A Study of the Factors Affecting the Deteioration of Old Paint Media

Abstract

This thesis is concerned with the factors which cause
old paint media to deteriorate over a long period of time.

The first part of study is concerned with the development
of techniques for evaluating the changes occurring
during photo-oxidation and two have been found to be
particularly useful. The first involves a measurement
of the decrease in IR_absorbance of the -CH₂- stretching
vibration at 2930 cm_-1 which correlates with weightloss.
The second monitors the formation of scission product
(dicarboxylic acids).

The second part of the investigation is concerned
with the mechanism of action of some of the common pigments
used in old paint-media. Verdigris (basic copper acetate)
was found to be an effective photo-stabiliser due to the
ability of copper acetate to behave as a regenerative
antioxidant in the paint film. This leads to the formation
of conjugated unsaturation during ageing which is the
reason for the discolouration associated with this pigment.
Vermilion on the other hand is an effective sensitiser
for photo-oxidation due to the formation of hydroperoxides.
The probable intervention of singlet oxygen and hydrogen
peroxide via radical intermediates in this process is
indicated.
Vermilion pigmented paint film is considered to be a
useful monitor of photo-oxidation. It is highly active
in the wavelength range 300-365 nm and it is considered
unlikely that physical screening of incident light over
that already employed in art galleries will achieve significant
additional protection. The study suggests that
chemical protectants may provide a long-term solution to
the problem of paint deterioration.

Date of Award	1979
Original language	English