provide historians with information on the animal origin of leathers unearthed from excavation sites.
The research laboratory is divided into several sections, three o! which specialise in the conservation of the following materials: paper, leather, parchment,and photographic documents. A microbiology section has the objective of combatting destructive insects and microorganisms. In !he event of contamination, samples are taken, and after species identification, strict instructions are given to curators regarding disinfection and prevention. In addition, research has been carried out on the efficacy ol new molecules whose bactericidal and fungicidal powers make them suitable for use in the field of conservation. The section's activities involve not only all graphic documents but objects conserved in museums.
The CRCDG is also a consultant to those responsible for collections, especially in emergencies such as flooding; in addition, it has also a teaching function both at the higher education level and in continuing training for curators and conservators. Lastly, it is in contact with many of its foreign colleagues through various international bodies, in particular the Conservation Committee of the international Council of Museum. The willingness to cooperate is visible in the part which the centre plays within the European Economic Community, in the STEP programme (Science and Technology for Environmental
Protection), one aspect of which is devoted to safeguarding trie European cultural heritage.
As paper is the essential constituent o! graphic documents, we have chosen to present some recent research carried out on the analysis, preservation and restoration of this material. To stop the damage caused by acidification over time and to develop protective techniques, the decomposition of different qualities of paper exposed to pollution was studied.
Aiming at long-term conservation, we have taken an interested in the stability of the optical brighteners added to paper during manufacturing to increase its whiteness and in the choice of a printing ink compatible with archival paper. Finally to improve some restoration techniques it seemed necessary to find a way of fixing unstable inks o! contemporary manuscripts before treating them.
Prior to 1650, paper was produced from white linen or
Hemp rags washed in 'hard water 1 containing alkaline carbonates (magnesium and calcium), bleached with wood ash and left to dry in the air. Most of these papers have stood the test of time and are in an excellent state of preservation today. Unfortunately, this manufacturing process changed. Around 1650, alum (potassium and aluminium sulphate) was added to pulp to harden the animal glue size but had the adverse effect of increasing acid content in particular through the formation of sulphuric acid.
Since the end of the eighteenth century, the ever increasing demand for paper required the use not only of white linen or hemp rags, but also coloured rags from
(a) H
3
CO Mg O COOCH
3
+ 2H
2
O ~> Mg(OH)
2
+ 2CH
2
OH
(b) H
2
O + CO
2
-->H
2
C0
3
(c) Mg(OH)
2
+ H
2
CO
3
-->MgCO
3
+ 2H
2
O
(d) MgCO
3
->MgO + CO
2
(e) Mg(OH)
2
+ H
2
SO
4
-> MgSO
4
+ 2H
2
O
(f) MgCO
3
+ H
2
SO
4
--> MgSO
4
+ H
2
CO
3
(g) MgO + H
2
SO
4
-
•> MgSO
4
+ H
2
O which the colour had been removed to some extent.
Many products were tried as bleaching agents until the discovery of chlorine in 1774 revolutionised paper bleaching techniques. Unfortunately, chlorine, in contact with moisture, produces strong acids which accelerate the destruction of paper. By the middle of the nineteenth century, great progress was made in paper manufacturing.Wood pulp gradually replaced rags. When insufficiently treated, wood pulp contains non-cellulose products such as lignin which, when in contact with light, heat and moisture, also produce acids.
However, the main cause of acidity in the paper from this period is due to the presence o! rosin which was used as a sizing agent. When combined with alum it forms an aluminium resinate which precipitates on the fibres and gives the paper good water resistance and imparts good writing quality. It has been proved, however, that this sizing process releases a substantial amount of sulphuric acid.
From this brief historical outline we can see why the papers of the eighteenth, nineteenth, and the beginning of this century have become brittle and often very coloured.

Effect of pollution on paper
Although the products used in the manufacture of paper are the source of its acidity, the damaging effects of external factors such as atmospheric pollution should not be neglected. Corrosive gases such as SO
2
, and NO
2 are absorbed by paper in quantities corresponding to its

porosity and on exposure to atmospheric humidity are converted into sulphuric and nitric acids. It is not only vital to neutralise She acidity of the celluiosic materials but also to prevent further acid deterioration by giving an alkaline reserve.
The awareness of this phenomenoa by chemists is not new, since it is found in the writings of Faraday,
Calvert and Letbely as early as the 1850's. They noticed the adverse effects of acidity on books and attributed the atmospheric pollution to the combustion gases of lamps.
Nevertheless, it was not until the early part of this century that neutralising methods were first developed.
Various compounds have been used for this purpose such as sails and oxides o! alkaline earth (Ba, Ca, Mg), and alkaline metals (Na, K, Li), borates, phosphates, aromatic and aliphatic amines, and alkaline salts of fatty acids. They can be used in aqueous or alcohol solutions and also in gaseous form.
Many so called 'deacidification' methods have been developed throughout the wood; soaking in alcoholic or aqueous solutions is limited to the treatment of small numbers of loose sheets or unbound documents.
Considering the large quantities of books and periodicals requiring deacidification, it was necessary to develop mass treatment methods to meet some requirements; the first one being a good penetration of the products to the core of the documents piled up in the treatment autoclave. For this , gases or pressurised solutions were chosen. The compatibility of alkaline salls with the other constituent of the books (binding, glue, inks) has to be taken into consideration. Lastly, to save time and money, preference was given to treatments requiring a minimum of preliminaries. Very tittle research has been done on the phenomenon of the reacidification of treated paper over time and the mechanisms involved.
Thus we decided to include these two problems in a
STEP research programme. This one was begun in July
1991 and will last three years. The goal is to determine the best storage conditions and the choice o! deacidification treatment. The sludy covers a large number of papers of different qualities, including most of those preserved in archives and libraries. Modern pure rag, 100% bleached chemical pulp and mechanical pulp papers have been selected as well as old papers of varying age and origins.
All these materials were exposed to pollutant gases for two weeks (13 ppm SO
2
and 25 ppm NO
2
at 23
°C and 50%
RH). They were artificially aged for twelve days in an oven at 90
°C and 50% RH.
A large number of chemical, spectrornetric, mechanical and microscopic tests were carried out on the untreated, polluted, deacidified and, deacidified then polluted, papers.
As regards the deacidification techniques, for preference we chose mass methods, which are the only ones permitting the rapid treatment of very large collections presently in peril. Among the ten or so existing techniques, we decided to study the four which seemed !o us to be the most efficient.
Deacidification with magnesium methoxtde under pressure (technique developed by Weit o)
In 1977, Richard Smith designed a prototype in which he used magnesium methoxide under pressure. Two years later, Weit'o installed a pilot station in the Public Archives of Ottawa which has been operational since 1981. In this method of deacidification, methyl magnesium carbonate deposited on the fibres reacts with moisture in the atmosphere to form a mixture of salts (hydroxides (a), carbonate (b) and oxides (c)) which neutralise the acids present in the paper and give it an alkaline reserve (e) (l)
The documents are first dehydrated to ensure good penetration of the compound which otherwise would precipitate and leave on the surface an unsightly deposit of MgO. This process seemed very promising because it is easy to use and efficient. We improved it by replacing the rnethanol with ethanol whose compatibility with the writing was better and we calculated the concentration of active products and the exposure times. The results of this study were used in France by the National Library as a prototype at its restoration centre at Sable sur Sarthe in 1984. This station in service since 1987, treats about
100 books a day with good results.
Deacidification with zincdiethyl (technique developed by Akzo) 2
In 1970, J Williams and G Kelly presented a deacidification method using the gas zinc diethyl (ZDE) it reacts with the acids in the paper (sulphuric and acetic acids) and converts thern into neutral non-volatile sulphates (a) and acetates (b) and releasing ethane, an inflammable, asphyxiating gas.
It also reacts with the water contained in paper giving off ethane antizincoxide (c) which is immedately deposited on the fibres giving the paper an alkaline reserve of up to
1.5% ZnO.
Nevertheless, in its liquid form it is pyrophoric. As a result, the treatment must be done at a low pressure and in a nitrogen flow. The operation is carried out in a large capacity autoclave in a vacuum without preselection of the documents but dehydrating them before treatment.
5000 books can be treated in a single operation.
Deacidification with magnesium butoxytriglycolate
(MG3) (technique developed by Lithco-FMC) 3
This method is similar to the one used in France. The active product is an aikoxylated compound, solubilised in chloroftuorocarbon. which has the dual effect of neutralising and reinforcing the paper. Prior dehydration of the documents is necessary; 150 volumes are treated by a cycle of four to six hours.

deacidification with amine ethylenes
(technique .developed by Book Preservation
Association BPA} 4
This is a gaseous process presently in the experimental stage, it is realised in an autoclave in a vacuum by combining the action of gaseous ammonia (NH
3
) and ethylene oxide (CH
2
-0-CH
2
). The products formed are a mixture of mono-, di- and tri-ethanolamine
(NH
2
CH
2
CH
2
OH; NH(CH
2
CH
2
OH(CH
2
CH
2
OH)
2
which are basic amines capable of neutralising the acids contained in the papers and constituting an alkaline reserve. No preselection or pretreatment of the documents has to be done.This method is rapid (twentyfour hours), inexpensive and easy. The products deposited on the fibres are non toxic. However, there remains the problem of ethylene oxide neutralisation upon removal from the autoclave. Data on the efficacy of the technique is unavailable.
The first part of the STEP programme therefore consisted in defining the experimental conditions as wet! as the characteristics of all the papers used in the experiments. We now begin the study of the mechanisms involved during the degradation of the different papers exposed to pollution. The last part of this work will concentrate on a behavioural comparison between the papers deacidified by the four methods described above.
As mentioned earlier, some papers sized with rosin in an acid environment have greatly deteriorated. Research has been carried out for many years to determine the best characteristics for a permanent paper in order to guarantee the life expectancy of valuable documents.
An ISO 5 standard is being developed to qualify conditions of permanence, it has been found that this kind of paper should be 100% bleached chemical wood pulp free of lignin, sized in a neutral medium and filled with an equivalent of 2% calcium carbonate. Its pH should be around 8. The possibility of optical brighteners being present is tolerated.
Optical brighteners are substances that neutralise the slight yellow colouration of paper thus making it whiter.
While in the past, blue natural pigments were used, nowadays fluorescent substances derived from stilbene are employed. They absorb ultraviolet radiation re-emitting visible blue light, so that paper has a whiter appearance.
As these substances are sensitive to heat and light they were studied for their long-term effect on cellulose. The optical, mechanical and chemical properties of different papers with brighteners were analysed and the results compared to those obtained from identical papers without brighteners. The study was carried out on several qualities of paper supplied by different manufacturers. All were made from bleached chemical pulps, sized in a neutral medium and filled with calcium carbonate except for
100% cotton linters paper (with no size or filler) which was included to study the behaviour of pure cellulose.
Measurements of the optical, mechanical and chemical parameters were carried out before and after two types of artificial ageing: wet heat (80 °C. 65% RH for twenty four days) and light (150 hours on each side of the paper under a xenon lamp at 30 °C, 50% RH). There is no doubt that optical brighteners improve paper brightness. During ageing (especially with light) brightened papers lose more whiteness than non-brightened ones but are still whiter.
Optical brighteners do not significantly modify the mechanical and chemical behaviour during ageing of the treated papers (the pH of brightened papers is always slightly higher than that of non-brightened ones).
Conversely, papers made from rag pulp deteriorated
"much more when containing optical brighteners.
The compatibility of modern printing inks with permanent paper, and the stability of documents printed with these materials was studied with the intention of preserving documents of artistic or historic value.
Basic black printing ink, used in offset printing which is the most widely used process in France, was chosen for the study. Samples were selected from among the principal ink manufacturers on the French market(Basf,
Brancher, Grant, Lorileux, Sicpa, Sun Chemical).
For each sample, several preliminary tests were performed to characterise the inks and to determine their compatibility with permanent paper. Measurements of viscosity, rigidity, tack 6 , and printability make it possible to anticipate any risks of picking (if tack is too high), inkfly 7
(if viscosity is too low), and blotting 8 (ii drying is too long).
All these preliminary tests showed that the fifteen selected inks were compatible with permanent paper.
Next, real size machine prints were made with each ink on permanent paper at l'Ecole de Papeterie de Grenoble,
All existing types of offset printing were represented: flatness, half-tones, text and control bars for each sample.
One hundred A4 format copies were printed and their stability was examined before and alter two types of artificial ageing: wet heat (twenty-one days in an oven at
90
°C, 60% RH) and light (300 hours under a xenon lamp at 30
°C, 50 % RH).
............
The following tests were used: on a black disc, recording of trichromatic values; on half tone plates, colour differences, measurement of black optical density, reflectance and contrast; on the flatness, measurement of pH levels of cold aqueous extract.
At this point in the research we can conclude that after wet heat or light ageing neither the colour nor the density of the fifteen inks showed significant modification.
Furthermore, the pH levels of printed papers remained unchanged (close to 9), which indicates a large alkaline reserve. Thus the black ink offset prints on permanent paper retain their visual and chemical qualities before and after artificial ageing. The bonding capa-:ny seems satisfactory.
Simultaneously, in order so explore the full range of oifsel Sour-colour printing (cyan, magenta, yellow and black) we are studying the behaviour of coloured ink samples using the same tests. In fact, although there are some very fast blue inks, the pigments used for yellows and magentas are less resistant to light.

Most of the numerous methods of paper restoration in use throughout the world for the past several decades, require in most cases immersion of the document ir aqueous or organic solutions. For example, in the leal casting technique, paper pulp suspended in water and deposited in the gaps by means of rapid suction; the document must remain immersed in the water for several minutes.
in addition, the deacidification methods used most often in the workshops for the treatment of rare or targe documents or even small quantities of sheets, require the use of aqueous or alcohol solutions. Other restoration processes, which we cannot describe here (sizing, bleaching, etc) also call for the use of different solvents.
Inks used in ancient manuscripts (carbon or ferrogallic inks) are generally insoluble, but the same does not apply to inks used in some contemporary manuscripts (fountain pen or felt-tip pen inks, etc). Therefore, the problem of fixing them before treatment had to be resolved.
For this, substances had to be selected which were suitable yet considered harmless with regard to the paper. Few articles treat this particular problem. Recently,
K Bredereck stressed the importance of the ionic nature of the colourants found in inks. The conclusions of this study show that different chemicals (condensates of dicyandiamide and formaldehyde; polyethylene imine and di- or polyhalides; salts of stearyl dimethylbenzyl ammonium) give good results in fixing.
We employed Sandoz products (Dermafix S, Indosol
E50, Tergolan GS, Sandofix WE), generally used for fixing dyes. A preliminary study was carried out on contemporary archive documents comprising different types of ink soluble in water or organic solvents. The concentrations, immersion times and drying methods giving the best fixing were determined for each product.
We also examined the effect of deacidification, using magnesium bicarbonate, on the inks thus treated, as some of these fixing agents are acidic.
By simple visual observation four fixing agentswere selected for water solute inks: X321, lndosole 50, Tanigan
LD and Sandofix WE (Fig. 1'). The first three are effective only on blue inks and Sandofix WE 9 on black, blue, red and green inks. For the inks soluble in organic solvents, in order to avoid water/solvent mixture, the four fixing agents were used in powder form and dissolved in various organic solvents. The best results were obtained by immersing the papers for one minute in a solution of
Sandofix WE in methyl alcohol. Although some inks were very well fixed, others were not fixed at all (in particular
Reynolds and Unix 2001 ball points).
Given these brief results we decided to further study the stability of the inks treated with Sandofix WE and the harmlessness of this fixing agent with regard to paper.
The work presented here concerns only research on water soluble inks, as the Sandofix WE had not given total satisfaction for inks soluble in organic solvents.
Stability of inks treated with Sandofix WE
Fountain pen inks in four colours (black, blue, red, green) marketed by Parker, Pelikan and Waterman were selected for this study. Lines were drawn with these different inks using a drawing pen on permanent paper.
Line profiles 10 : For each ink the line profiles were executed and compared with one another. The lines were recorded on video and analysed numerically
(Graftex-Optilab software). The samples were divided into three parts. The first one serving as a reference was not treated, the second was immersed for one minute in water and the third was soaked for one minute in a solution of Sandofix WE then rinsed thoroughly with water. From this analysis we learned the variation in ink density (height of peaks) and the migration during treatment
(width of peaks and base lines).
In general, the optical density of inks immersed in water containing Sandofix was not modified (except for green Waterman ink); that of the inks immersed and not fixed decreased considerably (Waterman black and blue,
Pelikan blue, all the green inks and almost all the red inks).
After fixing with Sandofix no migration appeared, though for the lines not fixed we noticed that some peaks were enlarged and that the base line was modified in many cases. This proves thai the ink spread on the paper
(Fig.2) 2).
Colorimetric analysis:This was done using a nanometrtcs microspectrophotometer. The trichromatic coordinates were calculated using the CIELAB" formula.
With the exception of Parker blue ink, we observed a great variation of colour for the inks immersed in water (especially for the Waterman inks). This is perfectly normal considering the high solubility of these
Fig. 1 Behaviour in water of fixed manuscript inks
Fig. 2 Control of the efficacy of Sandofix and line profies of the samples inks. For

the inks fixed with Sandofix, the variation in colours is slight (except for the Waterman inks).
Harmlessness of Sandofix WE with regard to celluiose
The samples were soaked for one minute in a 10% aqueous solution of Sandofix WE then rinsed. Half of them were then deacidified by immersing in a solution of magnesium bicarbonate for five minutes; the other part was not deacidified. Physico-chemical analysis was carried out on these papers before and after ageing( .7, days a! 90 °C, 60% RH).
/
The results of this research have proven that Sandofix
WE fixes all the water soluble inks tested with no noticeable discolouration. For inks soluble in organic solvents and stamp pad ink the study is presently continuing in order to find a better solution.
This report is only a brief summary of the principal problems relating to the preservation of written or printed documents which the CRCDG has tried to solve. Other important research such as a study on the disinfection of documents is slill at a preliminary stage, but is essential to progress in the field. It involves finding a substitute for ethylene oxide which has been used since the 1960'sto eliminate microorganisms found on the paper. However its use is prohibited in some countries. We are now examining different treatments borrowed from the field of physics such as gamma rays, electron beams, microwaves, radio-frequencies, which are already used on a small scale by foreign colleagues. Our aim is to be able to give a scientific opinion on their efficacy and to ensure their harmlessness with regards to the documents.
References
1. Weit'o Associates INc, Matteson. Ill 60 443, USA.
2. Akzo Chemicals Inc, Chicago, USA.
3. FMC Corporation, Bessemer City, USA.
4. BPA Book Preservation Associates, New Jersey,
USA.
5. ISO standard 46/CN 10N.
6. Cohesive force which opposes the separation into two parts of a film of ink.
7. Complex phenomenon of partial dispersion of the ink, linked with the film forming structure of the ink, the speed of the rollers and external conditions.
8. Smears due to too long a drying time.
9. Sandofix W E is a polymer of dicyandiamide, formaldehyde ammonium chloride.
10. The profile of the line is a curve of luminosity of a defined vector. In the present case this is a segment of fifteen millimetres, perpendicular to the lines drawn.
11. CIELAB standard of the International!
Lighting Committee
Aitherr, E, Optical brighteners, American Dyestuff
Reporter, 29, (1965) pp 38-48.
Arnoult, J M, Mass deacidification in France, Restaurator,
8,2-3, (1987) pp 100-105.
Blank, M G, O zakreplenil chernil nykh tekstov, 0 sokhranenit bumagl, proisvedenil pechatt i rukoplsei, (1963).
Brands, A, La deacidification de masse du papier - Etude comparative des precedes existanis, Bibliotheque
Nationals Pro Libris Paris (1992) p 88.
Bredereck, K and Siller-Grabenstein, A, Die Moglichkeiten der Festigung von Fasbsioffen und Tinten als
Voraussetzung fuerdie REstaurierungsmassnahmen in Archiven und Bibliothken, internationalen
Graphischen Restauratorentag, Berlin (1987) p 3,
Bredereck, K, Bluher, A and Siller-Grabenstein, A,
Untersuchungen zur Fixierung von Schreibstoffen auf modernen papieren als Voraussetzung fur
Restaurierungs und Konserveirungsmassnahmen in
Archiven, Das Papier, 44, 4 (1990) pp 137-146.
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Flieder, F, Leclerc, F and Arnoult, J M, La deacidification de masse des papiers en France, Technologies
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(1989), pp 68-80.
Kunz, W, Whitening agents. Significance and purpose,
Deutsche Papierwirtschaft, 3/4 (1989) pp T42-T46.
Leach, R H, The printing Ink manual, 4th edition (1988)
Leroy, M and Flieder, F, Le colmatage mecanique des iacunes des manuscrits anciens et contemporains,
Actes des journees de L'ARSAG Paris (1991).
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202.
Muller, F, Unterbtrker, HandJostama, J, Azurantsoptiques: nouvelles tendances dans I'indusfrie papetiere et leurs consequences, Papier, Carton et Cellulose,
(1987) pp 85-92.
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Workshop of STEP project (1992) (report not published).
Reinhardt, 8 and Arneberg, U. Einfluss von hilfsmitleln auf die Papiervergilbung durch licht und Temperatur,
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223-230.
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Local Organising Committee:
J B J Hofmeijer P
Hoogendijk P
Kaper J Lodewijks
W B J Polman
K W Stuyterman van Loo
R J Willink
ISBN: 1 871656184