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Current research focuses on:
With all other factors accounted for, pH still has the most dominant role in paper stability. When pH was correlated with both the yellowness index and degree of polymerization, it was determined that the lower the pH of the paper the more brittle and degraded the paper will be. Higher gelatin content levels (5.5 - 11.4 %), exhibited higher pH levels while lower gelatin content levels tended to have a range of low and high pH values. Therefore, high gelatin content papers tended to be in good condition while low gelatin content papers exhibited a range of stability from good to bad. Paper samples with high metal content that tended to lower the pH levels, Al, K, and S, were found to be less stable than those with lower metal content. For more information: |
The
condition of naturally aged papers can vary greatly based on the manufacturing
process which has changed considerably over the past five hundred years
altering the chemical composition of the papers. Some aged papers have quickly
yellowed and become brittle while others remain white and strong with age. The
reason for this stability is not fully understood, but there is a belief that
certain factors--such as gelatin content, pH, trace metal content, and
cellulose purity--play an important role. Initial studies by William Barrow
(1963) indicate that pH plays a significant role in the long term stability of
paper. However, further studies are required to determine if the other factors
listed above also have a role in the overall stability of naturally aged book
papers. In this current study, forty naturally aged papers dating from
1477 to 1793 were analyzed.