Identification of pigments in artworks by inverse tangent derivative of spectrum and a new filtering method

Abstract

Nowadays, employing an economical and non-destructive method for identifying pigments utilized in the artworks is vital due to their antiquity value. One of the non-destructive methods for this purpose is spectrophotometry, which is based on the selected absorption of light. Mathematical descriptive methods such as derivatives of the reflectance spectrum, the Kubelka-­Munk function and logarithm are being used to clarify the spectrophotometric data. In the present study, the mentioned mathematical descriptive methods were applied to identify the most common pigments used in Iranian artwork but were not efficient for the samples. Therefore, inverse tangent derivative equation was used on spectral data for the first time and a considerable difference in the profile of reflectance curves was found. In the next part, to have a simpler and more practical method it was suggested to use filters made up of pure pigments. By using these filters and placing them on the samples, imaging was done. Then, images of samples with and without filter were evaluated and pure pigments were distinguished. The mentioned methods were also exerted to identify pigments in a modern Iranian art painting specimen. The results confirmed that these methods provide reliable answers indicating that physical methods (alongside chemical methods) can also be effective in determining the types of pigments.