Andrew Hirst - 26th February 2003
1. INTRODUCTION
January saw the return to site of the conservation team after the Christmas
break. Work to the wall painting progressed as before, though now without the
aid of the infra red camera and monitor. The IR photographs we already had,
together with our investigations using the infra red camera and monitor in the
months leading up to Christmas were agreed to have provided sufficient information
for us to continue the work.
There were further changes to the team of conservators: Sophie Godfraind left at Christmas to pursue her PhD and two new additions, Alexandra Gent and Catherine Nunn, both easel painting restorers, joined the team, each on a part time basis.
2. TREATMENT
The methodology of the treatment did not change and has continued as outlined
in previous reports.
This month the emphasis has been placed more on joining vertically the cleaned sections on each level of scaffolding. This required taking up the first scaffolding board nearest the wall painting in order to allow access for cleaning and stabilisation.
3. SCIENTIFIC SUPPORT
Dr. Nicholas Eastaugh examined the 8 paint samples collected on 12.12.02 and
both John Burbidge and Eva Gascón Pinedo attended his laboratory for
two days to review the results of all the analysis undertaken to date and the
use of the database at this mid-point of the programme. These samples and their
visit were designed to help answer some of the outstanding questions about the
wall painting; its original technique, materials and the evidence for previous
attempts at restoration. Despite taking specific samples to answer specific
questions, some of the results remain inconclusive. However, many of these samples
have contributed towards developing a much clearer idea about the intervention
by Gee in 1831.
3.1 Results from samples 163 to 169 and 158 (retaken) collected in December
Sample 165 was taken to better understand the nature of the blue drapery of
an apostle. Analysis revealed that the dark blue effect was created by a thin
layer of indigo (provisionally identified by polarizing light microscopy) on
top of a bright green layer. The presence of indigo has been confirmed elsewhere
in the painting using Raman microscopy.
The red lake pigment and evidence of a black underdrawing was found to be common
to numerous samples. The red lake glaze from the "old blood" (the
darker of the two colours of blood) from the chest of Christ (167) was comparable
with a similar glaze over Christ's halo (166). Horizontal fractures in the red
lake layer of sample 167 cannot be explained and may indicate potential problems
of future delamination.
Sample 168 from the robe of an apostle revealed a thin green overpaint layer which had all the characteristics of an intervention by Gee (fine, uniform particle size and shape). The paint structure was also very similar to the overpaint on a demon sampled previously (155)
Sample 169 was taken from an area of dark brown residue megilp, after initial cleaning. This residue was much more resistant to the regular cleaning technique than the majority of the megilp coating. Prior to a second phase of cleaning it was considered important to understand what this residual material was. This would also help to explain its existence and resistance to cleaning. The sample was submitted for Gas Chromatography Mass Spectrometry (GCMS) analysis in order to answer the first question definitively. Preliminary GC-MS results indicate a drying oil, probably linseed oil. Additionally, compounds identified by the search-match program as squalene are probably one or both of two related compounds known to occur in triterpenoid resins, in this case probably indicating mastic resin. This would seem to suggest that the megilp residue is in fact the residue of two of the components of megilp and that the missing bituminous component has either separated out or been leached from the varnish (possibly as a reaction to sunlight). Alternatively, the megilp was not thoroughly mixed when initially applied.
Sample 158 (retaken) from the arm of an apostle showed all the characteristics that the red/brown glaze was applied by Gee.
4. ENVIRONMENTAL MONITORING
The wall painting's exposure to light (principally UV and IR wavelengths) and
to fluctuating levels of relative humidity (RH) and temperature have been a
concern throughout the conservation project. Months ago RH and temperature monitors
were installed near and on the surface of the painting and the accumulated results
downloaded onto a computer system. Another monitor measuring UV and IR light
levels was also installed some time ago. Unfortunately this monitor was not
downloading the data successfully due to a software problem. The software problem
has been identified now and steps have been taken to get this part of the environmental
monitoring system working properly.
5. PRIMARY OBSERVATIONS
The majority of the wall painting is now consolidated and exposed. We have also
accumulated a considerable amount of technical information. It is therefore
an appropriate time to consider the technical and ethical questions involved
in the second stage of cleaning. We are also trying to establish how much of
the wall painting is original and how much is the result of one or more previous
restorations. We have evidence supporting the 19th century Gee intervention,
but we are also looking very closely to see if there is evidence for an earlier
intervention. This assessment takes into account any anomalies in painting technique
or layer structure noted with the naked eye on the wall painting, and the results
of microscopic/technical analysis of paint samples.
There have been two articles about this wall painting conservation project published to date in the Coventry Telegraph. On the 18th of January an article also appeared in the Birmingham Post. During January a photographer from the Independent newspaper also visited site, raising the possibility that the wall painting may receive some coverage in a national newspaper.
6. PLANS FOR FEBRUARY
The overall reduction of the megilp layer will continue as before. However,
a series of tests will be undertaken to determine the best method for reducing
the discontinuous islands of brownish residue from the surface of the paint.
Further careful consideration will also be given to the question of how best
to approach the work to the soffit.
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)