Non-invasive identification of historical textiles and leather by means of external reflection FTIR spectroscopy

Identifying the fibres in historical textiles presents a complex challenge due to the wide variety of plant, animal and early synthetic materials that have been used. Traditionally, this identification process involves sampling followed by either microscopic examination or ATR-FTIR spectroscopy. However, there are instances when sampling is restricted due to the good condition or significant value of the object under analysis. Additionally, the presence of leather components alongside textiles can further complicate the identification. This paper proposes a novel non-invasive method for fibre identification based on External Reflection (ER) FTIR spectroscopy, which has been rarely applied to textiles or leather. The current research demonstrates that ER-FTIR spectrum is a viable tool for fibre identification on both recent and historical textiles. The non-invasiveness of the analytical approach enables a comprehensive investigation without compromising the number or position of samples. Respect to ATR-FTIR spectra, the ER-FTIR spectra frequently exhibit an amplification of certain diagnostic bands, facilitating the identification of the various fibres examined in this study (cotton, hemp, viscose, silk, wool, leather, polyamide, acrylic, polyester). The extended spectral range (7500-375 cm^-1) which is provided by ER-FTIR spectrometry also contains extra bands in the near infrared region, which can provide key information for the discrimination due to the lack of distortion phenomena. The technique was applied to the characterisation of textile materials coming from a collection of 10 traditional Japanese samurai armours spanning from the 16th to the 20th century (Museo delle Culture, Lugano, Switzerland). For the first time, the results provided a comprehensive overview of the textiles utilized in Japanese armours across various historical periods. Overall, the appearance of materials in samurai armours reflects the evolution of armour-making techniques and the influence of socio-cultural factors throughout Japanese history. Synthetic and semi-synthetic materials were easily detected, revealing the occurrence of a past conservation treatment or the early adoption of modern man-made materials in the manufacturing of traditional armours. The approach outlined in this case study can be applied to textile collections of various kinds, offering a reliable mean to discern the yarn composition and detect non-original components. The method also appears as a valuable prescreening tool for designing a less intrusive yet more informative sampling strategy, should additional details about fibre type and dyeing be necessary.