Abstract:
Research in painting conservation needs accurate, efficient and non-destructive methods
to determine the rate of composite decomposing actions without disturbing the painting.
Decomposing results in a change of visual characteristics that can be directly measured.
In this study, attention was focused on assessing whether the measurements of such
characteristics identify the rate of decomposition to an acceptable accuracy. Samples that
simulate the traditional Sri Lankan rock and wall paintings, made by several techniques,
were used for the study. Two categories of painting samples were considered, namely the
samples with clay ground and organic paint and samples with lime based ground and
mineral paint. These were subjected to destructive interventions in order to accelerate the
decomposing processes and generate defects within a short period of time. Continuous
heating up to 60 C, alternative cooling and heating, introducing moisture at a rate of 3 mL
per 24 hours per sample, introducing 0.1 M NaCl and MgSO4 solutions and inducing
mechanical stresses at 100 Pa and 1000 Pa for clay and lime based samples are among
the destructive interventions used. Four (04) indirect parameters were used to measure the
rate of decomposing of samples. Testing in the wind tunnel and the actions of moisture,
temperature and illumination were these parameters. One sample of a painting was kept in
open air and another one was subjected to testing. Measurement of the changes in color
and visual defects tested the rate of decomposition. The Mach and Reynolds numbers used
in the wind tunnel testing were 1.25 and 5x106. The amount of moisture, temperature and
illumination used for the purpose were 5 mL, 30 C and 200 lx respectively. The Pearson
product-moment correlation coefficients for variations measured were 0.86 and 0.94
respectively and the results proved the existence of a relationship between the parameters.
Keywords: Rock and wall paintings, decomposition, painting conservation
Acknowledgement: Ford Foundation, USA (Research Grant No. 920-0756)
