How do you assess archaeological paper and decide upon a conservation treatment?

Material Characteristics

Paper made before the 19th century was often made by hand from linen and cotton rag materials, which are excellent sources of high-cellulose, long fibers. Sizing for the paper was made from animal hides. These papers were mildly alkaline and are more stable. At the end of the 18th century wood fiber took the place of cotton and linen. Wood fibers are shorter and have lower cellulose contents than cotton and linen fibers; additionally, wood fibers contain lignin. Producing paper made with wood fiber required mechanical action and bleaching to make it useful.

Deterioration

Survival of paper from archaeological sites is somewhat rare, and is similar to that of textiles. It generally survives due to anaerobic conditions or proximity to other materials that inhibit attack from microbial and fungal organisms or insects. Paper from drier sites is usually brittle, stained, and fragmentary and found in association with a metal such as copper. Paper from wet, anaerobic sites can survive in protected sites, but is weakened by acid hydrolysis and oxidation. Any writing is usually greatly damaged and often illegible.

Paper is an organic material and is subject to deterioration caused by chemical, physical and biological agents. Acid-catalyzed hydrolysis is the predominant mechanism for cellulose degradation and loss of strength. Acidity can come from the paper manufacturing technique. Manufacturing processes used from the end of the eighteenth century to modern times produced a higher percent of acid-rich papers than earlier techniques. Environmental acids from exposure to acidic air pollutants, acidic materials in contact with the paper, and degraded coatings, can also damage papers.

The strength of paper results from the particular chain length. Cellulose is made up of repeating units of glucose monomers and the number of glucose units present provides a measure of degree of polymerization (DP). Acids break cellulose bonds randomly often cutting the cellulose polymer in central regions. These attacks quickly weaken the fibers.

Treatment

Paper from an archaeological site will be very fragile. Immediately place between supporting layers (e.g. Mylar sheeting), store in a refrigerator, and call a paper conservator. Keep paper in the dark, as exposure to light can cause rapid fading of any inks, dyes or other pigments on the surface of the paper.

Storage

Archaeological paper must be stored in a clean, dry, pest free environment of 50% RH and 65oF. Supports to prevent damage from handling must be used. Low light levels, with no UV, should be maintained.

Additional Resources:

Kundrot, R. & Zicherman, J. (2001). “Paper Permanence” In: Beale, F (ed.) The Encyclopedia of Materials: Science and Technology. Elsevier Science: London

Sourche from; http://www.sha.org/research_resources/conservation_faqs/treatment.cfm

 

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