The identification of synthetic organic red pigments in historical plastics: Developing an in situ analytical protocol based on Raman microscopy

The identification of colorants in historic plastics is a methodological and analytical challenge. Although deformulation is performed by the plastics industry, in the case of historical objects, sampling is often impossible, and in situ protocols are needed. The accurate identification of colorants provides insights into historical plastic formulations, supports planning of conservation studies, and critical data for objects that already exhibit color change (e.g. fading). Indeed, colorants may degrade following exposure to light, and color changes have been reported for plastic objects. The analysis of colorants remains a challenge, and microsampling is usually required. Successful identification of red pigments from thirty historical plastics is reported following a new in situ analytical protocol based on Raman microscopy. Information about other pigments, fillers and plastic polymers are reported. Fading has been observed in the historical plastic objects containing Pigment Red 53.