Koussoulou, T.; (2008) An evaluation of photodegradation inhibitors in the conservation of naturally dyed historic silks. Doctoral thesis , University of London.

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Abstract

Photodegradation of naturally dyed historic silks is a problem that confronts many museums. It continues as long as the objects are displayed, as both ultraviolet and visible light are capable of causing degradation. Degradation may be seen in the fading of the dyes and in the loss of textile strength. Five photodegradation inhibitors were tested on silk dyed with natural red dyes and dye combinations in order to evaluate their ability to increase the light fastness. The selected additives belong to the classes of UV absorbers and antioxidants, and combinations of those were also tested in order to investigate a possible synergetic effect. The preparation of sampling material was based on original silk samples taken from Greek museums and identified in detail using scanning electron microscopy (SEM), energy dispersive X-ray analysis and high performance liquid chromatography. Evaluation was focused on the colour induced changes after artificial ageing of the treated samples and also on the tensile strength, the application methods, and the prospective reversibility of the additives. Exposure to electromagnetic radiation was performed with British Standard method BS1006:1990 using blue wool standards, by gradually covering the samples in order to investigate the fading rates over specified time periods, with an increase of temperature to 50 C and in three different relative humidity levels of 30%RH, 50%RH and 80%RH keeping stable temperature at 35 C. Colourimetric measurements were used for the evaluation of colour changes using the system of the Commission International de l'Eclairage (CIE). Comprehensive SEM investigation was performed on the inhibitor-treated samples. Benzophenone and hindered amine types showed promising results on individual samples, but an inhibitor combination of an ultraviolet absorber and an antioxidant showed good performance over a wide range of dyes and dye combinations. Synergism was confirmed in two inhibitor combinations which improved light fastness at all three humidity levels, with the best performance shown at the lowest humidity. In every case, the inhibitors proved more effective on the more light stable dyes such as madder and cochineal, while less photoprotection was given to the more sensitive dyestuffs such as brazilwood and safflower. Consideration was also given to the ethics of using photodegradation inhibitors in historic textiles. The research has shown that the use of the selected photodegradation inhibitors is not recommended on historic silks according to the present conservation requirements and codes of practice.

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