October was a busy month and the treatment has proceeded well,
despite a number of changes in the team. Lucy Bunning has left to take up
full time employment, and both Victor Hugo López Borges and Rachel Witt have
left to work on other projects. In compensation we have been joined by
Adam Webster who is working alternating weeks with English Heritage in their
easel painting studios.
We are making good headway with the
cleaning and stabilization of the painting. Further samples have been
taken to answer specific questions about the paint structure and previous
interventions, and the first phase of environmental monitoring equipment has
been installed.
2.1
Photography Martyn Bowen has completed the photographic survey in u.v and tungsten light
before treatment. Also, three specific areas were retaken with i.r, u.v.
and tungsten. It is planned to repeat this series of photographs during
and after cleaning to provide a comparable pictorial record of the
treatment. The painting is not an easy object to photograph: it has a
highly reflective and uneven surface which has caused some difficulty with
obtaining a high quality image. Following a number of discussions on the
subject, a decision was made for the photographs to be taken only using print
film which is to be developed by hand. From selected negatives, slides and
digitized images can be produced with little loss of quality.
2.2
Data Base The use of the data base has become more routine, in particular the log
book, where individuals can add observations, and record treatment, etc.
In fact this will become a unique document providing a detailed account of the
present campaign. The new images of cross sections (taken with a digital
camera) are of a higher quality than those previously taken in slide format
which were then scanned,
and will greatly facilitate our interpretation and analysis of the paint
structure. It is planned that earlier images of cross sections will be
re-taken using the digital camera. Some minor "glitches" have
been reported back to Dr.Nicholas Eastaugh who rectifies these problems with the
subsequent monthly upgrade.
The
treatment has continued in similar manner to previously, with little variation
in the methodology.
3.1 Stabilizing
paint, plaster and stone In addition to using isinglass, an acrylic dispersion (Plextol B500) was
used where the entire paint structure is delaminating from the underlying
support. Also, lime grout (Totternhoe lime putty, sieved and diluted in
deionised water) applied by syringe or pipette has been added as a support and
gap filler, where necessary.
3.2 Reduction
of the surface coating The cleaning of some soluble black lines which appear to exist only towards
the upper edge of the painting and on the triangular sections of plaster, have proved
problematic. The cleaning of these areas was initially reliant upon the
earlier i.r photography survey. However, an i.r camera and monitor and has
proved an extremely useful aid particularly on areas not covered by the previous
survey. * In fact , new images have been discovered in
the inaccessible corners of the painting. In tandem with the reduction of
the megilp around the black lines, these were coated with a temporary protective
layer of isinglass. Further tests will be undertaken at a later date to
determine a method to reduce the megilp over these black lines.
3.3
Tests to remove overpaint from the soffit Early in the month a series of small tests were undertaken to remove the
thick brown overpaint on the soffit. Three solvent mixtures in
thrixotropic gel were tested. The most effective results were obtained using a
commercially available dichloromethane based gel. However, this raised the
issue of stability of the copper based green paint under the overpaint.
Initial research by Dr. Nicholas Eastaugh suggests that there may be a risk of
alteration due to a reaction with chlorinated solvents resulting in a copper
chloride corrosion product (tenorite). Further research is currently being
undertaken into this question and also into alternative paint removal
formulations. The feasibility of leaving the brown insitu is also being
explored.
Dr Nicholas Eastaugh visited the site on 1st
October. During his time on site the data base was upgraded with
information from initial paint samples and a detailed discussion about the
painting. This resulted in further sampling (134-148) to answer specific
questions about the paint structure and technique. In particular we are
looking at the soluble black lines, brown surface layers, a pink/grey
preparatory layer, indentifying other areas of Gee's intervention, and other
aspects of the original paint technique and subsequent
interventions.
4.1 Results from
samples (130-133) collected in September
A fine black layer found over an island of calcium sulphate (130) was probably
part of the restoration applied by local artist, David Gee in 1831. We
still do not understand the origin of the calcium sulphate (but there appear to
be widespread islands) as we had expected residues of calcium carbonate (limewash).
The irregular brown residue particularly visible on the pale flesh areas after
cleaning (131), was initially found to be part of the megilp layer, and was
possibly caused by localized irregularity in the preparation and application of
the coating. However, further investigation of this is planned, including
GC-MS.
A red lac lake was identified as part of the composition for Christ's crimson
robe (132). Interestingly, a comparable sample was taken from Rubens
"Massacre of the Innocents".
A potential complication
of the cleaning was the identification of a pale orange colored glaze (133)
covering the dark green background and the "mille fiores"
decoration. Fortunately this has been found to be resistant to the
cleaning methodology we are using.
4.2 Swab
tests
A sequential collection of swabs were taken from five specific areas to
determine whether there was a pick-up of pigment during the procedure to remove
the megilp. These were sent for analysis.
Tobit Curteis (Tobit Curteis & Associates) and
Rob Hayes (Colebrooke Consulting Ltd.) who are involved with the environmental
monitoring of the painting visited the site. A wireless system for
recording ambient temperature and relative humidity as well as surface
temperature and the measurement of i.r and u.v light levels was installed.
Information can be downloaded via a modem connected to the telephone line.
This will build upon the data provided by the initial monitoring undertaken by
the Wall Painting Dept of the Courtauld Institute of Art.
There has been good success with the
initial cleaning of the sensitive black lines with the i.r camera and monitor,
which has also revealed figures in the top north corner along the vertical edges
that were not previously visible. A second copy of i.r photographs
previously taken have also been ordered to help with the cleaning.
The cleaning and
stabilization process will continue. Trials for the soffit require further
investigation. We are expecting the results of sampling and from our swab
tests.
*
Grundig electonic camera, Type SN76 and Grundig electronic monitor. We
are grateful to Adrian Buckley and Graeme Barraclough of the English Heritage
Conservation Studio for their assistance with this investigation.
John Burbidge
4 December 2002
Granville & Burbidge, 111
Kingsmead Road, London, SW2 3HZ, Tel/Fax 020 8674 1969
Jenny Granville Dip.Restoration (City & Guilds of London Art School), John
Burbidge Dip.Restoration (Opificio della Pietre Dure, Florence)
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