Proceedings e report - Firenze University Press

SORPTION OF MOISTURE AND DIMENSIONAL CHANGE OF WOOD SPECIES USED IN HISTORIC OBJECTS
The three parameter sigmoid function was used to interpret the individual swelling and shrinkage data:
n
EMC
dEMC ( ) = dmax
(2)
n n
k + EMC
where EMC is the equilibrium amount of water vapour sorbed, d the relative dimensional change at a
given EMC and dmax reflects the maximum dimensional change for wood saturated with water.
The function shows an early exponential growth at low EMC, then slows to a linear growth for the
broad medium part between approximately 5-15%, and then approaches a constant value as the
capillary system of wood is saturated with water. The dimensional change coefficients were
determined by the linear fit across the linear range of the plots and are given in Table 1.
5. Conclusions
In addition to individual sorptive characteristics and dimensional responses of wood species,
constituting cultural heritage objects, ‘general’ moisture sorption and swelling/shrinkage patterns
which would apply as a first approximation to any wooden furnishings and collections were proposed.
They were obtained from the experimental data measured for 21 historically important wood species
used in the past for panel paintings and woodcarving. Information on further wood species of interest
to the wood conservation community can be added to the database and used to constantly improve the
general relationships.
Acknowledgements
A substantial part of this research was done within the project ‘Sensor systems for detection of
harmful environments in pipe organs’ (SENSORGAN), supported financially by the European
Commission 6th Framework Programme.
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