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CDNLAO Newsletter

No. 85, February 2016

Special topic: Preservation and Conservation of library materials

Evaluation of Mass Deacidification Processes for Conserving Library Materials in the National Library of Turkey

By Dr. Mehmet Konuklar, National Library of Turkey


1. Introduction

Library or archive directors have the responsibility to promote the written cultural heritage they have in possession, enhance the delivery to masses and transmit them onto the future generations by preserving them against any kind of deteriorations. The National Library of Turkey, in order to enhance the fulfillment of this responsibility, conducted research on preservation of written paper, one of the fundamental cultural heritage resources, specifically in terms of chemical factors such as acid and atmospheric contaminants.

Acidic factors that emerge within the formation or transmit from the surroundings of written papers cause deterioration in the chemical structure leading to decay and dissolution of the piece. Acidic factors might cause acceleration in cellulose hydrolysis as well as cellulose blenching by oxidation (Figure 1). In this study conducted by the National Library of Turkey, Bookkeeper, PaperSave Swiss and Bückeburg mass deacidification processes are put under examination in terms of doctrine, implementation and overall efficiency.

< Figure 1. Acid deterioration on a manuscript at National Library of Turkey >

2. Mass Applications against Chemical Deteriorations

To control chemical deteriorations on written papers, acids on the targeted papers are neutralized by increasing pH value to around 8.5, the amount of alkali reserves are raised above 2% equivalent CaCO3, harmful substances are removed so as to prevent the paper going acidic or oxidized again. Papers with pH values lower than 6.2 need to be deacidified while the deterioration levels should be kept in mind. At the present time, Ca and Mg oxides and hydroxides are widely used in order to deacidify written papers (Rychly, 2006).

Written papers are removed of acids in lab environment manually or with mass deacidification processes collectively. Sheet by sheet deacidification process is time consuming and expensive by use of injection method or submersion into basic solutions in lab environment so as to eliminate acid issue that causes deterioration in rare works as well as pieces printed on modern paper. For this reason, mass deacidification processes have been developed by institutions responsible for keeping written cultural heritage intact (Chart 1).

< Chart 1. General comparison between mass deacidification processes >
Name Deacidificant / Solvent Application Procedure Developer / User Country
Wei T’o, Sable Methoximethyl-MgCO3 / Methyl Alcohol Pre-Drying + Treatment + Ventilation Canada / France
Diethyl Zinc Zn(CH2)2 / Gas Phase Pre-Drying + Treatment + Ventilation USA / Netherlands
FMC Mg-Butyl Glycolate / Freon-13 Pre-Drying + Treatment + Ventilation USA
Papersave Swiss METE / HMDO Pre-Drying + Treatment + Ventilation Germany / Switzerland
CSC Booksaver Propoxi-MgCO3 / HFC 227 Pre-Drying + Treatment + Ventilation Spain / Germany
Bookkeeper MgO / Perfluoro Heptane Non Aqueous, Alkaline Powder Treatment USA / Canada, Netherlands, Spain, Japan +10 Country
Libertec, SOBU CaCO3 + Mgo / Nitrogen Non Aqueous, Alkaline Powder Treatment Germany
DAE NH3-Eto Gas Mixture Gas Phase Treatment Japan
Bückeburg Mg(HCO3)2 + MC / Water Immersing The Solution + Blow-Drying Germany / Czech R., Russia, Poland
Vienna Ca(OH)2 + MC / Water Immersing The Solution + Freeze-Drying Austria

The fact that mass deacidification processes are costly and could not provide the exact desired outcome raised the quantity of methods. Along with the advantages and drawbacks to each single treatment, quantitative and qualitative status of collections makes it difficult to select the deacidification process to be applied. Consequently, 6th EU Framework Program "Paper Treat – Evaluation Project of Mass Deacidification Treatments" involving many national libraries, state archives and research institutions, was put into practice between the years 2005-2008 (Kolar, 2008). In scope of the Project, parameters to be considered while choosing the deacidification method and measurement processes were studied. Furthermore, stabilization of paper samples deacidified with Bookkeeper process in normal (20°C), cooler (15°C), cold (5°C) environments were compared with untreated sample. Life cycle of papers doubled if the storage temperature is lowered to 15°C, while it rises as many as 8 times in case the temperature is lowered to 5°C. This figure goes up to 30 times with deacidification.

Here we chose Bookkeeper, PaperSave Swiss and Bückeburg deacidification processes, the three methods which were highly evaluated in the Library of Congress Technical Standards of Mass Deacidification in terms of potential for innovation, enhancement of mechanical endurance and existence, pH and alkali reserve values, and cost and risk assessment.

2.1 Bookkeeper Process

Bookkeeper acid removal process is based on placing magnesium oxide (MgO) particles onto surface of paper via perfluoro heptane. Magnesium oxide reacts with humidity found in the structure of paper to transform into magnesium hydroxide. A fraction of the magnesium hydroxide gets neutralized by acidic factors within paper while another fraction reacts with carbon dioxide in the air to turn into magnesium carbonate, which will remain as alkali reserve on the paper. Because of the reaction of magnesium oxide with water is exothermal; the temperature could go up to as high as 50°C during the process.

Within the Bookkeeper process, deacidification of average-sized books actualizes inside vertical tubes with a capacity of 12-24 books. Documents and large-size volume pieces get deacidified manually or inside horizontal tubes by spraying method. Separated into three groups, 12-24 books are placed into vertical tubes with book holding equipment in such a way that sheets could be unwrapped by the help of a ventilator. Subsequently, the air within the tube is vacuumed and MgO dispersion inside of perfluoro heptane is pumped into the tube. After 15-20 minutes, the dispersion is withdrawn and book holders are placed out of application tube into vacuumed drying tube where they will be kept for 90 minutes. As a last step, the books are separated from holders to be conditioned in open air for 24 hours. It’s possible to deacidify around 15.000 kg of books with a single vertical tube while the deacidification capacity of the treatment really depends on tube count within the system and spent working hours.

The Bookkeeper process, which was developed at the beginning of 1980’s in the USA, has been used in national archives and libraries of more than 10 countries excluding private administrations from the USA, the Netherlands, Spain and Japan. The Bookkeeper process is a reliable process which does not have a risk of combustion and blast and also does not harm dyes, glue, ink and paper itself of books. While it has its drawbacks such as possible creation of MgO clusters on the bindings of books, leaving powderish remnants on the surface of paper and dependency of the system on human performance; many scientific studies concluded that it is indeed a favorable process.

2.2 PaperSave Swiss Process

The PaperSave Swiss is developed in Switzerland as a third generation Battelle process, which is originally created by the Library of Leipzig. In comparison PaperSave Swiss, while using the same active ingredients as previous Battelle and Papersave processes, is a better process with enhanced controlling system, application flexibility and post-operation active conditioning specifics. Established firstly to serve Swiss State Archives and National Library in 2000 with 120 tons of capacity, PaperSave Swiss Enterprise now conveys transportational service into the neighboring countries.

Active ingredient in PaperSave Swiss process is a composition of magnesium and titanium etoxide [Mg(OC2H5)2 ve Ti(OC2H5)4], also known as METE, dissolved in hexamethyl disiloxane (HMDO). The process is based on the steps shown below, in which magnesium and titanium etoxide composition reacts with lowered acidity and humidity factors on the paper. Ethyl alcohol, that is a result of the reaction, is removed off during the ventilation phase, while Mg and Ti hydroxides interact with CO2 in the air to turn into Mg and Ti carbonates and stay as alkali reserves inside the paper.

Deacidification process with PaperSave Swiss process is carried out inside large horizontal tubes. Approximately 700 kg of paper is first put into the tube in metal grids and goes through predrying operation by 48 hours microwave heating. In this phase, the humidity of the paper to react with METE is lowered from around 8% to 0.5%. Afterwards, METE dispersion in HDMO is put into the tube. 2-3 hours later, the dispersion is taken away so that the pieces get dried inside the tube for 24 hours and taken out (Figure 2). For the purpose to remove the malodor of ethyl alcohol as a result of the reactions, the pieces are kept for 3-4 weeks inside conditioning cabins.

< Figure 2. Procedure Steps of PaperSave Swiss Process (Blüher and Vogelsanger, 2001) >

PaperSave Swiss process stands out for potential of innovation, pH and alkali reserve values and risk assessment. Although PaperSave Swiss process needs substantially more of a budget and working space, offers rather more work capacity, automated system and quality in deacidification performance when compared with the Bookkeeper.

In comparison with other processes, PaperSave Swiss is emphasized with its capacity to create alkali reserves and deacidification performance (Katuscak, 2008, p.18). While it could work in fully-automated mode involving minimum human interference and perform deacidification process in high quality standards, the PaperSave Swiss process has its own drawbacks requiring larger working space and budget and also causing dispersion on some colors.

2.3 Bückeburg Process

Developed by a Germany based Neschen Company in 1996, Bückeburg process has been in use for both deacidification and solidification of documents in 20 different places of the world. There are three effective compositions in Bückeburg process: the documents gets deacidified with magnesium bicarbonate (Mg(HCO3)2, fixed for inks with mesitol and rewin, and solidified with methyl cellulose. C-900 device (Figure 3) keeps the documents inside for 4 minutes firstly by carrying them into 16°C Bückeburg dispersion. Then, it dries the documents by dispatching them into the compartment where ventilators operate in 50°C for 4 minutes. The documents out of the device should be kept under pressing machine for 24 hours. With the process that needs removal of book bindings, it is possible to deacidify 400 papers of A4 size per hour (Lojewski and Gucwa 2003, p.409).

< Figure 3. Bückeburg deacidification machine c-900 >

Among the mass deacidification processes, Bückeburg is the only water-based method that enables concurrent deacidification at the same time. Its ability to mass deacidify with a mobile device at a smaller space, its use of water-based method which is harmless to the pieces and environment, its function as partial irrigation and its effective deacidification are the favorable sides of Bückeburg process. Due to these reasons, it is the most suitable way of the three methods to deacidify newspapers and newspaper-alike written papers. Its requirement to unbind the books, its augmentation of book thickness, its unavailability with torn and delicate documents, color change at red and blue colors, leak of ink, and transposition of any stamps and eventual mild crinkliness of documents are the unwanted effects the treatment might evoke.

3. Discussion and Conclusion

Chemical deteriorations in written papers become clear after a lengthy period, such as decline of endurance and darkening of color in an acidic paper and the effect of polymer and duct tape attached to paper. The measures to be taken against these kinds of deterioration are just as long-running. Therefore, status of pieces stored without proper conditions need to be determined in every aspect and actions to be taken should be applied in conformity with a definite schedule.

Institutions possessing paramount collections such as national libraries or archives need to be aware of the fact that available deacidification processes could only slow down the deterioration rate and extend paper lifespan, not entirely preventing chemical deteriorations. Moreover, it is deemed futile processing deacidification on collections when necessary actions for physical deterioration are not taken. British Library and State Archives have decided not to apply any mass deacidification processes although they have been maintaining 182 km’s of acidic pieces, developing a brand deacidification initiative, comparing and thoroughly evaluating 7 distinct mass deacidification processes (Shenton, 2006). Harmful effects to paper authenticity, technical deficiencies and costs of deacidification processes are considered in the decision. They have rather invested in advanced storage and digitization systems for the purpose of conserving collections.

Unfortunately, application of mass processes is not the ultimate solution to keep written cultural heritage away from chemical and biological deteriorations. Therefore, it should be prioritized to slow deterioration rate down and create digital copies of pieces rather than struggling to cease deterioration. From a broader perspective at the present time, letting use of digital copies while storing originals in cold, insulated, low oxygenated and sensitive humidity controlled environments is the ideal way to conserve collections against deteriorations. In this context, the National Library of Turkey, has established a comprehensive digitization center in the last few years and has been working on the modernization and improvement of storage spaces.


Blüher, A. and Vogelsanger, B. (2001). Mass Deacidification of Paper. Chimia 55, No:11, 985.

Katuscak, S., Hanus, J., Bakos, D., Vrska, M., Jablonsky, M., Holubkova, S., Bajzikova, M., Bukovsky, V. and Rychly, J. (2008). The Khnica Project in Slovakia, Durability of Paper and Writing 2, Ljubljana, 17-19.

Kolar, J., Strlic, M., Lojewski, T., Havermans, J., Steemers, T., Bruin, G., Knight, B., Palm, J., Hanus, J., Perminova, O., Nguyen, T.and Porck, H. (2008). The Paper Treat Project - Preserving our Paper Based Collections. Durability of Paper and Writing 2, Ljubljana, 11-13.

Lojewski, T. and Gucwa, J. (2003). Can Newsprint Paper Benefit from the Neschen Deacidification Treatment? WPP Paper in Archives and Libraries, 408-411.

Rychly,J., Matisova-Rychla, L., Lazar, M., Janigova, I., Strlic, M., Kocar, D., Hanus, J., Minarikova, J. and Katuscak, S. (2006). Thermal oxidation of cellulose investigated by chemiluminescence. The effect of magnesium and calcium carbonates and of different pHs. Comptes Rentus Chimie, 9, 1-8.

Shenton, H., (2006). Strategies for Mass Presesrvation Treatment, Save Paper! (s.63). Bern: Swiss National Library.

Copyright (C) 2016 National Library of Turkey