CHARACTERIZATION OF SILK-COTTON AND WOOL-COTTON BLENDS PATTERN BOOKS BY FIBER OPTICS REFLECTANCE SPECTROSCOPY. THE BOOMING MARKET OF FIRST SYNTHETIC TEXTILE DYES IN EARLY 20th CENTURY

A remarkable number of early 20th century azo synthetic textile dyes was characterized by Fiber Optics Reflectance Spectroscopy (FORS). Items are part of silk-cotton and wool-cotton blends pattern books of Leopold Cassella & Co., a leading firm at that time. Focusing on early dyes from this privileged point of view, meant for us providing our own scientific contribution to restore luster to a historical period that represented the keystone from upmarket natural dyes to synthetic ones on a large scale. A selection of spectra on silk-cotton blend with the same dye concentration was compared color by color. In the case of wool-cotton blend textiles, two concentrations were available for each dye. Therefore, spectra comparisons between the same dyes used in silk-cotton and wool-cotton blends were carried out, as well as between the same dyes in different concentration in the case of wool-cotton textiles, simulating possible fading conditions. In addition, almost each analyzed dye was linked to its molecular structure. Finally, the obtained set of data has been statistically treated. The complete dataset was subjected to an exploratory analysis using PCA that exhibited an organization of the samples based on brightness and colors. The generation and validation of a PLS-DA model confirmed the recognizability of the samples based on color and pointed out the excellent conservation conditions implemented. The method provides a non-invasive, fast and low-cost approach for the recognition of azo dyes, based on the combined application of FORS, colorimetric parameters and chemometrics and lays the foundation for a reference database.