Amber imitations - Copal

Gabriela Gierlowska

GALERIA ZDJĘĆ Click to enlarge

Copal is the fossilised natural resin of both deciduous and coniferous trees which occurs in nature in a great number of varieties, mainly in tropical but also in subtropical (New Zealand) regions; or: copal is the partially transformed (subfossil) natural tree resin. “ There is an ongoing discussion in scientific literature [...], about what should be called copal, and what qualifies as a fossil resin. Age is a frequently used criterion and there are those who favour the limiting of copal age to between 10 thousand and 5 million years ” (Barbara Kosmowska–Ceranowicz).

These natural, comparatively young subfossil resins are often described with their geographical specification, sometimes with a reference to their mother tree. The best known ones are: copal from Zanzibar , copal from Madagascar , Kauri copal, copal from Manila , Japanese copal, Colombian copal and copal from the state of Sabah in Borneo.

Copal as an imitation of Baltic amber
Copal is found in lumps of diverse shapes, sizes and colours, and in varying degrees of transparency. It is obtained from the surface of the earth or from its layers near the surface . Sometimes, it can contain inclusions. Sometimes, raw copal can have a rough surface, with so-called goose bumps. Its fracture is usually glassy, generally lightly coloured but there are cases of intensely coloured copal nuggets, from yellow to brown. Copal dissolves partially in alcohol, acetone, ether, chloroform and benzene. It dissolves fully in solvent mixtures. Kauri copal dissolves in alcohol with acetone, alcohol with turpentine while Manila copal - in acetone with turpentine. Some oils (flaxseed, rosemary oil) soften copal.

Copal melts at ca. 110÷180ºC (copal from Zanzibar even at over 300ºC). Physical properties: hardness 1.5 to 2.5 (Mohs scale); density 1.0 to 1.19 g/cm 3 ; refractive index 1.54; greasy sheen; ice-lemon-yellow and yellow-brown colour. Copal's age can be determined with C14-dating. Copal is used mainly as an ingredient in lacquer, sealing wax and varnish.

Copal occurring locally in various parts of the world was used to make ornaments, necklaces and figurines. Imported to Europe , it also served as surrogate material for Baltic amber (succinite) in jewellery products. In 1891, H. Beck developed a method of hardening natural resins, surrogates for copal and amber. “The resins are mixed with equal parts of mixes of ethyl alcohol, glycerine, phenyl and carbohydrates, with the addition of metal oxides” (British Patent No. 9747), and in 1911, F . Spiller developed a method of processing copal into an amber-like material. “The method consisted in removing the bark from the copal, softening it with carbon disulphide and then by heating it evenly in hermetically sealed casts under pressure ” (German Patent 247734).

However, in spite of their being pressed, hardened and varnished, amber imitations made of copal were easy to tell from genuine amber. It was enough to rub a piece made of copal with cotton wool soaked in ether to get a matt smudge where the surface layer dissolved. Also when a heated needle touched copal, it drew thin threads behind it, which stuck to it. Within a certain period of time (as short as a few years), copal products would get covered with long hairline cracks from the surface down.

The use of copal in jewellery
Today, technical and technological progress have substantially transformed copal and discovered new possibilities of its use in jewellery. In the copal hardening process, every piece is wrapped in aluminium foil of paper, then hardened in stages in an autoclave by increasing the temperature, pressure and heating time, which initially are 150 ° C, 10 at and 12 hours, respectively; and 200-210 ° C, 20-25 at, 20 hours, respectively, in the final stage.

The hardened copal lumps are made transparent by placing so-called water settlers in the autoclave; hardening without the water settlers produces opaque lumps. The currently fashionable green colour is obtained by adding water at each stage of the copal hardening process in an autoclave in an amount relative to the size of the autoclave without fitting water settlers. After the copal has been hardened in such a way, the foil is removed and the copal is cut to produce the desired shape (pendant, ball, cabochon), then it is mixed with talcum and heated again in the autoclave. After this treatment, the products are cut and polished, usually in vibrators.

Several rounds of thermal treatment in an autoclave leads to the copal's gradual hardening. It becomes comparable to amber in terms of hardness and processing viability, while the gemstones made of it are deceptively similar to amber. Hardened copal can also be dyed and sparkles can be introduced.

The producing of sparkles in copal is also a process which takes several stages: ready stones are heated for 12 hours in an autoclave at 200-210 ° C and a pressure of 45-75 at; then after the gas is removed from the autoclave, its contents are cooled with ventilators. In the final stage, water with vinegar is added. Sparkles are produced with the use of water settlers.

Colouring, where copal products are treated to assume the colours of amber, golden or cognac, usually takes place on pallets in a steriliser. It starts at a heating temperature of 100-120 ° C for 12 hours and ends at a temperature of 160-180 ° C and a time appropriate to obtain the desired tint. New possibilities for obtaining excellent amber imitations which are difficult to identify are provided by pressing copal with amber and various additives: dyes and fragrances.

Identification
Today, ether is no longer enough to identify copal. An experienced expert may be able to recognise it by its smell, after treating a copal products with a heated needle. A smell which is different from that of amber will definitely be sensed by an amber jeweller while working on copal. However, FTIR Spectroscopy (spectral curve) identification is fail-safe and reliable. The curve obtained in this way is a kind of “fingerprint” of the substance.