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Article source: "On the Properties of Amber" Amberif Preview 2008. Pgs 14-16.
On the Properties of Amber
by Prof. Barbara Kosmowska - Ceranowicz
The properties of each mineral or gemstone are its most crucial identifying feature; even in antiquity they posed an intriguing issue also for amber researchers. The feature whicch was recorded earliest, and which is referred to even today, is the attraction of particles of other substances, which caused the Greeks to call amber elektrum. Unfortunately, today we know that also some artificial resins have the same property.
Today, Baltic amber, or succinite, is well known but not yet fully researched, although it can be identified unambiguously. It is difficult to write briefly about it, in order not to miss something.
Georgius AGRICOLA (De natura fossilium, 1546) was the first to obtain amber acid, which has remained one of succinite's identifying features until today. Three amber ingredients are obtained in dry distillation: amber acid in crystalline form, liquid amber oil and solid colophony.
The 3 to 8% amber acid content in succinite belongs to its diagnostic features. Other fossil resins either contain no amber acid at all or 0 to 3% only. Today, when talking about the properties of amber which can identify it ultimately and unequivocally, we need to use the research results obtained by researchers using specialist equipment. As one of more than 100 kinds of fossil resins found in the world, amber is a mixture of macromolecular substances and the products of their oxidation so as such it cannot be represented by one chemical formula. Today, gas chromatography and mass spectrometry (such research has been going on for more than a decade) allows us to determine 60 constituents out of which, in amber, 5 different compounds make u amber acid alone. Each of these compounds can be designated by a separate chemical formula.
Other parameters of succinite:
Elementary composition: C 61-81%, H 8.5-11%, O ca. 15%, S up to 0.5%. Sulphur, as a secondary constituent, may reach a quantity from zero to a few per cent, for instance Ukrainian succinite has up to 5% sulphur, although it does not exceed reference levels in the Baltic region.
Solubility in organic solvents: poor.
Chemical tests on amber are particularly difficult due to its poor solubility. As only the solved fraction can be analyzed, the results of such tests are fragmentary. research using physiochemical equipment and methods has come to our aid today.
Hardness on the Mohs scale is a qualitative experimental value which describes a mineral's ability to scratch the next mineral: 2.0-2.5 (on the Mohs scale: 1-talc, 2-gypsum, 3-calcite...), which means that we can scratch amber with calcite. Let us remember that the harness of amber, and even more so of improved amber, does not determine its resistance, which is yet to be described by any indicator.
Microhardness, which means hardness measured on the basis of the collision effect (tested in a special microscope) between a hard pyramid and the surface of amber, expressed by a numerical index, for amber: 199-290 megapascals (=19.9-29 kg/mm2)
Density: 0.96-1.096 g/cm3
Melting point: 287-300 C; 300-380 C(acc. to other sources)
Softening point: 150-180 C
Refractive index: 1.539 - 1.542
Electrifies negatively
Response to heating: pure resin scent
Response to flame: burns with a smouldering yellow flame
In UV light: blue
Inclusions: gaseous - spherical or oval, organic - fauna and flora
One of the many methods used today to identify succinite is infrared absorption spectroscopy (IRS ). One and a half to two milligrams of amber is enough to perform the test. IRS is the cheapest and primary analytical method for the identification of succinite.
IRS test on fossil resins in 1963-1964 were performed independently in Russia, Germany and the USA. In Poland, they beagn in 1968 and developed further within the Italian-Polish Committee for Amber Route Research Established in 1972. The infrared method for amber testing has been all but abandoned by chemists, given a multitude of other more up-to-date and expensive research methods which, however, are often inaccessible and not always necessary to the amber professional. This topic is very current today in light of the development of the jewellery industry market, raw amber shortage and the ensuing sorry consequences in the form of increasingly frequent imitations. Imitations require quick identification precisely by means of the IRS method, which is te most univocal in distinguishing Baltic amber from other types of fossil resin, copal or artificial resin. The Museum of the Earth at the Polish Academy of Sciences in Warsaw has extensive comparative material in this regard, which will be compiled in an atlas of resin curves obtained using this method, to be published in the coming years.
Amber property researchers are seeking to use their conclusions to develop a classification of fossil resins. Once amber acid was discovered in amber, in the 19th century it became a criterion for dividing fossil resins into a group which contains the acid: the succinite group, and other which either do not contain it at all or only in the quantity of us to 3% the retinite group. Gdansk chemist O. Helm performed a large number of amber acid analyses on samples of various resins to identify Baltic amber, for instance in the items found in Mycenaean tombs. This led to an erroneous conclusion that the presence of amber acid was a simultaneous indication that the amber came from the Baltic Region. This theory had long been a bone of contention; today we know that amber acid indicates the kind of resin, not its geographical origin. Baltic amber is very typically characterized by its varieties and forms of occurrence.
Varieties: diversified internal structure is responsible for the degree of transparency and white colour of amber. Moreover, the diversification of varieties is influenced by the impact of impurities and, secondarily, by the degree of weathering. There is no black variety of succinite.
As described by the author in Bursztynisko magazine, electron microscopy proved useful in the research on amber's internal structure, which above all accounts for its beautiful white variety (so desired in the process of making a gown for the icon of Our Lady of Czestochowa). For the first time it was possible to discover and document, with scanning microphotography, the presence of microcrystals, which after further research turned out to be free amber acid crystals. The crystals "grew" in the bubbles of the porous structure of white opaque Saxon amber (succinite)
The properties of Baltic amber, such as its degree of transparency, extraordinary beauty and richness of its natural colour varieties, made more uniform by amber jewellers through amber improvement methods, have also been the subject of research for many years now. Researchers at the University of Silesia have undertaken testing the organic and inorganic ingredients of the "water" which remains in autoclaves after the amber improvement process. the results of this research allows us to assume that water with salts and organic components is partially responsible for amber's natural opacity.
Form of occurrence: dripstone forms, internal natural casts whose shape reflects the forms of crevices in their mother tree. Without going into their origin, crevices were formed underneath the bark, in the bark, between the annual rings, in the wood of the trunk or root, or as wounds when for instance a tree lost a branch. Natural amber forms depended primarily on where the resin oozed from and what form the crevice in which it gathered had. The surface of crevices is inscribed as diverse impressions on the external surface of amber nuggets.
They also depended on the quantity of the effluent affected by the season of the year, the extent of the wound, sun exposure, the tree's age and state of preservation. A fence plank continues to secrete resin for some time, too.
Even if diverse natural, but never accidental, amber forms developed in a conducive environment, it does not automatically mean that they survived until our times. The history of millions of years of travel or even residence in a deposit created multiple opportunities for the damage or even destruction of specimens. So let us try to retain natural amber forms in jewellery and decorative items as far as it is possible. An amber drop or an icicle formed of many think layers will be not only a work of art in the hands of master amber jewellers but also a work of nature from at least 40 million years ago!
Topics which are very relevant to the development of fossil resin science, concerning fossil resin properties and classification, appear at various even seemingly very monothematic amber science conferences, such as palaeoentomology congresses. Such topics have also been presented for almost 15 years at AMBERIF scientific seminars organized by the International Amber Association, Gdansk, and the Museum of the Earth, PAS, Warsaw (published in: Kosmowska-Ceranowicz B., Gierlowski G. (Ed): Amber - Views Opinions. Scientific Seminars Amberif 1994-2005. International Amber Association, Museum of the Earth PAS, Gdansk International Fair Co. Gdansk-Warszawa 2006; 243 paages).
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