Series editors' preface - Wood Tools

dimensional forms such as curved components
or carving. Decisions about the type and extent
of retouching should be made on a case by
case basis with a clear aim in mind.
Reconstruction may be partial or complete and
incorporate or exclude fills, colour and imitating
texture or craquelure. The decision to
undertake non-mimetic retouching may allow
the object to be presented in a variety of ways.
It may allow, for example, a conjectural reinterpretation
whilst retaining the viewer’s ability
to distinguish original from non-original work.
Some conservators have favoured replicating
the original structure and pigments in their
reconstruction of losses. This approach may be
adopted in the hope that the retouching will
match the original more closely, and that as the
retouching ages any divergence from the
appearance of the original will be minimized.
Even though original pigments and layer structure
may be faithfully reproduced, however, it
is impossible to replicate the original method of
application or ageing. Other conservators have
favoured approaching retouching as a colour
matching problem, believing that the use of
original pigments is not essential to match the
repair to the original. In both cases, retouching
is a step by step process, built up in thin layers.
Each layer of pigment or glaze applied during
colour matching will have some effect on
the final result. Replicating the original structure
can impart a degree of optical complexity to a
retouch, as light penetrating the layers can
replicate the look of an aged paint more accurately
than a simple structure, which may
appear flat in comparison.
General ethical principles relating to retouching
include documenting original condition and
the extent of retouching. Retouching should be
restricted to areas of loss. In the past, restorers
have often extended retouching past the area of
damage in order to blend it in with the original.
Ideally, retouching undertaken as part of a conservation
treatment should not obscure original
material or decoration on an object. Artist’s
quality sable brushes can be used to ensure
accuracy. It is widely accepted that retouching
materials should be distinguishable and safely
removable from the original (Perry, 2000).
Light, colour and metamerism
Light can be defined as the range of electromagnetic
radiation to which our eyes are sensi-
Principles of consolidation, aesthetic reintegration and coatings 579
tive. Colour perception is not an absolute but
relies on an interaction between a light source,
an object and the eye of an observer. This interaction
must be reproduced if colour perception
is to remain constant.
Colour matching requires a strong diffuse
light source. When light strikes a coloured
object, individual wavelengths may be transmitted,
reflected or absorbed. Different light
sources contain differing proportions of
coloured light (Figure 12.5). The proportion of
each wavelength available to be transmitted,
reflected or absorbed will vary with the light
source and, in combination with the spectral
reflectance of the surface, will change the
colour perceived by an observer (Figure 12.6).
Ideally the colour temperature and colour rendering
quality of light used to retouch should
match that used to display the object. Since an
exact match for each object is rarely achievable,
a good light source for colour matching is generally
considered to be natural light from a
large north-facing window (south-facing in the
southern hemisphere) due to the significant
proportion of blue light. Artificial light sources
that approximate natural light include colour
matching lamps, colour-corrected halogen
lights or a mixture of normal incandescent
bulbs and fluorescent light sources. Although a
good light source is essential for retouching,
matching colour is only part of the process. It
is possible, for example, to resolve a degree of
loss with the ‘wrong’ colour. Thomson (1988)
discusses the effect of colour temperature and
colour rendering in the museum environment.
For a thorough discussion of colour see
McLaren (1983); for information on light see
Brill (1980).
Metamerism is a term used in colour science
to describe the effect when two colours that
match each other under one light source differ
when viewed under a second light source of a
different colour temperature (see Figure 12.6).
Metamerism will not occur if pigment identical
to the original is used. In many cases, however,
this is not possible and a modern substitute
must be used. For example, although Prussian
blue may be colour-matched using cobalt blue,
French ultramarine or cerulean blue, the result
will prove metameric because these three modern
pigments have a high reflectance of red in
comparison with Prussian blue (Staniforth,
1985). It may be helpful to try to match the