Colorimetric and spectral properties of woolen yarns dyed by different types of Madder

Due to the wide application of madder (Rubia tinctorum) for dyeing the Persian carpets and also diversity of this natural dye, in this study different types of madder were collected and analyzed. Madders were collected from Mediterranean region, and different parts of Iran including Yazd, Kerman, Bafgh, Khour va Biabanak, Naein, and Ardakan. As a first step, after preparing a clear solution from different samples of madder in water, their absorption spectra in the range of 190 to 1100 nm were obtained and compared with each other. Then a specific type of carpet yarn was dyed during the same process of indentation and dyeing using each of the discussed species. By measuring the reflection of the dyed samples in the visible range, their reflectance spectra were determined and compared. Moreover, the calorimetric characteristics of all dyed samples were calculated and reported under D65 optical standard and 1964 standard observer. As a result, it is shown that colorimetric specification of sample dyed with Mediterranean madder is different from other samples. Also using the well-known Kubelka-Munk function, the K/S values were calculated from measured spectral reflectance of all dyed samples. Additionally, the Principal Component Analysis (PCA) was implemented to determine eigen values, eigen vectors and dimensional sizes of the spectral reflectance. Then the spectral reflectance of all dyed samples was reconstructed by employing different number of principal components. Finally, the RMS and Delta E error between actual and recovered reflectance were calculated and reported