The Dangers to Silk Resulting from Environmental Pollution
Natural silk is an animal-derived fibre obtained from the cocoons of the Domesticated Silkmoth or the Chinese Tussah Moth. The silk fibres are made of proteins – fibroin and sericin. The treatment process for raw silk entailed boiling the cocoons in hot water; after disentangling the threads were boiled in a soap solution and also subjected to various metal salts to give them the desired softness and shine. During the dyeing process the fibres were treated with further chemical compounds.
The factors which cause the destruction of silk include light – above all ultraviolet radiation – increased or decreased humidity, raised temperature, micro-organisms, fungi, and pollution of the natural environment. Silk fibres’ high sensitivity to light is a consequence of the fact that the proteins which make up the fibres are subject to the process of photo-oxidation, and this process may be accelerated in the presence of certain chemical compounds which were introduced into the fibres during dyeing.
Air pollution – nitrogen oxides, sulphur oxides and ozone – also play a great role in the degradation of silk textiles. Under the influence of moisture, nitrogen and sulphur oxides become acids, while ozone is a strongly oxidising compound. Humidity which is too low and too high a temperature may cause denaturation of the proteins forming the fibres, while too high a humidity is conducive to the development of moulds and fungi.
Understanding the processes of silk damage is crucial to the development of a method for preserving silk textiles safely.