Plastic Amber Imitation in a Rosary
Dubai Central Laboratory (DCL) receives almost all types of ambers, natural and treated (e.g. heated, dyed, reconstructed) as well as amber imitations for identification. Amber rosaries (prayer beads) are increasingly popular in Middle East countries, especially the United Arab Emirates and Arabian Gulf countries.
Recently DCL received a rosary for amber identification. The yellow and yellowish brown color, structure, and size of the 102 beads were identical (figure 1, left). At first glance, even with a well-trained eye, this rosary could easily be misidentified as exclusively natural amber. Testing revealed that the rosary was strung with 71 heat-treated amber beads and 31 Bakelite plastic beads.
Spot refractive indices (RIs) of the amber beads were 1.53; observation between crossed polarization of most beads revealed anomalous double refraction with strained colors. Stress spangles and brown thread-like substances are the most noticeable inclusions in these beads; these features are commonly seen in heat-treated amber. The spot RIs of the plastic beads were around 1.64. Aggregate and anomalous double refraction reaction was observed under the polariscope and gas bubbles and swirl marks were the main inclusions.
The most interesting aspect of the specimen was its reaction under long-wave UV. The amber showed moderate to strong chalky greenish blue and yellow fluorescence, but the plastic appeared brown (figure 1, right).This reaction was very useful for differentiating between the two materials.
To confirm the identity of each material, we analyzed their infrared spectra with attenuated total reflectance (ATR) mode (figure 2). Spectrum A displayed main peaks at 1716.4 and 1161.1 cm–1, consistent with amber. The main peaks of Spectrum B were at 1650.8, 1600.7, and 1218.8 cm–1. After comparison with spectrum A and the spectra of other plastics, spectrum B confirmed the spot RI’s identification of this sample as Bakelite plastic.
This rosary is an excellent example of the importance of testing and disclosure, because even an experienced person could not differentiate between the amber and Bakelite beads with the unaided eye.
