In our second writing assignment we were asked to do a
case study on a piece of art or analytical technique used in art restoration,
conservation, etc. I happened to find a study linking two of my favorite
topics: chemistry and Buddhism. The article was about a Buddhist monastery
built between 1470 and 1472 AD in Lo Manthang, Nepal. Constructed with
wood and rammed mud, the temple has undergone multiple restorations,
particularly along the northern wall, due to several earthquakes over the
centuries. A new conservation effort began in the early 21st century
coordinated between Italian conservators and local Nepalese carpenters in order
to repair the building and clean the interior wall murals. These paintings have
intricate depictions of the Buddha and other central figures flanked by
attendants and surrounded by many smaller designs, as seen below.
a)
b)
Figure 1 a) Interior of Thubchen Lakhang Temple b) East wall mural during
cleaning (1)
A study was conducted by
Mazzeo et al to characterize the pigments used in the mural paintings through
micro-Raman spectroscopy. This technique has some tricky theory behind it but
basically, when light hits a molecule it’s photons can be altered due to an
increase or decrease in energy from the rotations and vibrations of the
molecule’s bonds. The important thing to know is that Raman micro-spectroscopy requires
only small samples for analysis and the precision of the technique enables the
analysis of individual sections heterogeneous materials like paint. In
addition, scanning electron-microscope energy-dispersive x-ray (SEM-EDX) was
used to analyze the cross sectioned samples after preparation of samples with a
thin layer of graphite. The EDX spectrometer determined elemental composition
of the samples and provided a semi-quantitative analysis based on the
intensities of the x-rays.
The results were compiled to
provide information on both the composition of the different layers of pigment
and the method through which they were applied. The blue pigments were
determined to be high quality azurite, occasionally mixed with haematite or
lazurite. There were also traces of vermilion, a red pigment, and malachite, a
green pigment, in some of the blue samples. Excluding one sample, all of the
blue paint was applied over a very thin layer of black paint, revealing one
ancient painting technique. Haematite, or anhydrous ferric oxide (Fe2O3),
and vermilion, HgS, were identified, both together and separately, in the various
red and orange-red paint samples. Vermilion was also distinguished on one
sample from along with pararealar (arsenic (II) sulfide) and orpiment (arsenic
(III) sulfide). These particles were used to hold gold leaf in place on the
Buddha’s face by a technique known as gilding in which thin gold or silver
pieces or powder are attached to an artwork. The particular gilding technique
used was very unusual compared to other murals, which employed oil mordant to
affix the metallic leaf. The brown layer in one paint sample was unable to be characterized
due to fluorescence on the Raman spectrum. Further identification of this
pigment and an unidentified yellow ochre pigment are needed. Malachite (CuCO3*Cu(OH)2)
and brochantite were determined in the green paint along with trace amounts of
azurite and vermilion. The brochantite particles were found only on the
outermost layer of the green paint and may be a result of the interaction of
sulfur in the atmosphere with the original malachite pigment. Mural preparation
and application methods, previously theorized by locals, were confirmed with
the identification of two preparation layers beneath the exterior paint.
The ultimate goal of the
researchers involved in the study was to aid in the authentication,
conservation, and restoration of these ancient Nepalese wall paintings. The major
issues in the conservation of these mural paintings are the clay dripping down
the walls from the roof of the temples and the air pollutants that may be
affecting the pigments. This research is the first step in the long arduous
process of preserving the artwork, especially since the materials and
techniques used in the initial creation were not well known previously. From
this starting point, more studies should be conducted to gain more information
about the murals to further guide conservators in how best to maintain this
Nepalese monastery for another 500 years.
Works Consulted
1. Mazzeo, R.; Baraldi, P.; Lujan, R.; Fagnano, C. J. Raman Spectrosc. [Online] 2004, 35, 678-685. DOI 10.1002.
2. Science of Micro Raman Spectroscopy. http://www.microspectra.com/support/technical-support/raman-science/35-technical-support/126-science-of-micro-raman-spectroscopy
(accessed 6/14/12). Part of Craic Technologies.
No comments:
Post a Comment