Some of the popular names used for describing varieties of amber, such as pure, dirty, frothy, nude, or jacketed do not refer directly to either its colour or degree of translucency, but to the origins of the given variety. Pure amber derives from pure resin which was uncontaminated by any other substances. Contaminants in the form of tiny dispersed fragments of plant matter are responsible for the variety known as dirty amber. Fossil resin which contains minute inclusions of rotten wood or splinters of fresh tree tissue becomes pale brown, brown or even black in colour. In frothy amber the purity of the amber, and hence its degree of translucency, is affected by turbidity introduced by the presence of tiny air bubbles. This aerated structure resembles foam and produces semi-translucent and opaque varieties of amber.
The fashion for clear amber, which is rarer in nature than its opaque counterpart, has given rise to ever greater improvements in the techniques used for clarifying it on an industrial scale. Nevertheless, amber in its natural state remains the most highly valued. Nothing compares to the unique varieties of blue and dappled amber. The artificially induced cracks known as ‘spangles’ will never take the place of so-called pseudo-inclusions, which occur when internal weathering takes place within a piece of amber along the edges of a cavity left behind by a wood splinter, nor can they replace the ‘drawings’ created by dispersed plant matter.
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Amber found on the Sambian Peninsula has lain for at least 40 million years, from the moment of its deposition in blue earth, in conditions which are very favourable to its conservation (primarily not changing moisture). As a result, it has remained in its primary varieties of pale yellow and white, which are often thought to be less appealing. The amber which can be recovered from Quaternary sediments in Poland has the same origin as that found on the Sambian Peninsula, however, during the last one million years it has been redeposited many times and laid down in ever younger sediments. This sequence of events has clearly added to its aesthetic appeal, making it the most highly rated of all fossil resins used as gemstones. Jewelery manufacturers nowadays often strive to recreate these naturally acquired characteristics through artificial means, sadly stripping the amber of its inherent beauty. Resin which builds up in stalactite forms is usually clear due to the way in which its volatile components (of which there are up to 20% in fresh resin!) evaporate. If these components do not trigger the creation of a porous (foamy) structure, then the resultant amber will retain a beautiful translucency. Where, however, bubbles of gas are generated very quickly, e.g. on the surface of the resin directly affected by exposure to sunlight, or where the release of these gas bubbles is inhibited by surface hardening or because the resin is trapped inside a crevice, the resin will begin to ‘foam’ and become opaque yellow or white. There are several varieties of white amber, from pure white chalky amber to the off-white variety known as osseous or bone amber. Their internal structures differ in terms of the number, size and density of air bubbles trapped inside. The smaller the bubbles and the more densely packed together they are (the greater their number), the whiter the amber will be.