74 Chapter 4
When it was received for conservation at the Textile Conservation Centre, it
was in an extremely weak state, especially the areas of cream-white silk
where significant sections of the fabric were missing and where there was
some discolouration. There was extensive staining, principally from water
and oil, as well as rust marks around the nail holes.
Again, an understanding of the chemistry and structure of the component
fibres and their condition should inform the choices made for conservation
treatment, display and storage. So, we continue this case study with such a
description, before alluding to some of the original processing protocols, which
could affect the silk fibres’ stability. The condition of silk can be gauged at the
microstructural and molecular level by contemporary analytical methods and
we illustrate this, prior to discussing the details of silk deterioration. The par-
ticular rationale of our research is to inform conservation practice and we
complete this section by referring to the specific treatment carried out on the
ensign in light of its apparent condition.
4.1 The Chemical Composition and Microstructure of Silk
Silks are produced by a number of insect and spider species, but the major
source of commercial textile silks are the silk moths of the family Bombyci-
dae, of which the most important is the domesticated silkworm, Bombyx mori.
The first known references to the culture of silkworms (sericulture) come from
China in the second or third millennium BC, from where it spread through Asia,
then on to the Middle East and eventually Europe.
Moth larvae produce the polymeric material from a liquid crystalline phase
to form a protective cocoon; silk is extruded from the spinneret as a ‘bave’,
consisting of two roughly triangular fibroin filaments (‘brins’), about 20m
across, bound together by a second protein, sericin (Figure 13). In commer-
cial production, the chrysalid is killed before it can hatch (which would dam-
age the thread), and a continuous filament can then be unreeled from each
cocoon, giving typically 500–800 m of useable thread.
Fibroin SericinFigure 13Cross-sections of silk fibres: (a) cartoon of a native silk fibre and (b) scanning
electron micrograph of a fractured, processed textile fibre (10m across)