Restoration techniques

Published : Aug 17, 2002 00:00 IST

WET paper is ideal for the growth of mould. The high humidity levels and the heat provide an even more fertile ground for mould in Indian conditions. To save paper material, drying is the immediate requirement but if paper dries fully, it will turn brittle. The challenge lies in ensuring that the paper turns dry, but not completely.

The specialised technology that companies like Cromwell have developed take into account the physical properties of the material that is to be salvaged. Care has to be taken to prevent exposure to sunlight because ultraviolet rays cause the ink to fade and the paper to crumble. In fact, moisture to the extent of 4 to 7 per cent is necessary for paper to maintain its desirable properties.

Over time, four types of techniques have been perfected to recover books and other paper material which have got soaked in water. The vacuum freeze drying method (or lyophilisation) is the process of drying frozen materials by sublimation and "desorption" at low pressure (high vacuum) and at sub-zero temperatures. This method is more suitable for reclaiming delicate paper material, points out Marshall Oliver, Director of Technical Services at Cromwell.

Thermal vacuum freeze drying involves the application of heat even as the frozen material is in sub-zero temperature and in a vacuum. Marshall argues that this method is more efficient in the case of printed material. At the SVK, a single load in the machine's chamber accommodates about 3,000 volumes.

The molecular sieve drying method, a proprietary dehumidification procedure developed by Cromwell, incorporates many of the principles utilised in thermal vacuum freeze drying. The significant feature of this process is that the application is performed in a chamber under normal atmospheric conditions. Technicians can enter the chamber to monitor the results and attend to delicate materials requiring differing drying times. But this process is more time-consuming and costlier than the thermal vacuum freeze drying method.

The temperature flux drying method of removing moisture from material can also be effective. But it requires high temperatures for extended periods. Marshall points out that this process is not appropriate for the Hyderabad collection because it can promote the growth of mould. Moreover, it is a more energy-intensive, and hence costlier, method.

The rudimentary air-drying method was adopted for the first batch of more than 30,000 volumes. Books and other material were placed in an open hall in the SVK and allowed to dry. The recovery of these materials was effected by the end of 2001 after a three-month-long operation. However, this method poses several problems. Marshall pointed out that although this process succeeded in arresting the growth of mould and in removing moisture from the material, the material also suffered "irreversible deterioration". He stated that although the result is "as good as can be expected", the method leaves the books in an "unstable" condition. This crude method of drying results in uneven drying leading to deformities and cockling of books. Marshall believes that air-drying in humid conditions is an "incomplete procedure".

Sambi Reddy, secretary of the SVK Trust, told Frontline that the volumes recovered by this method are either more readily replaceable or of lesser importance in terms of historical value. In order to ensure that these collections are not lost forever, the more important portions of the collection that underwent air-drying are to be microfilmed on a priority basis.

S.V. Narsiah, who had been a close associate of Sundarayya, said that although the principles governing Cromwell's freeze drying technology employed at the SVK are fairly simple, "the ingenuity lies in the reliability and ruggedness that has been built into the machine".

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