Simulants Of Amber

by Manisha G

There has been confusion since early days between fossil resins and those of more recent date. To the former category being Ambers from the Baltic, Sicily, Burma, Romania and some of those from the Dominican Republic, while the latter cover the resins and gums kown as copal, dammar and kauri. The former are millions of years old, while the latter may be formed even today.

a) COPAL

copal-stoneCopal is the name for a large group of resins obtained from living trees and also sometimes found in a fossilized condition.

The word copal possibly stems from the Sanskrit and means ‘moon juice’. Copal in Shakespear’s Hindustani Dictonary, is rendered chandra ras – a corruption of the Sanskrit. The Sanskrit compound chandrarasa, or moon juice, also appears linked to the resin sandarac.

Among the various kinds of East African copals some are from Zanzibar. The hardest form of copal produced by a species Of Trachylobium. This part of Africa was formerly German East Africa so the association with copal and amber in trade is a natural one.

Copals are also produced, either historically or currently, from Tanzania, Mozambique and Madagascar in East Africa, along the west coast intermittently from Sierra Leone to Angola, and centrally in Niger and Zaire. The variety of trees producing copals covers Guibourita copallifera in Sierra Leone, Cyanothyrsus in Ghana and Niger as well as various species of Deniellia, and colophospermum in Zaira and Angola. The trees naturally occuring are according to cli­mate; these trees are not cultivated species planted by man.

Resins from South America are also included in the general term copal, the most famous being Demrara anima – Columbian and Brazilian copal. Many of the Central and

South American copals show botanical affinities to Hymenaea, especially the extent species to Hymenaea courbaril.

Historically, by far the most important source of copal was from the island of Zanzibar, now part of Tanzania. Copal was and is found in two distinct conditions : recent, called chakazi or sandarusiza (corrupted by the traders to jack as copal), and ripe or fossil copal.

The raw copal found at the foot of the trees, or tapped from it, did not reach Europe in commerce, but went instead to India and China where it was used for coarse varnish. The ripe or hardened copal was found at a depth of 0.9- 12m, not in association with the parent tree. This resin was cleaned of its goose-flesh white skin, and then shipped to Hamburg in Germany and to British ports. Sometimes copal also reached Britain via Bombay, and these shipments may have included the jack as copal.

Copal diggings arc conducted by the natives in a care­less and desultory manner and the whole trade is surrounded with difficulties. The supply is considered inexhaustible. The amount annually exported is subject to great fluctuations which equally affect the marked value. It is found in pieces ranging from the sizes of small pebbles, upto masses of several ounces in weight.

lCopals have occasionally been used instead of true ambers for ornamental purposes. The copal used seems invariably to have been of a clear golden colour, often with insects as inclusions.

Carvings, and indeed beads made of copal rather than fossil amber, age differently so they are not too difficult to tell apart. Copal is still volatile and the essential oils will soften when they come into contact with ether. A drop of this substance left on the surface for a minute will partially dissolve the resin, and pressure by a finger tip will leave an impression on the softened area. Copal thus treated, or even vigorously rubbed will emit a strong aroma whereas any such aromatic perfume from a true fossil resin would be immediately suspect. Contrary to general belief, working amber does not fill the room with pungent smells of pine trees. The smell is distinctive and much more subtle.

The crazing on the surface of copal rather than amber is also different. Copal crazes in tiny, shallow white areas, the undersurface of the resin crumbling off like dandruff. The crazing on amber is not usually two dimensional, i.e. the cracks go directly into the piece, and do not then turn at 90° causing the surface to flake. The instability of the surface of copal carvings is a real problem when it comes to con­servation. For this reason the Chinese used to lacquer their best resin carvings.

Old copal necklaces again often exhibit this different form of crazing, leaving the surface dull. Any syrup-coloured, clear resin with this dried-up surface should be tested with ether immediately. Sadly, many examples of insect or plant in­clusions in resin old Victorian collections turn out to be of recent specimens caught in copal.

Occasi6nally, copal has been blended with amber chips. This is not very satisfactory as the result is like an ancient version of polybern – the outlines of the harder resin still being visible within the whole. It should also be pointed out that copal will react to fast modern drills and other machinery. It breaks up completely. When drilling copal or recent resins, one can be left with a series of strings of softened matter flying away from the drill like spun sugar threads.

b)  DAMMAR

dammar Dammar is obtained from a variety of different species of resins in Malaysia and the Pacific Islands, but principally from Dammara orientalis, now renamed Aquathis Dammara. Resins like Manila copal are softer than the African copals and make inferior varnish.

The tree grows, for example, on high mountain ridges of the Molucca Islands. It can attain a great height and girth but the timber is inferior. The resin is soft, transparent and dries in a few days, when it turns white with a crystalline appearance.

If often flows spontaneously from the tree in such quantity that it hangs in masses like icicles beneath the ruptures. In­cisions are made, especially in the knots of the tree, and resin is taken directly from the incisions. It is used in Asia for domestic purposes and, although it is used as a varnish, it has a tendency to turn viscous.

c)  KAURI GUM

Kauri-gumKauri Gum is a recent resin. It is the exudation from various trees especially from New Zealand. It is a variety of copal from the Kauri pine (Agathis Australia) hence the term “Kauri gum”. It is also affected by ether.

 

 

d)  PLASTICS

plasticBakelite, a phenol formaldehyde resin, is probably the most important imitation of amber. This material has a greater SG than amber, averaging 1.26, so that such imitations will sink in a solution of salt in water whereas amber will float in it. The refractive index is also higher, averaging 1.66. Bakelite imitations of amber are, in general, inert under ultra­violet rays of X-rays; if there is any glow at all it is usually a brown fluorescence quite unlike that given by true amber.

Celluloid is also be used as an amber imitation. This material has a refractive index of 1.50 and an SG about 1.38. Celluloid shows a yellowish-white fluorescence under ultra­violet rays and X-rays.

Casein, the hardened milk plastic, does not appear to be used very much as an amber imitation despite the fact that material of clear amber colour can be produced. The material seems to be met with in the cruder ‘filled’ form as cheap beads. Casein may be identified by the SG and re­fractive index, 1.33 and 1.55 respectively. Under both long­wave and short-wave ultra-violet light the material fluoresces with a white glow, but, unlike celluloid, casein is inert under X-rays. If a drop of nitric acid is placed on an inconspicuous surface a bright yellow spot is left. This is conclusive, but the effect may be masked by the body colour.

Urea-formaldehyde resin, the amino-plastic, can make a passable imitation of amber, but as yet does not appear to be used. The SG of this plastic is about 1.50 and the refractive index is usually greater than 1.55, generally near to 1.60. Perspex, the polymethyl methacrylate resin, is another plastic which has great possibilities as an amber imitation. It is easily recognized by its characteristics SG of 1.18.

Polystyrene is used as a medium for the production of fancy costume jewellery owing to its ready flow in injection moulding techniques. The SG of this material is 1.05 just lower than for most amber, refractive index is about 1.50. There is a vast number of polymerized organic compounds now made for the plastic industry, many of which, suitable coloured, could supply an amber imitation, but those mentioned are. the most likely.

Two recent amber imitations of German origin are ‘polybern’, which consists of small pieces of real amber in coloured polyester resin; and ‘bernat’, a plastic which has a similar refractive index to amber but the higher SG of about 1.23. This type of imitations are sometimes sold with pieces of plants and insects embedded in it.

Rhinoceros hide (skin) is very thick (20-30 mm) and when polished can be very much amber-like in appearance. It can be turbid and milky, and is sometimes almost completely transparent. It is easily distinguished by its elastic nature and the vein canals.

e)  GLASS

glassGlass imitations of amber have a much higher SG and are cold to touch, whereas amber feels warm. The hardness of glass is greater. A large number of yellow glasses are coloured by uranium oxide and hence show a brilliant yellow- green fluorescence under the ultra-violet lamp. Other glasses not containing uranium may contain manganese and this gives a dull greenish glow which is entirely different from the glows shown by amber under the ultra-violet lamps.

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