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and more acidic the paper is, the more brittle it is.
It is even possible to make a correlation between
the pH, age and brittleness (3 hand folds or less)
if the period 1800-1850 is excluded because of
inhomogeneity due to rag fibers still in use.
From this collection’s specific correlation (see
formula in fig. 4), we can calculate at what age a
specific paper in our library with a specific pH is
likely to become so brittle that it no longer can be
handled without risk of disintegration. This stage
(“End of Life”) is defined as the paper breaking in
3 hand folds or less. A paper with pH 5 will go into
“End of Life” 160 years after the year of production.
This is close to the results from a survey in Slovenia
presented by Kolar [6]. Since we know the pH and
the year of production for each of our samples we are
then able to estimate the remaining lifetime of all of
our books, maps and manuscripts if the environmental
conditions in our repositories remain the same in the
future as today. As shown in figure 5, it is only 88.6%
of the objects from the modeled period 1850-1985,
which are acidic. The remaining 11.4% of the objects
are not acidic and can be maintained much longer.
As many as 26% of our acidic objects will reach an
advanced degradation state in 2050 if the collections
pH
84
10
9
8
7
6
5
4
3
2
1
remain in the environment in which they have been
stored until 2006, 80 % in two hundred years (in
2200) and in 2400 all our acidic objects will have
degraded and may not even be possible to handle in
the reading room.
Lifetime prolongation
With the knowledge we have today, there are two
ways we can go to about prolonging the life of the
collections. The rate of degradation can be lowered
if we either neutralize the acid in the paper (mass
deacidify) or store the paper in a colder and/or dryer
environment as the chemical reactions (hydrolysis
and oxidation) are then slowed down with no
change of the chemical state. Or both measures can
be taken.
Mass deacidification is a chemical treatment
neutralizing the acid in the paper on a large scale.
Besides neutralization, the treatment deposits a buffer
to prevent future acidification, thereby preventing the
materials from becoming more brittle. Till now the
process cannot restore the paper’s original strength
– it can only slow down further degradation, but
international research has focus on this area. In fig.
y = 0,0097x + 3,4855
0
0 20 40 60 80 100 120 140 160 180
Age
Fig.4. Here the surveys proportion of very brittle objects, which breaks in 3 hand folds or less, from the period 1850-1985 are plotted
against pH and age. The line of correlation is y=0.0097x + 3.4855.
3
6
9
Not brittle
Lineær (3)