Series editors' preface - Wood Tools

The principles outlined above for supporting
tears may be applied to loose areas and lifting
edges. Losses may be infilled using parchment
matched to the colour, texture and surface
treatment of the original. The patch should be
supported using the technique described
above. In some cases it may be appropriate to
laminate new parchment for full support,
though this should be undertaken by an experienced
specialist.
Coatings
Any coating which is applied to previously
untreated parchment will change its appearance,
texture and patina and there is, therefore,
a general presumption against such treatments.
Where parchment has been varnished in the
past there may be areas where the substrate
parchment is exposed. In such cases, the application
of a coating runs the risk of differential
take-up between varnished and unvarnished
areas.
16.4.3 Shagreen
In furniture conservation, the term shagreen
usually refers to the skins of sharks and rays.
The term shagreen is derived from an entirely
different material, sometimes known as ‘shagreen
leather’, derived from the back of a
horse or donkey and embossed with seeds.
The historical derivation of the term can cause
some confusion and it is important to identify
which material is actually present on an object.
The physical characteristic that produces the
decorative effect on ray skins is the presence
of cartillagenous nodules in the grain surface
of the skin. These nodules are hard and the
skins have been used as an abrasive material
in the past. The skin itself could be processed
and abraded to reveal the small white circular
pattern which is characteristic of this material
and produced a hard wearing and decorative
surface. Gopfrich (1999) describes the history
and conservation of shagreen leather, specifically
an untanned hide that had been
embossed with seeds.
The skin of other aquatic animals such as
chat (Squalus catalus) and dogfish have also
been used and are often also called shagreen.
Kite (forthcoming) mentions the use of
untanned shagreen to bind European ceremonial
sword hilts and its incorporation into the
Conserving other materials II 739
handles of Samurai swords and dirks during
the Edo period in Japan (1615–1868). When
used in this way the surface of the shagreen
was not abraded, as the nodules on the skin
provided additional grip.
Shagreen was used in Europe, from the seventeenth
century onwards, as a decorative covering
material for boxes and was also utilized
in instrument cases and jewellery (Willemsen,
1997). The French cabinetmaker Ruhlman often
used shagreen to great decorative effect and
this material enjoyed a period of popularity in
England in the 1920s when it was favoured by
the Duke of Windsor (Springer, 1984).
Both tanned and untanned shagreen may be
encountered as a decorative surface. Although
tanning raises the shrinkage temperature of
leather, in many cases the shagreen used on
articles of furniture was untanned. Although
dry heat is usually tolerated, it may be helpful
to establish the shrinkage temperature before
undertaking a conservation treatment that utilizes
heat, e.g. heat setting of adhesives. The
sudden contraction of the skin at the shrinkage
temperature usually requires both heat and
moisture, but it is possible, for example if
aqueous adhesives have been used, or in conditions
of high ambient RH, or if the shagreen
has been humidified and has not yet returned
to equilibrium with the ambient environment,
for contraction to occur without additional
moisture.
Shrinkage temperature may be established
by taking a small sample, which is thoroughly
soaked in cold water overnight. The temperature
of the water is then raised, ideally at 2 °C
per minute, and the temperature at which the
sample suddenly and irreversibly shrinks is
noted. Microscopic examination using a heated
stage may allow the use of a very small sample
and has been described by Young (1990)
and Larsen et al. (1993). If taking a sample to
establish shrinkage temperature is impracticable
it should be assumed that untanned shagreen
has been used.
The shrinkage temperature of fish collagen is
significantly lower than that of mammalian collagen
(c.65 °C). Generally speaking, the shrinkage
temperature of cold water species is
around 38–45 °C, whilst that of warm water
species is around 50–56 °C. Shrinkage temperature
has a direct relationship with the hydroxyproline
content of the collagen – low