THE AUSTRALIAN GEMMOLOGIST | Is it Copal or Amber?
Is it Copal or Amber?
A yellow-orange transparent resin specimen measuring 61 x 26 x 20mm and weighing 25.6g was purchased at a gem and mineral show in Perth, Western Australia. No geographic location information was given.
Back in the lab at Gemmology House, the usual gemmological tests for amber and copal determinations were applied and the results showed that:
- the specimen contains two insects, various eye-visible bubble-like inclusions, and has a lightly crazed surface (Figure 1);
- it floats in a salt solution and, by hydrostatic method testing, has an SG of 1.063;
- under long wave ultraviolet (LWUV) light it reacts with a bright chalky blue fluorescence (Figure 2);
- under short wave ultraviolet (SWUV) light it is a dull brownish-green;
- the surface becomes sticky when a small drop of acetone is applied (Figure 3);
- when touched with a hot needle, there is an immediate wisp of smoke (Figure 4a) and the needle pulls up a fine hair-like strand of resin (Figure 4b).
These results indicate the specimen was copal rather than amber.
(Note: the last two destructive tests were carried out with the permission of the owner.)
Figure 1. Copal specimen with eye visible inclusions. The position of the ant is arrowed.
Figure 2. Strong chalky blue-white fluorescence under LWUV.
Figure 3. Sticky spot (arrowed) caused by the application of acetone. Note also the surface crazing.
Figure 4a. Puff of smoke produced with the hot needle test.
Figure 4b. Fine thread of resin pulled by a hot needle.
Under the microscope numerous spherical droplets, mostly with brown-orange coloured surfaces, were observed to occur in trains of single droplets and also in groups within larger vacuoles of various shapes. The authors have not, as yet, matched these inclusions with any described or depicted in the literature (Figures 5, 6 and 7). One insect inclusion was complete (Figure 8) and identified at the Boola Bardip WA Museum as an extant spinose ant of the genus Pheidole, likely to have originated in southeast Asian or Pacific regions. Also included is a leg and partial body of an Orthopteran insect (crickets and katydids; Figure 9).
Identification of types of copal requires complex organic chemical analysis and use of infra-red spectroscopy to identify the source tree (Brown and Kelly, 1987).
Tay et al. (1998) used Raman spectroscopy to characterise various ambers, ambroid, copals and plastic imitations. They found that amber showed prominent bands at 1640cm-1 and 1440cm-1, with 1440cm-1 being the stronger. However, in Madagascan copal these two bands are almost equal and there are additional distinct bands at 742cm-1 and 695cm-1.
In an effort to ascertain the source of the copal, the specimen was sent to Tay Thye Sun, at the Far East Gem Lab in Singapore for FTIR spectroscopy and was confirmed as copal with strong peaks around 888cm-1. The test specimen was also compared with copal from Madagascar with Raman results indicating that the copal specimen, the subject of this investigation, was not from that source (Tay, pers. comm., 2024).
Copal is a semi-fossilized and relatively young resin derived from a variety of plants, many still in existence, and is transformed into amber by polymerisation indicated by the intensity of the 1640cm-1 and 1440cm-1 bands. There is a continuum between the original resin exuded by the tree, to then forming copal and eventually amber, as over time and burial, cross linkages occur between the chains of organic molecules.
There are many commercially available sources of copal worldwide, such as those from Africa including Zanzibar, Malagasy Republic, Zaire and Sierra Leone; from Asia in the Philippines, Indonesia, and Borneo; from South America in Colombia and Brazil; and from New Zealand.
The name copal is a word of Spanish origin from the Mexican ‘copalli’ meaning incense and it has been used as such from ancient times (i.e. frankincense and myrrh of biblical note). In the 19th Century to today, an important commercial use of copal resin is in the manufacture of varnish products. From the early 20th Century it has been used as an amber imitation.
Comparison with other copal materials of known location may shed light on the geographic source of the purchased specimen. At the moment, we can probably rule out the Americas (based on the ant) and Madagascar (based on the spectroscopy). Perhaps it has come from southeast Asia? Our colleagues in Singapore are interested in carrying out further research to compare copal from different geographic locations using Raman and FTIR spectroscopy, and we hope to provide further information in a future issue of The Australian Gemmologist, which will assist in confirming copal identification and the geographic source.
Figure 5. Clear droplets and variously shaped orange-brown groups of droplets within vacuoles, beneath the crazed surface. Field of view: 7mm.
Figure 6. Close up of leaf-shaped group of droplets, measuring 3mm including the ‘tail’.
Figure 7. Lines of droplets indicating a flow structure. Field of view: 9mm.
Figure 8. Ant with spiny thorax, genus Pheidole. Measured size: 2mm.
Figure 9. Leg(s) and part body of katydid or cricket. Measured leg: 3.5mm. Photo courtesy of Tay Thye Sun.
Acknowledgements
Thank you to Tay Thye Sun, Far East Gem Laboratory, for facilitating the FTIR and Raman spectroscopy which confirmed the copal identification and an offer of further research comparing different copals.
Thank you to Dr Konstantin Iakoubovskii, Department of Physics, National University of Singapore for kindly carrying out the Raman spectroscopy.
Thank you to Associate Professor Dr Koh Hwee Ling and Mr Eng Chun Heng, Pharmacy Department, National University of Singapore for providing the FTIR data.
References
The Australian Gemmologist, 16(7), pp.263-266.
Tay, T., Shen, Z., Yee, S., 1998. On the identification of amber and its imitations using Raman spectroscopy–preliminary results. The Australian Gemmologist, 20(3), pp.114-123.
Images courtesy of the authors unless otherwise stated.