Conservation Science

Textiles 79

original use of the ‘dynamite’ weighting process. The red weft threads proved to
be just lightly tin weighted, while the red warp threads and blue silk threads
were devoid of inorganic weighting. It seems reasonable to ascribe the friable
nature of the cream-white silk to either direct or indirect consequences of the
original tin weighting process.

4.4 Assessing the Condition of Silk by Microanalytical Techniques

It was clear from the outset that the majority of the ensign silk had suffered sig-
nificant deterioration and was mechanically weak and brittle. In other cir-
cumstances, more detailed studies which will define the physical and chemical
state of better-preserved materials, are of value in informing conservation deci-
sions. Practical and ethical considerations dictate the application of analytical
methods which require only minute specimens consisting of no more than a few
fibres a millimetre or two in length. Spectroscopic, X-ray diffraction and mass
spectrometric techniques, which can report on changes at the microstructural
and molecular levels, are the subject of promising current research. Viscometric
and chromatographic procedures which reveal the relative fibroin polymer
chain length are already routine. The most useful methods will show unique
signatures for degraded material that correlate with the physical properties of
the aged threads. For example, we have investigated a variety of silks by high
performance size exclusion chromatography and demonstrated a simple rela-
tionship between the strength of the silk and the fibroin peak retention time,
which relates to the polymer molecular weight (Figure 17).

0 20 40 60 80 100 120 140 160 180

3. 50

retention ti

me,

t/ R

min

3 .00

2. 50

2.00

1. 50

1.00

0. 50

0.00

breaking load / g

Figure 17The breaking load of a variety of silk samples plotted against their retention time,
tR, in high performance size-exclusion chromatography