Paper and book conservation – Part 2

Two major problems associated with old paper manufactured during mid nineteenth century onward are:

  1. Brittleness
  2. Yellowing or darkening

Breaking of paper due to brittleness (loss of flexibility to bend without breaking) generally occurs in very old paper which was manufactured from wood pulp technology.
Other feature found in such old paper getting brittle, is yellowing or browning.

Paper becomes acidic either by absorbing pollutants such as sulfur dioxide and nitrogen oxides, or because of manufacturing technique and components added during manufacturing. Traditionally, aluminium sulfate (or ‘papermaker’s alum’) was added to harden, or ‘size‘, the paper. While this gave initial strength, it was also a source of acidity. Most paper made around or after 1850 is acidic due to manufacturing additives.

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Acid catalysed hydrolysis of cellulose chains shortens the fibre lengths

The β-acetal oxygen bridge joining the glucose molecules of cellulose together is susceptible to acid hydrolysis. This breaks the chains and weakens the fibres. Paper that decomposes this way becomes hard and brittle, and disintegrates easily.

The yellowing that people typically associate with old books is unique to wood pulp paper, and it is a result of lignin, the polymer that is responsible for binding cellulose fibers together. Lignin is an integral part of wood itself and essential to the pulping and binding process of wood pulp paper, so it is an unavoidable ingredient. When lignin is exposed to the environment, it undergoes oxidation, causing it to destabilize and absorb more light, in effect turning it yellow. Although it is possible to preserve wood pulp paper by keeping it completely unexposed to sunlight, it takes only the briefest exposure to begin the oxidation process, which cannot be reversed.

 

Author: namitajaspal
Namita Jaspal, with inherited skills of art and aesthetics and passion for science, opted to pursue post- graduation in ‘Conservation of Cultural Property’ after her graduation in Science from Delhi University in 1992. Four year intense training at National Museum Institute provided the right foundation to start a career in Conservation. She is currently practicing conservation consultancy for Heritage property including monuments and collections. She has been doing independent research in conservation techniques and procedures in Indian context. She is currently working on the conservation of wall-paintings of Sri Harmandir Sahib Ji (The Golden temple at Amritsar. The project is nearing completion and getting a lot of appreciation for the organized and ethical treatment it is providing. It is for the first time in the history of Sri Harmandir Sahib Ji (The Golden Temple) that wall painting conservation and preservation is being done in a scientific manner, keeping the codes of Ethics into consideration while decision making. Another project just completed is of the Conservation of Krishna Temple at Kishankot, Gurdaspur, Punjab. In her private Conservation Laboratory, she is not only providing onservation services, but also mentoring young aspiring conservators and archaeologists by the way of training and paid internships. She has been a guest lecturer at DIHRM (Delhi Institute of Heritage Research and Management). With all the updated knowledge database and innovative practical approaches relevant to the Indian conditions, she could successfully do curative and preservative treatment of very old textiles like a nine feet long flag from nineteenth century that is regarded as priceless memorabilia of second Dogra regiment at Chandi Mandir, and four hundred years old (seventeenth century) Chola Sahib Ji of Sixth Guru of Sikhs, Sri Hargobind Sahib Ji. Apart from this she has done conservation of Photograph collections, archival records, numerous paintings, manuscripts and other cultural objects. She is also involved in preparation of up-gradation proposals for museums and such organizations. Her expertise includes Conservation and preservation technologies and procedures for conservation of varied material like wall paintings, paper, photographs, textile, ceramics, stone, metal and archaeological objects.

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