A Bibliographical Survey of Mass DeacidificationMethods

by ANNE LIENARDY

1. INTRODUCTION

2. DESCRIPTION OF THE METHODS NOT TESTED2.1 Battelle Institute method2.2 Ammonia2.3 Morpholine2.4 Interleaf2.5 German method2.6 Graft copolymerization2.7 Paper splitting

3. COMPARISON OF TESTED METHODS3.1 General introduction3.2 Treatments3.3 Results3.4 Output3.5 Costs3.6 Staffing3.7 Safety3.8 Independent testing3.9 Advantages3.10 Disadvantages3.11 Suggested improvements

4. CONCLUSIONS SUMMARIES REFERENCES

1. INTRODUCTIONAs in most conservation institutions, techniques for mass deacidification are being studied in the Institut royal du Patrimoine artistique, Brussels. We have treated samples of the same paper by different methods. Chemical tests for evaluating the results are underway and will be published.This article summaries the bibliographical study undertaken as the first stage of our work. The first part describes the methods we did not test together with the reasons for our decisions. The second part describes in detail the characteristics of the methods we did test, together with the treatments themselves, possible consequences for the books, advantages and disadvantages, as well as possible improvements that can or should be made.We reviewed 15 so-called mass treatment methods:

This article was written in November 1990.

Ammonia FMC method*Archival Aids* German methodBook Preservation Associates* Battelle Institute methodBookkeeper* Vienna method*Interleaf MorpholineDiethyl zinc* Paper splittingGraft copolymerization Parylene* Wei T'o** indicates a method actually tested

These methods are considered mass treatments because: they allow the simultaneous treatment of several dozen books, the bindings do not need to be removed for treatment or the simplicity of the method allows rapid manual treatment of a large number of books.The methods actually in use include that based on carbonated magnesium methoxide, working in the National Archives of Canada, and that based on carbonated magnesium methoxide ethoxide used in the Bibliotheque Nationale in France. The Osterreichische Nationalbibliotek uses a solution of calcium hydroxide and methylcellulose. In India ammonia still continues to be used. In the United States, at the Virginia Library, Richmond, deacidification was carried out using morpholine.Yet other systems are still in the experimental stage. In the United States three new systems are being developed. Book Preservation Associates is proposing a system based on ethylene oxide and ammonia. Preservation Technologies is suggesting, under the name of the Bookkeeper Process, a mass deacidification system using a dispersion of particles of magnesium oxide. The third system, that of the FMC group, involves impregnation with a magnesiumorganic compound. In Germany, at the Battelle Institute, the installation of a system using improvements on the technique used in France is being studied.Other techniques, more oriented towards consolidation of the paper, are also being developed. One being tested in the United Kingdom could also deacidify. The other, being studied in the United States, can only reinforce the paper.To make this clearer we could update the table (Table 1) presented on several occasions by Banik.1-3

For the methods we tested, information obtained from the literature was supplemented with information obtained from people using the techniques or from those promoting them. We have still not received an answer on the method promoted by Book Preservation Associates.

Table 1. Known methods of mass deacidification

2. METHODS NOT TESTEDOf the 15 methods listed earlier, seven were not tested. For three, it was because the results obtained are not permanent: ammonia, morpholine and cyclohexylamine carbonate. We don't consider paper splitting as a mass treatment since it is essential to remove the binding. The method at the Battelle Institute, Frankfurt, FRG is still being developed.We could not test two of the methods selected. The method being developed in the Niedersachsisches Staatsarchiv, Bückeburg, FRG is still under trial. According to Feindt,4 participation in a programme of independent evaluation was not anticipated before the beginning of 1991. At the British Library, the first stage of its programme on the use of acrylic resins for consolidating paper has been completed but testing of the method by others must wait until a pilot plant comes into service.5

2.1 Battelle Institute methodWork on developing this method began in 1989.6-9

The deacidifying agent is carbonated magnesium methoxide ethoxide (CMME) as in France.' The intention is to build a pilot plant that would try to improve some of the inadequacies found in the existing installations. These include the emission of chlorofluorocarbons (CFC), the length of treatment time, especially the drying stage, and the cost. The objective is to finish treatment in two hours. The planned pilot plant will have a capacity of 100 books per cycle and the output would be about 150,000 books per year. Tests were planned to begin in October 1990.This method could not be tested since it is only in the development stage.

2.2 AmmoniaThe technique using ammonia was developed by Kathpalia during the 1960s and, according to Cunha, is still being used in the Nehru Library, New Delhi, India.10- 14

The advantages of the method are low cost, ease of use and no alteration of inks. The disadvantages are nonpermanent treatment (the compound is volatile), changes to the paper and residual odour. The method was excluded by Flieder12 in 1975 after testing.We did not test the method, given its impermanence.

2.3 AlorphohneThis method was invented by Kusterer and Sproull in 1973 at the Barrow Laboratories then developed by Walker for use at the Virginia Library in 1977.10-12,14-16 The method has never gone further than installation of a pilot plant in the Virginia Library in 1977 and was apparently subsequently abandoned.10

The advantages of this method were cheap treatment with a disinfectant effect. The disadvantages were that selection (because of pigment vulnerability) was required, the material used was dangerous (toxic), a residual odour was left and there was inadequate neutralization.The method was not tested because of inadequate neutralization.

2.4 InterleafThis method was invented by Langwell during the 1960s and developed by Campbell.6,10-14,16,17 A new formula has been proposed by B. G. Robertson

Laboratories (1988 onwards) and Interleaf Inc. (in the United States) is the sole distributor.

The deacidifying agent is cyclohexylamine carbonate. The method has been used in several institutions in the United States, in the Public Records Office, London, UK and in the United Nations collections, Geneva, Switzerland.13

The advantages of the method are that it is cheap and simple, requiring no complicated infrastructure and no need for drying or dehydration, which is useful when neither aqueous nor nonaqueous deacidification is possible. The disadvantages are the use of a compound suspected of being harmful to health, the need for selection (both inks and coloured material), a permanent odour that can be reduced through use of sachets containing activated charcoal, nonpermanent deacidification and slow reaction in any case.The results of a physicochemical testing programme at the Chicago Paper Testing Laboratory were planned for March 1989.10 So far as we know, nothing has yet been made public.We did not test the method because the neutralization is inadequate.

2.5 German methodThe method is being developed by the Niedersachsisches Staatsarchiv in collaboration with the Paper Technology Institute, Munich, FRG.3,10,18

The deacidifying agent is magnesium bicarbonate. First, there is a pretreat-ment to fix the inks, followed by immersion deacidification. Consolidation using carboxymethylcellulose follows, then drying. A machine for treating large quantities of archive materials is planned so that 600 A3 size sheets could be treated in one hour.18

The method was not tested because it is still being developed.

2.6 Graft polymerizationA method developed by the British Library in collaboration with the University of Surrey,3,10,12,13,19-23

this method of consolidating paper is at an experimental stage for the British Library.Its advantages are: strengthening of fragile papers, treatment of both loose leaves and bound books together with possible deacidification. The disadvantages are the need for selection because of ink vulnerability and irreversibility.Independent testing has been carried out at UMIST, Manchester but. so far as we know, not published.20

This method could not be tested, since the pilot plant is not yet functioning.

2.7 Paper splitting

This method has been devised by Wachter and developed at the Deutsche Biicherei in Leipzig.3,10,12,13,24-26 This method of deacidifying and consolidating paper is used at the Deutsche Biicherei and at the Library of the University of Jena. The advantages of the method are: reinforcement, deacidification, loss repair, disinfection, sizing and reversibility. The disadvantages are: lengthy treatment, the need to remove the bindings, an increase in the thickness of the volume3 and the need for rebinding.This method has not been further investigated, since it is not really a mass system.

3. COMPARISON OF THE METHODS TESTED 3.1 General descriptionWei T'o. The Wei T'o method was devised and developed by Smith, from the 1970s onwards.3,6,10-

14,27-35 On 10 October 1989, Union Carbide Chemicals announced the signing of a contract allowing them exclusive use of the Wei T'o patent.7,8,36-38 The system is presently in use at the Public Archives of Canada in Ottawa and at the Princeton University Library, New Jersey, USA in a semiautomatic spray system.10,13

Archival Aids. This method was devised by the Centre de Recherches pour la Conservation des Documents Graphiques (CRCDG , Paris, France starting from that developed by Smith in Canada.3,6-8,l0,l2 14,39-41 The system is in use at the conservation centre for printed books of the Bibliotheque Nationale de France, in Sable-sur-Sarthe.

Bookkeeper. This method was devised by Kundrot in 1985 and developed by Spatz, president, Preservation Technologies, Inc.3,6,10-13,16,31,35,42-44 This method was being used in a pilot plant at Orville, Ohio, USA but the plant was closed as the result of a corporate merger. There is no new plant.43

Diethyl zinc. This method was devised around 1974 by Williams and Kelly, Library of Congress.3,6-

14,16,17,31,33 35 The system is being developed by AKZO Chemical Division and its subsidiary Texas Alkyls.45-53 A pilot plant has been set up in Fairfield, Connecticut, USA; it is planned to be operational in 1991.6

BPA. This method was developed by Fairfield and put into practice by Book Preservation Associates,3,10-13,16,31,54-56 with operating facilities in Carteret, New Jersey, USA.

Vienna. This method was devised by Wachter and developed at the Osterreichis-che Nationalbibliothek1-3,10,12-14,31,57-59 where it is in operation.

FMC. This method was invented in 1988 and developed by the FMC Lithium Division. 10,31,60-65 A pilot plant has been operational in Bessemer City, North Carolina, USA since May 1990.60,66

Parylene. This method was developed at Union Carbide Corporation/Nova Tran Corporation by Humphrey from 1984 onwards.67-71 Only consolidation of the paper is involved. A pilot plant has been established at Clear Lake, Wisconsin, USA.

3.2 Treatment3.2.1 Selection bejore treatmentWei T'o. Selection is based on the vulnerability of certain inks and colours. In all, this represents, according to some,13 20-25% and for others, only 3%.10,11,28 Banik' quotes both sets of figures. Schwerdt8 cites 30% rejection. A librarian makes the first selection, the most important, and the second is carried out in the treatment area. The book format is limited to 21 x 25.5 cm,32 30x37.5 cm14 or 24 x 45 cm.27,29

Archival Aids. About 30% are rejected.6 The format is limited to 28 x 18 cm.39

Bookkeeper. In theory, no selection is required but reds are sensitive to the treatment.11,42 No mention of limit on format. We have to wait for the new plant to determine the dimensions of the chamber.

Diethyl zinc. In theory, selection is not needed,10,11,16,17 but coated paper must be treated separately.3l,51,52 Drying some papers takes longer.6 No limit on format.11

BPA. Minimal selection to remove leather bindings.55 No limits on size.

Vienna. Before the treatment proper begins, it is necessary to remove the bindings. Format is limited to 52 x 40 cm x 4 cm thick.2 This method is theoreti-

cally reserved for newspapers but there is no reason why it should not be applied to other printed material.

FMC. No selection and no size limit.

Parylene. No selection and no size limitation. For some covers it may be necessary to use an adhesive to facilitate the attachment68,69 of the polymer.

3.2.2. Treatment details

Wei T'o. The deacidifying agent is CMM. The treatment begins with a dehydration stage to reach a residual moisture content of 0.5% in a vacuum chamber heated at 58°C for 26 h29 or at 50°C12 to 60°C.11,28,30 for 36 h.11,12,28,30 Treatment is carried out in a vacuum chamber and lasts for 308 to 5029 or 60 min.30 The solution is sold by Wei T'o, CMM in methanol (8-10%)l2 diluted to about l:106,8 with a mixture of trichlorotrifluoroethane (Freon® 113, TCT-FE) and dichlorodifluoromethane (Freon® 12, DCDFM).11,13,31 After treatment the excess solution is recovered and returned to Wei T'o for recycling.8,11,27,29 The books are left to dry for about one hour.8 The last stage is conditioning of the treated books placed overnight in cardboard boxes in a ventilated room.11,28,30

Archival Aids. The deacidifying agent is CMME39 and no longer CMM, as in Canada. The description of the method is based on information provided by the centre at Sable-sur-Sarthe.39,40 The first stage is dehydration, to arrive at a residual humidity of 0.5%, initially in a ventilated chamber for at least 12 h at 60° C then in a vacuum chamber also at 60°C for at least 20 h. Treatment is carried out under pressure in a heated autoclave at 20-30°C. for 15-30 min. The solution required is sold by Archival Aids: CMME in methanol and ethanol (20%). This solution is diluted down to 2% with CFC. Excess solution from the reaction is recovered and can be reused 2-6 times. According to Schwerdt,6 the concentration of CMME is 8-12% and this basic solution is diluted 1:46 or 1:58 in the CFC and used 4 times.6 Afterwards the solution is distilled to recover the CFC and the residue (CMME, ethanol and dirt from the paper) thrown away.39 According to Schwerdt,6,8 recovery of the solvent is not optimal. The last stage of treatment is drying, which is carried out in a ventilated area, at room temperature, for 24 h.39

Bookkeeper. The deacidifying agent is magnesium oxide powder in suspension in TCTFE plus a surfactant. Research is in progress into the possible use of a

hydrogenated CFC (HCFC).43,44 The concentration is 0.2-0.3 g/142 to 1.5 g/1.44 No preliminary selection10,11,17,44 or dehydration3,6,10,11,17,32,44 is required. For treatment the books are placed on their spines opened up at angles from 90° to 120° and moved from bottom to top. After the air is evacuated for 15 min, the dispersion of magnesium oxide is added for 5 min and then followed by evacuation of air again, this time for 60 min, after which up to 95% of the TCTFE is eliminated. After the books are heated in a vacuum for 5 min, the residual TCTFE has been removed. According to the description by Spatz,44 the books are treated at an ambient temperature (24°C and 60% relative humidity) for 10 min and dried under the same conditions.

Diethyl zinc. The deacidifying agent is gaseous diethyl zinc. To attain a residual moisture content of 0.5%, there is a preliminary dehydration stage in a vacuum chamber at 40°C for 18-20 h14,52 or 25-30 h.6,8,12,13,51 According to AKZO,35 this first stage of the treatment lasts for about 32 h, including a final purge with nitrogen. The treatment is carried out at low pressure in an autoclave heated up to 65°C.51. This phase lasts 6-9 h8,13,14 or 10-12 h12,52 Several purges with nitrogen then follow, the total procedure lasting 16 h.35

The product of the reaction using diethyl zinc is ethane, which is evacuated from the chamber; excess diethyl zinc is removed and the residual zinc oxide forms the alkaline reserve. The treated material is then reconditioned using water vapour and carbon dioxide. About 75% of the initial paper moisture content is attained within 6 h12,52, 6-9 h11,13 or 12 h.14,35 The material is then brought back to atmospheric pressure.

BPA. The deacidifying agents are the mono-, di- and triethanolamines. The system is gaseous, based on ethylene oxide, ammonia and water vapour (a system long used for sterilizing medical equipment). No dehydration is necessary. The treatment is carried out under a partial vacuum at 37.7°C and 70% relative humidity or at 36.7°C and 50% relative humidity.11,56 Ammonia is first vaporized inside the chamber, and this atmosphere is maintained for 4 h. A noninflammable mixture of ethylene oxide and Freon is then introduced; this stage lasts 18 h.56 Finally, the chamber is evacuated, then rinsed several times with air to remove any ammonia or ethylene oxide that had not reacted (25 times) and the chamber is returned to atmospheric pressure.10

Vienna. The solution is based on calcium hydroxide (at different pH)58,59 and methylcellulose (0.1%). Treatment is carried out in a vacuum autoclave. The books are immersed for 2 h and then pressed. The following stage is freezing at — 30°C, which takes 5 h. The books arc then dried by lyophilization over

a period of 2 d; the temperature is gradually raised to 70°C. Finally, the books are replaced in their original bindings or, less frequently, in a new binding.57 According to the description of the treatment given to our samples, the immersion lasted 4 h (solutions at pH 8.7 and 9.5), pressing 10 min, freezing 1 h and drying 3 d at room temperature.59

FA1C. The deacidifying and consolidating compound, MG3, is a nonpyrophoric magnesium compound soluble in hydrocarbons and halogenated compounds.62'64 No alcohol is used. A similar compound, based on zinc, has also been studied. Some binders (long polyfunctional chains) are attached to magnesium and then interact with the hydrogen bonds of the cellulose for reinforcing the paper. These binders are made from butoxytriglycolate.62 The concentration of the solution is 0.05 M in TCTFE.63 The first stage is dehydration, to reach a residual moisture content of 2%, using dielectric heating at 50°C under vacuum.62,63,65,66 This takes 3 h. The second stage is impregnation with MG3 for 10 min. The excess solvent is removed under vacuum. Finally, the books are taken out of the treatment chamber at room temperature61'63 and are dried by dielectric heating at 55°C for 3 h.63,65,66 The books are taken for treatment from libraries and placed spine downwards in sealed containers, and return there with the packaging intact.

Parylene. The consolidating compound is parylene N. a polymer derived from xylene.68 The treatment is carried out in the gaseous phase under medium vacuum and without solvent. First, the parylene dimer (di-paraxylylene) is heated at l5O°C and begins to sublime. Through pyrolysis (at 650°C), the dimer is divided into two reactive monomers.69 Under the influence of pressure, the gas penetrates into the chamber where the object to be treated is placed. The monomers polymerize at room temperature inside the chamber.67-71 The result is the formation of a film composed of long chains of the polymer, poly-para-xylylene.68 No preliminary dehydration is required. Treatment is carried out in a cylinder (diameter 35 cm and height 43 cm but its size can vary.69 The book is placed vertically in the chamber on a support that keeps it open at 180°. Under the influence of pressure, the pages open in a regular fashion, like a fan.70

3.2.3. Length oj treatment

Wei T'o. Deacidification takes 1 h.28,30,32 A complete cycle would take 43-53 h.

Archival Aids. Deacidification takes 30 min39,40 and the complete cycle takes at least 56 h.

Bookkeeper. Deacidification takes 5 min and the complete cycle 2.5 h,10 3 h12,16,42 or 4-5 h.6,13

Diethyl zinc. Deacidification takes about 8 h and the whole process needs 45—55 h6,,13,- 55-60 h14,52 or 62 h.35

BPA. The total length of treatment is either 24 h12 or 36 h.10

Vienna. The deacifidication stage takes 2 h and the whole procedure takes at least 55 h.

FMC. The three-stage treatment lasts 6 h.6l,63

Parylene. The time needed to consolidate an average-sized book is 5-6 h.69

3.3. Results3.3.1. pH of paper

Wei T'o. 7.5-8.5i8 or 8.5-9.5.6,8,13,14 The values obtained vary depending on initial values.11

Archival Aids. Between 5.8 and 9.7.12 5.0-6.0 near the spine and 7.6-10.0 on the outer edge3. The pH values obtained at the Battelle Institute are between 7.2-10.5.6 The values increase significantly over initial values but are not uniform on a single page3 or through a book.6 The reasons for this lack of uniformity could be poor contact between the solution and the book or the initial quality of the paper.12 No information is available concerning the actual treatment with CMME.

Bookkeeper. 7.2-8.410,42 or 8.0-9.0:3,6,17 The values increase significantly but are only uniform if the drawer is shaken.3,10,12,42 In Smith's opinion16 the results are not uniform. There is some doubt about the extent of penetration into the paper structure.3161' Deacidification is not immediate and comes about through reaction between the paper's acids and the magnesium oxide particles.3,10,l3,31

According to Schwerdt6 the neutralization is slow and constant and the results uniform.

Diethyl zinc. 7.0-7.56,14,35 or 7.0-8.5.11 Neutralization is uniform,3,11-14,17,32 except according to Thompson,34 and complete.6

BPA. 7.0-9.0,10 7.5-9.011,55,56 or 8.0-9.0.3 The results are uniform,10,11 both through the book and over the same page. The pH remains stable during dry accelerated aging (AAD).56

Vienna. 5.7-9.0, and the uniformity of treatment could be improved.3

FMC. 7.0-8.010 or 8.0-9.563.

Parylene. Consolidation treatment only.3.3.2. Alkaline reserve of paper

Wei To. Uniform alkaline reserve about 0.7-0.8%13,14,17 or 0.8-1.2%.37 According to Schwerdt,6 the quantity of alkaline reserve conferred on the paper is difficult to calculate.6

Archival Aids. Alkaline reserve using CMM is about 0.22—1.12% and considered satisfactory.12 The Battelle Institute found reserves of 0.03-1.5%. Neutralization is not uniform and the reserve is insufficient.'1 Same comment as for Wei T'o.6 No information on results using CMME.

Bookkeeper. Alkaline reserve about 2%.17

Diethyl zinc. Satisfactory12 alkaline reserve, about l-2%35,47 or 1.5-2%.6,14 For others13 this would be insufficient. The alkaline reserve can be calculated with a certain degree of precision according to the moisture content of the paper6" within the range 0.5-3.5%.52

BPA. Alkaline reserve about 1%3 or 0.85-2.14%.31,56 Vienna. No information.

FXIC. Alkaline reserve about 1.5—1.7% for the compound based on zinc and 2.1 -2.3% for that based on magnesium; uniform results.10,61 The alkaline reserve after accelerated aging, humid (AAH) was 0.2%.72

Parylene. Consolidation treatment only.

3.3.3. Mechanical resistance of paper

Wei T'o. Tests carried out in Japan on papers artificially aged then sprayed with the solution found little effect from the deacidification.33 Good results were reported by the inventor.6,13,27 The mechanical resistance of acid papers was improved after treatment and after AAD according to tests carried out for Union Carbide.38

Archival Aids. From tests carried out on newsprint deacidified with GMM, strength was improved after AAH.12 No information from use of CMME.

Bookkeeper. From tests carried out by the promoter, mechanical strength was improved after AAD and AAH.10,13,42 For others they were unaffected.12

Diethyl zinc. From tests carried out in Japan on artificially aged papers, the results were fairly bad after AAH and worse than those obtained using the Wei T'o spray.33 According to others, the results were satisfactory, even increasing after accelerated aging.13,14 Double-fold values increased from 3 to 5 times after accelerated aging.6,13,14,52

BPA. Mechanical resistance is good13 or even improved,10,13 especially with wood pulp paper.3,56 After AAD double-fold measurements are higher.55

Vienna. Tests on tensile strength, breaking length and stretch at break gave good results.2,3

FA1C. The mechanical strength after accelerated aging (AA) was improved 10-12 times.10,61,62 It varied depending on the paper's condition.63 The results from independent testing after AAH were good.72

Parylene. Tensile strength varies in relation to the thickness of both the support and the applied film of parylene;68 it increases even when the film of parylene is very thin.71 On accelerated aging, the treated paper degrades if it has not previously been deacidified.72 If first deacidified, then its behaviour is excellent.69

3.3.4. Odour of paper

Wei T'o. No smell13 or solvent smell in the books for a day14 or several weeks.6

Archival Aids. Smell of the solvent in the books for several days.6

Bookkeeper. No smell.13

Diethyl zinc. No smell.11,31

BPA. The smell of ammonia was mentioned even after 25 air washes.30

Vienna, FMC and parylene. Not mentioned.

3.3.5. Surface deposits on paper

Wei T'o. There could be white deposits on the paper.6

Archival Aids, Bookkeeper, diethyl zinc, BPA, Vienna, FMC and parylene. Not mentioned.

3.3.6. Yellowing of paper

Wei T'o. Wood pulp paper can yellow.11,14

Archival Aids. Yellowing of wood pulp paper has been observed.12

Bookkeeper. Brightness is slightly improved.10

Diethyl zinc. The photosensitivity of zinc oxide to UV light should be studied in more depth.3,6 But this would be a negligible factor, considering the quantity of UV radiation actually present in a reading room.10

BPA. Treated paper yellows slightly,10 especially when it contains lignin.11,55

Vienna. Treated papers yellow slightly but less so than they would have done during natural aging if left untreated.57 Methylcellulose slows down the oxidation of lignin present in mechanical pulp papers.1-3 Washing the paper also has an effect.1,2,10

FMC and parylene. Not mentioned.

3.3.7. Effect on inks

Wei T'o. Movement of some inks or colours possible.3,11-14

Archival Aids. Bleeding of some inks and colours noticed when using CMM.6,10,12 Information is lacking for CMME.

Bookkeeper. Some marker pen inks could sometimes give problems.10,42 Information is lacking1' but, according to Spatz,42,44 there are no problems.

Diethyl zinc. White deposits have been seen on inks.31

BPA. According to Howe55, there are no effects on inks and colours, nor on plastic laminates. Coloured covers may discolour.10

Vienna. No adverse experiences, but it is necessary to test before treatment.2'3 Parylene. No change in inks or dyes.69

3.3.8. Effects on leather bindings

Wei T'o. These are not treated, given the essential preliminary dehydration.12,14,32 According to Schwerdt,6 leather bindings are treated. According to Begin," the treatment has no visible effect on the bindings.

Archival Aids. Leather bindings are treated but not plastic covering materials.39

Bookkeeper. Treatment of leather bindings is neither mentioned nor discouraged. It is noted that red cloth bindings could present some problems.10'42

Diethyl zinc. No effect on leather.11,14,47

BPA. Not treated since there is a possibility of gelatinization.10,11 Tests are being carried out to determine whether such bindings could be treated.31,35

Vienna. Covers are removed first. FMC and parylene. Not mentioned.

3.4. Output

Wei T'o. In every cycle 2 baskets containing 20-30 books are treated.628;29'32 About 150 volumes could be treated daily,'3 with an estimated annual capacity of 42,00013 or 43,200 volumes.14,31 In full production, from 150,00013 to 200,00014 volumes per year could be expected.

Archival Aids. In every cycle, 80 to 150 books; with 2 cycles per day39,40 or 8 baskets full, this would be 200 books.6 The annual capacity is estimated to be 60,000 volumes12 or 200 cycles.39

Bookkeeper. The pilot plant had a capacity of 8-10 books per cycle.6,12,J3,42 The plant being projected will have an annual production of 50,000 volumes.10,42

Diethyl zinc. The pilot plant actually functioning has a capacity of 350 books per cycle, 40,000 per year. The commercial unit being planned will have a capacity of 8,750 books per cycle, or 1 million per year.51

BPA. A total of 27,900 books can be treated daily, or 7 million volumes per year.55

Vienna. The number of volumes treated in a given cycle is not known precisely. The number treated, limited by the size of the freezing chamber, is 56 volumes weekly.2

FMC. At present, 150 books are treated in a cycle.60 The annual capacity should be 100,000 volumes if 500 books are treated daily. FMC Lithium Division has announced the construction in 1991 of a large operating unit that could treat 1-3 million books annually.62,64,66

Parylene. The present experimental production is a maximum of 12 books per cycle. A pilot plant that could treat 100 books per cycle, 400 books daily is planned. A continuous production system is also Being studied. This would have a production of more than 1000 books daily, about 500,000 annually.68

3.5. Cost per book

Wei T'o. USD 3-4,27,34 USD 3.5-4.5,31,32 USD 3.5-67,9,14 or USD 7.35

Archival Aids. USD 2 for the solution.40 Depending on the number of books treated daily, treatment will cost USD 0.02-0.06 per leaf.15

Bookkeeper. USD 4-610,35 to USD 5.44

Diethyl zinc. USD 3.5-5,6,8, 13,14,35,52 USD 6-1047,50 or USD 1O-15.9 Transport costs should be added to these figures.

BPA. USD 3,55 USD 2-7.531 or USD 3-5.10

Vienna. No costs are given, only that of the installation - USD 650,000.2

FMC. USD 3-10.65

Parylene. USD 40~100.69 This could be reduced by a new process for producing the dimer.71

3.6. Staffing

Wei T'o. Two operators.6,29

Archival Aids. Two storeroom workers and one technician.12,39 Bookkeeper. Two technicians.44

Diethyl zinc. An engineer, some operators, technical chemists and maintenance workers.14 For a commercial unit the total would be 11 people.51

BPA. No information available. Vienna. Two unskilled workers." FMC and parylene. No information available. 3.7 Safety

Wei To. The system is said to be safe because the product used arrives and leaves in the original cylinders fitted with safety valves. The product itself is noninfiammable and nontoxic.6,8,l0,14,l6,29

Archival Aids. The treatment is carried out in a ventilated area fitted with detection systems for both methanol and Freon.39 No mention of the toxicity of the system.

Bookkeeper. As there is no chemical reaction, the system must be safe.10 The toxicity of the system remains to be investigated,13 but there should not be any toxic by-products.l0,44

Diethyl zinc. The system is considered unanimously to be dangerous but, undertaken by a specialist firm, it could be safe.3,8,10 AKZO35,51 considers it to be safe. The by-products formed are zinc oxide and ethane. Zinc oxide would not be toxic for the reader.10,31,35,51,52 There are no regulations on the atmospheric emission of ethane in the United States.10 Any effects on the environment would be minimal.51

BPA. The treatment is safe, being carried out in a industrial and commercial infrastructure supplying controlled personnel and under computer control. There would not be any toxic by-products, the ethanolamines produced are also present in domestic products, and the quantity produced is below the safety standards.00 There is some concern about the ethylene oxide.12,16,34 The system is in a closed circuit and there should be no gas leak.10

Vienna. No solvent or inflammable product is used.

FMC. The toxicity of the system has been studied by its promoters. The treatment is safe.61,63

Parylene. There is very little risk of contact with the chemical products dangerous to the workers.'4 It is not poisonous either for the workers or for the readers.69

Chloroflurocarbon problems

Wei T'o. There would still be a lot of CFC in the books after treatment.6,8 The solvents are recovered30 but the treatment must be studied using another solvent.8,11,13,14

Archival Aids. As for the Canadian method, there is a problem with CFC.6'8 The Freon 12 should be replaced by a "soft" CFC, perhaps chlorodifluorome-thane?10

Bookkeeper. CFC will not be used but HCFC 123, whose possible toxicity is being studied, will.43

Diethyl zinc. No CFC involved.

BPA. The CFC could be replaced by carbon dioxide.31

Vienna. No CFC involved.

FMC. The commercial firm is prepared to use the 'soft' CFC as soon as they become available.62,63 HCFC 141 6 and 123 should be used in 1991. The present system is a closed circuit with recovery of the materials.

Parylene. No CFC.

3.8. Independent testing

Wei T'o. The Battelle Institute has evaluated the method but without tests.6 Oye33 has tested the Wei T'o product by vaporizing the aerosol; could the results obtained be compared with those measured after an autoclave treatment? Union Carbide Chemicals has also had tests carried out by an indepen-dent laboratory.38

Archival Aids. The Battelle Institute has carried out some tests on a sample of 80 books.6 Information is lacking on treatment with CMME.

Bookkeeper. No results from independent tests.

Diethyl zinc. The Battelle Institute has evaluated the method but without tests.6 Oye33 has tested diethyl zinc by comparing it with Wei T'o spray.

BPA. No information from independent tests.

Vienna. Independent tests carried out by GLV, Vienna3 but so far as we know, no published information.

FMC. Tests were carried out by the Institute of Paper Science and Technology to measure mechanical strength and any chemical effects of the treatment.10,61-63,72:

Parylene. The method of consolidation of objects is used at the Canadian Institute of Conservation, Getty Conservation Institute and the American Museum of Natural History.68,69

3.9. Advantages

Wei T'o. The system is considered to be simpler than diethyl zinc, cheaper, safe, nontoxic, requires few staff and can be installed within the library area itself.

Archival Aids. Solution reusable and recyclable, cheaper to run than diethyl zinc, requires few staff and an infrastructure compatible with that of a library.

Bookkeeper. No drying required, simple system, efficient, odourless, low cost, quick and with an infrastructure compatible with that of a library.

Diethyl zinc. Efficient, uniform treatment, without smell, fairly safe, fungicidal action, usable on different types of paper, ink, adhesive and leather.

BPA. No drying required, little handling and simultaneous disinfection.

Vienna. Elimination of acidic degradation products, method for reinforcing newspapers and an infrastructure compatible with that of a library.

FMC. Mechanical strengthening of the paper, no selection required and no handling.

Parylene. Reinforcement of some very fragile papers and no problems with inks.

3.10. Disadvantages

Wei T'o. Selection necessary (inks and leather bindings), uniformity difficult to achieve, low alkaline reserve, residual odour, limited capacity of the treatment chamber and limitations also imposed on format.

Archival Aids. Selection for inks, uneven pH and alkaline reserves, residual odour.

Bookkeeper. Selection (for marking inks), deacidification only on the surface and not within the paper, lack of uniformity through the book.

Diethyl zinc. Selection (coated paper), expensive treatment, lack of information on its stability and efficacy, treatment outside the library.

BPA. Selection (leather bindings) and residual odour.

Vienna. Selection (inks), taking down and rebinding books, a system that is not truly mass.

FMC. Treatment outside the library.

Parylene. No deacidification, paper becomes hydrophobic and the treatment is irreversible.

3.11. Improvements suggested in the literature

Wei To. It is necessary to: improve the solution to decrease the problem with soluble inks,13,14 develop a system for direct recovery of the working solutions so that they can be used directly11 and resolve the problem of CFC.6,13,14

Archival Aids. The solution must be improved to get more uniform results,3 improve penetration into the book,12 improve recovery of the solution to protect the environment,6,8 reduce the drying time10 (with microwaves6,8), automate the system10 and simultaneously reinforce the paper.12

Bookkeeper. It is necessary to study penetration of the particles,3,11,13 the distribution of magnesium oxide11,17 and long-term effects.3,13

Diethyl zinc. Reduce the dehydration period,8 study the long-term behaviour of zinc compounds8,13,16

and evaluate the problem of photosensitivity.3,6,13,16,31

BPA. Study the consequences of the use of ethylene oxide.3,11,16,54

Vienna. Improve the solution to obtain a more uniform neutralization and higher alkaline reserve3,10 and change the installation to achieve a truly mass treatment10

FMC. Nothing suggested.

Parylene. Develop a mass system,3,10 improve the uniformity of the polymer distribution and study its stability.5

Table 2. Characteristics of the selected methods

Table 3. Technical information on the selected methods

Table 4. Technical parameters of tested methods

4. CONCLUSIONSDespite the numerous studies dedicated to mass treatments, it is clear, as could have been expected, that there is still no miracle method. It is also clear that many questions still remain unanswered:

Wei T'o. Can books be left for more than 24 h at a minimum temperature of 50°C? Can the length of the cycle be reduced? Does the paper's mechanical resistance improve? Can paper containing lignin be treated? What is the precise cost per book? Has the problem of CFC been resolved? Is the system completely safe and nontoxic?

Archival Aids. Can the books really be kept for 32 h at 60°C? Can the length of the cycle be reduced? Has any testing been carried out to evaluate the use of CMME? Are the pH values and alkaline reserves uniform? Can paper containing lignin be treated? What is the precise cost per book? Has the problem of CFC been resolved? Is the system absolutely safe and nontoxic?

Bookkeeper. Are the results obtained uniform? Is the deacidification complete? What is the precise cost per book? Has the problem of CFC been resolved? Is the system absolutely safe and nontoxic?

Diethyl zinc. Can the books be kept for more than 10 h at more than 50°C? Can the length of the cycle be reduced? Can the photosensitivity of zinc oxide be accepted even if the books are kept in the dark? Do the books always have to be kept in the dark? What is the precise cost per book? Is the system absolutely safe and nontoxic?

BPA. Can the length of the cycle be reduced? Can paper containing lignin be treated? What is the precise cost per book? Is the system absolutely safe and nontoxic?

Vienna. Is it possible to reduce the length of the cycle? Are the pH values and alkaline reserve uniform? What is the precise cost per book?

FMC. What is the exact cost per book? Has the problem of CFC been resolved? Is the method absolutely safe and nontoxic?

Parylene. Can the treatment be combined with a mass deacidification technique? What is the precise cost per book?

The proposed treatments are still not perfect. Many improvements should and must be made. It also seems that, in the future, the perfection of a method of mass treatment will no longer be the responsibility of either a library or a conservation centre but rather that of a multinational chemical company. This could perhaps be an indication of safety, but by no means must this mean neglecting collaboration with curators and conservators with regard to their specific requirements. Finally, the last requirement is evaluation of the methods. Individual testing of every method, and for different types of papers with either dry or humid accelerated aging is not enough. On the other hand, the results of tests comparing the different methods using the same paper samples are not yet available. Studies of this type are in progress in different institutes,75 especially at the Institut royal du Patrimoine artistique, and the results from such studies should guide conservators in making their choice.

SUMMARIESA Bibliographic Survey of Mass Deacidifuation MethodsFifteen methods for mass deacidification are described. Their basic techniques are reviewed as well as their advantages and disadvantages. Published information on the methods being evaluated practically has been supplemented with information obtained through contacts with the treatment centres.

Synthese Bibliographique sur les Traitements de MasseQuinze methodes de traitement de masse sont presentees. Leurs caracteristiques techniques sont passees en revue ainsi que leur? avantages et leurs inconvenients. Les donnees publiees pour les methodes en cours devaluation sont completees par les informations rec,ues lors des contacts avec les centres de traitement.

Massenneutralisierung im Überblick aufgrund veröffentlichter BerichteAulgrund der einschlägigen Yeröffentlichungen werden die technischen Grundlagen sowie die V'or-und Nachteile von fünfzehn Yerfahren der Massenneutralisierung beschrieben. Bei sieben von ihnen werden die Angaben aus der Literatur ergänzt durch Informationen, die im direkten Kontakt mit ihren Betreibern bzw. Entwicklern eingeholt wurden.

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Anne LienardyInstitut royal du Patrimoine artistiquePare du Cinquantenaire, 1B-1040 BruxellesBelgium