Series editors' preface - Wood Tools

188 Conservation of Furniture
teins maintain a pale blue/lavender fluorescence,
even after extensive exposure. De la Rie
(1982) showed that sandarac, dammar, mastic,
Venetian turpentine and drying oils shift from
this bluish fluorescence to yellowish after natural
ageing. Larsen et al. (1991) has observed
that fresh, unbleached shellac immediately
fluoresces orange. The UV fluorescence of shellac
shows a variety of colours as is reported by
Baumeister (1988), Hering and Buchholz (1990)
and Wolbers and Landrey (1987). Larsen et al.
(1991) has reported changes in emission spectra
from orange to yellow for two separate lots
of orange shellac film. One film was 38 years
old and the other was recently cast. Orange
shellac can contain up to 10% dyestuffs (Mills
and White, 1987). If this dye was originally present
in both samples in approximately equal
amounts and after 38 years it had begun to
fade, it is possible that the observed shift in fluorescence
is associated with fading of the
dyestuff and not solely indicative of lot variance.
Optical microscopy is frequently the first
method used when further investigation of
paint samples is necessary. Transmitted and
incident microscopy can be used to view the
stratigraphy of the organic materials that make
up these complex coatings. The layer stratification
can be studied in areas of losses or, if
sampling is possible, on an embedded crosssection.
Sample removal techniques, mounting
and examination of cross-sections taken from a
broad range of paintings representing different
artistic techniques are described by Plesters
(1956). Waentig (1993) has a range of casting
materials. The mounting of samples from a
polychrome sculpture using a polyester casting
resin and a glass knife microtome to expose
the cross-section is described by Stodulski and
Dorge (1991).
Stains that are reactive towards specific functional
groups have been employed to characterize
organic adhesives, mediums and resins.
Johnson and Packard (1971) note that it is
important to first test for proteins since egg
yolk also contains a significant amount of oil
that would in addition test positive for oil.
Martin (1977) makes visual observations while
heating a thin section to 225 °C to detect oils;
since resins may degrade in appearance similar
to oils she used bromo creosol purple to
first test for resins. It is necessary to test the
sample with this stain prior to embedding since
this is a non-specific stain for acids and will
react with acids commonly found in embedding
materials. Wolbers and Landrey (1987)
has used fluorochromes to test for triterpenoid
resins. The reactivity of fluorochrome stains
can be difficult to determine when pigments
interfere with the auto fluorescence of the
medium or on occasions where absorbent passages
have localized intensities of dyes present.
To reduce this false-positive assessment, thin
sections taken from embedded cross sections
or high magnifications (e.g. 800) may need to
be used. Even then, interpretation remains subjective
and though results may suggest the
presence of a particular substance, more
advanced methods should be used for positive
identification.
Gas chromatography (GC) will characterize
many organic materials by resolving the heterogenous
components according to molecular
composition. Glastrup (1989) and Mills and
White (1977) used GC to identify resins. White
(1978) showed that original components of
waxes and their mixtures are easily separated
and identified with GC since they are chiefly
composed of non-glyceryl esters which are
more stable than components of resins and oils.
Drying oils differ dramatically after they have
thoroughly set; Mills (1966) reports that it is possible
to distinguish linseed, poppy and walnut
oil according to the ratio of methyl palmitate to
stearate obtained from the chromatogram and in
1982 reported some success in distinguishing
stand from raw linseed oil by noting the ratio of
dicarboxylic acid esters present.
Pyrolysis gas chromatography (PGC) has
been used to identify synthetic resins and
binders by de Witte and Terfve (1982) and
Sonoda and Rioux (1990) whilst a range of
alkyds were analysed by Bates et al. (1989). De
Witte and Bates reported data that were
obtained from a gas chromatography apparatus
coupled to a mass spectrometer to enable the
identification of peaks according to their
molecular fragmentation pattern. Mills and
White (1982) has discussed the benefits of
mass spectrometry in identifying artists’ materials.
Hyphenated techniques such as GC-MS,
LCMS and PY-GC-MS have greatly enhanced
detection capabilities and separation methods.
Proteinaceous materials are too high in
molecular weight to identify easily with gas