©J. Paul Getty Trust
Causey, Faya. The Properties of Amber, Ancient Carved Ambers in the J. Paul Getty Museum
Ed. Faya Causey. Los Angeles: Getty P, 2012. museumcatalogues.getty.edu. Web. 18 February 2019.
The Properties of Amber
Amber is a light material, with a specific gravity ranging from 1.04 to 1.10, only slightly heavier than that of water (1.00). Amber may be transparent or cloudy, depending on the presence and number of air bubbles (figure 13). It frequently contains large numbers of microscopic air bubbles, allowing it to float and to be easily carried by rivers or the sea. White opaque Baltic amber may contain as many as 900,000 minuscule air bubbles per square millimeter and floats in fresh water. Clear Baltic amber sinks in fresh water but is buoyant in saltwater. Baltic amber has some distinguishing characteristics rarely found in other types of amber: it commonly contains tiny hairs that probably came from the male flowers of oak trees, and tiny pyrite crystals often fill cracks and inclusions. Another feature found in Baltic amber is the white coating partly surrounding some insect inclusions, formed from liquids that escaped from the decaying insects.
Amber’s hardness varies from 2 to 3 on the Mohs scale (talc is 1 and diamond 10). This relative softness means that amber is easily worked. It has a melting-point range of 200 to 380°C, but it tends to burn rather than melt. Amber is amorphous in structure and, if broken, can produce a conchoidal, or shell-like, fracture. It is a poor conductor and thus feels warm to the touch in the cold, and cool in the heat. When friction is applied, amber becomes negatively charged and attracts lightweight particles such as pieces of straw, fluff, or dried leaves. Its ability to produce static electricity has fascinated observers from earliest times. Amber’s magnetic property gave rise to the word electricity: amber (Greek, elektron) was used in the earliest experiments on electricity. Amber’s natural properties inspired myth and legend and dictated its usage.
In antiquity, before the development of colorless clear glass, a complex technique perfected in the Hellenistic period, the clear materials known were natural ones: water and some other liquids; ice; boiled honey and some oils; rock crystal; some precious stones; and amber. Transparent amber is a natural magnifier, and, when formed into a regularly curved surface and given a high polish, it can act as a lens. A clear piece of amber with a convex surface can concentrate the sun’s rays. One ancient source suggests that such polished ambers were used as burning lenses.
Once cleaned of its outer layers and exposed to air, amber’s appearance—its color, degree of transparency, and surface texture—eventually will change. As a result of the action of oxygen upon the organic material, amber will darken: a clear piece will become yellow; a honey-colored piece will become red, orange-red, or red-brown, and the surface progressively will become more opaque (figure 14). Oxidation commences quite quickly and starts at the surface, which is why some amber may appear opaque or dark on its surface and translucent at breaks or when subjected to transmitted light. However, the progress of oxidation is variable and depends on the time of exposure and other factors, such as the amount and duration of exposure to light. In archaeologically recovered amber, the state of the material is dependent upon burial conditions, and the degree of oxidation can vary widely, as the Getty collection reveals. The breakdown of the cortex causes cracking, fissuring, flaking, chipping, and, eventually, fractures. Only a very few ancient pieces retain something of their original appearance, in each case because of the oxygen-free environments in which they were buried. For instance, two fifth-century B.C. female head-pendants that were excavated at waterlogged Spina are remarkable for their clear, pale yellow color (figure 15). A large group of seventh-century B.C. amber-embellished objects from the cemeteries of Podere Lippi and Moroni-Semprini in Verucchio (Romagna) were preserved along with other perishable objects by the stable anaerobic conditions of the Verucchio tombs, which had been sealed with a mixture of water and clay (figure 16). Various colors and degrees of transparency are in evidence, from pale, clear yellow to clear orange or red to opaque yellows, oranges, reds, and tans. Inclusions are common.
Many pre-Roman figured ambers exploit the material’s transparency, offering the possibility of reading through the composition: the back is visible from the front and vice versa, albeit blurrily. This is a remarkable artistic conception, iconographically powerful and magical. Two extraordinary examples are the Getty Lion (figure 55) and the British Museum Satyr and Maenad (figure 17). From its top, the underside of the lion can be discerned. In the multigroup composition of the London amber, the large snake on the reverse appears to join in reveling with the figures on the front.
A number of seventh-century Greek, Etruscan, and Campanian objects include amber set into precious-metal mounts or backed with silver or gold foil. Some are internally lit by foil (or possibly tin) tubes. Amber’s glow, its brilliance and shine, would be immeasurably enhanced in this way. Simply shaped amber pieces set into gold and silver are mirrorlike, emanating radiance and banishing darkness. Amber faces once mounted on polished metal, the Getty Heads of a Female Divinity or Sphinx (figures 18 and 45) might even seem to issue light, like the principal astral bodies, or to capture the shimmer of light on water.
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The Properties of Amber