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Scientific Report 2007-2009
Condensed matter physics and biophysics
C42. Development of non-invasive methodologies for preservation,
characterization and diagnostics of Cultural Heritage handworks
Development of non-invasive methodologies for preservation,
characterization and diagnostics of Cultural Heritage
handworks. Methods dealing with the study of
works of art must be effective in producing information
on a huge variety of materials (wood, ceramic, paper,
resin, pigments, stones, textiles, etc.), must be highly
specific owing to the variability of volume and shape of
handworks and must comply with the severe conditions
that guarantee their preservation. Therefore, standard
spectroscopic methods need to be properly modulated
in order to fit such materials, while their application
area must be enlarged to include structures and models
which are unusual for physicists. The contribution to
this field by our group is based on the development and
use of a surface NMR probe, which has proven highly effective
for on-field and non-invasive measurements, with
no significant limitations on sample volume and shape.
What makes the surface NMR probe so peculiar is its
strong magnetic field gradient (of the order of 10 T/m),
as well as its low resonance frequency (about 18 MHz)
and remarkable measurement depth from the sample surface
(up to 8 mm). To date, several applications have
been developed for paper, archaeological ceramic materials
and wooden handworks. As to archaeological ceramics,
a new model has been created, which can provide
information on firing temperature of items, as well as
on magnetic properties of their pore surface and their
pore-size distribution. Such data - in the form of 2D
Laplace correlation maps - have been presented as actual
”fingerprints” of archaeological samples. These results
return the NMR perspective on ceramics characterization
in terms of firing technology and clay origin.
As to wood, one major result concerns the possibility
of assessing the moisture content by the surface probe,
which now represents a suitable alternative to the gravity
method, with the advantage of non-invasiveness and
useful information on the moisture-content/strain relation
associate to the microscopic state of water. This has
improved the understanding of wood hydration mechanisms,
so offering a chance of prediction on wood deformation
according to environmental conditions. In addition,
these features allow for the monitoring of wood
deformation by direct check of the NMR relaxation-time
distribution and, thus, may support operations of preservation
of wooden objects of art placed in museums. Another
important application has been developed in order
to check the state of paper of historical documents,
codices or printed book. The structure of paper and the
role of water have been parameterized to get information
on the state of cellulose polymerization, the distribution
of water- cellulose bonds and the formation of interfibril
water-clusters, on which many paper properties
depend. Precisely, the analysis of Laplace correlation
maps, which give information about water exchange between
their microscopic localizations has provided growing
understanding of the state of depolymerization and
formation of cross-links between cellulose chains. A simple
experiment performed by the NMR surface probe
may detect early alterations of the structure of paper,
which may act as a warning of paper degradation.
Figure 1: The mobile NMR probe examining a fresco surface.
Figure 2: The static NMR magnetic field is produced by
two permanent magnets joined by a yoke. The central coil
produces the resonant radio frequency magnetic field perpendicularly
to the static one.
References
1. C. Casieri et al., J. Appl. Phys. 105, 134901 (2009)
2. L. Senni et al., Wood Sci. tech. 43, 165 (2009)
3. M. Brai et al., Solid State NMR 32, 129 (2007).
4. M. Camaiti et al. Studies in Conservation 52, 37 (2007).
Authors
F. De Luca, C. Terenzi
Sapienza Università di Roma 95 Dipartimento di Fisica