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Figure 3: Correlation of EWO response (Eq. 2) and PUR (Eq. 4) and PES (Eq. 5) response using input from measurements in 20 room
locations for 4 periods of three months in 10 European museums from the EU project MASTER. The figure shows the measurement
results from the MASTER locations in relation to tolerable levels determined for the EWO for different types of locations at RH = 55%
(Table 2). The determination of the first level, “Archive store” was based on the dose response equation for showcases (Eq. 1), for
which the measurement results are not shown in the diagram.
in Table 2 are more stringent than the demand may be
for other materials, and an “error” of keeping to these
levels will only give additional protection, although
possibly at a price. As the levels in Table 1 and 2 are
determined to be practically achievable, a general
simplification of the approach to meet such “best
standards” seems reasonable.
It is important to note that the RH dependence of the
tolerable levels in Table 1 and 2 are a simplification
based on RH / T isoperms valid for paper material.
This may not be appropriate for modern synthetic
materials. The RH dependence may be different. The
RH / T interdependence, from RH = 45% to RH = 65
%, in Eq. 4 and 5 was calculated to be a change of
1.2 °C for PUR and 1.4 °C for PES, using average
values for the environmental parameters measured
indoor in museums in the MASTER project and the
64
PUR and PES responses calculated from those values.
The comparable temperature change in Table 1 varies
from 2.6 to 2.8 °C. Thus, the humidity response of
these synthetic polymers is about half that of paper.
This can be accommodated in Table 1 by reducing
the T / RH variation to this value.
EWO assessment of degradation
risk of modern synthetic materials
– based on direct comparison.
Another possible approach is to directly compare
effects on the EWO with those on the modern synthetic
polymers. To know if the effects can really be compared
it is then necessary to know how the environment
reacts with the modern synthetic polymers, preferably
by detailed dose-response equations such as Eq. 4 and
5. A comparison of Eq. 1 and 2 for the EWO with Eq.