Bleaching of historical old linen fabrics: the case of the Shroud of Turin

In ancient times, cultural heritage linen clothes could undergo a bleaching process, which differs from the modern bleaching processes that appeared after the late 18 th century. This study introduces a simple, non-destructive method to detect whether linen was bleached. It describes several techniques assumed to be ancient and analyzes their differences from modern procedures, using the Fourier Transform Infrared (FTIR) spectrum in the 1500–1700 cm −1 band. Raw and bleached samples from seven different origins were studied. The use of modern and ancient processes was analyzed by their FTIR spectra. As a result, slight changes were observed between the spectra of raw and bleached samples in the indicated band. An original simulation of the treatment with natron produces a noticeable peak at about 1740 cm −1 . Finally, the trends observed allow comparison with the specific case of the spectrum of the Shroud of Turin.