Textiles 85
DATUS EST NOBIS’ (The Father is noble and so is the Son) in Gothic letter-
ing, at the centre of which are Mary, Joseph and the infant Jesus in the stable,
along with Sts Catherine and Barbara. Like the frontal, the warps are linen, with
wool the predominant component in the weft, alongside silk and metal threads.
The tapestry was decorated with a silk fringe and metal thread braid edging,
though investigations revealed that this latter adornment was a later addition, as
it contained brass filaments manufactured by a method not developed until the
18th century. Although they are both of a similar period and origin, it is believed
that the superfrontal was not originally intended as a companion piece for the
frontal, but that the two were paired at some time after their manufacture.
When it was received for conservation, the tapestry was soiled in places
with a light grey dust, as well as fibre dust along the lower edge of the under-
side, and there was some staining around the Virgin and Child. Pink deposits
were observed on the St Lucas roundel and waxy deposits near the scroll of
Ahaziah. Some of the exposed linen warps were discoloured to brown; many
of the wefts have faded. There were holed areas where both the linen warps
and wool wefts had deteriorated; the beige-coloured wool appeared to be in
particularly poor condition, and was largely absent. Many of the metal threads
exhibited signs of corrosion. Evidence of previous repairs was found, in the
form of small linen patches used to reinforce weakened areas, and coarse
stitching around some of the figures.
5.1 The Chemical Composition and Microstructure of Wool
Wools and other similar mammalian hairs are largely composed of keratin pro-
teins. However, unlike the other natural proteinaceous fibre, silk, wool is cel-
lular in nature: the fibres consist of relatively hard, flattened, overlapping
cuticle cells, which surround the central cortical cells; in some fibres, these
may in turn surround a hollow medulla (Figure 23).
The cuticle can vary in thickness between one cell, for the finest wools, up to
several dozen. These cells contain amorphous keratin arranged in layers, with
the resistant exocuticle overlying the inner endocuticle. The resilience of the
exocuticle derives in large part from its sulfur-rich (cysteine) nature, which
allows the formation of the disulfide bridges that reinforce the polymer; the
endocuticle has much lower sulfur content and so is more susceptible to deteri-
oration. The exposed surface of the cells is covered by a protein membrane,
the epicuticle, along with waxes and fatty acids, which impart a further degree
of chemical and mechanical resistance. It is the overlapping cuticle cells that
give wool fibres their characteristic scaly appearance (Figure 24). Lying between
the cuticle and the cortex is a continuous band of intercellular materials, which,
in combination with the two adjacent cell walls, lends a resistance to penetra-
tion by water and other chemicals.