A background to amber

A BACKGROUND TO AMBER

WHAT IS AMBER?

Amber is extremely old, solidified tree resin.

Resin should not be confused with sap, which is a nutrient-bearing liquid that rises through the plant to feed it. All plants contain sap, but not all trees produce resin. A few do so in response to damage – for example broken branches or insect infestation – by exuding a sticky liquid and covering the damaged area. Some trees produce so much resin that it pours down the tree, inside or outside the bark, and collects around the roots at the base.

With time some resins disintegrate, but others harden and become solid. They become covered by debris and buried. The hardening process continues, and during those stages they can be called ‘copal’. Further hardening and maturing over a long period of time and in the right geological circumstances can turn some copals into amber.

Baltic amber jewellery

Plant resins contain acids, alcohols and oils, sometimes collectively known as ‘volatiles’. As the resin solidifies the volatiles evaporate, and the material becomes polymerized -- that is, the molecules that make up the resin link to form long chains. As it matures further, these long chains cross-link and the material becomes harder and more stable. Finally the material becomes completely inert and undergoes no further chemical or physical changes. It is then termed ‘amber’. These processes can take millions of years to complete. They are a continuum, and it is impossible to say that copal becomes amber at any given age.

Kauri trees in New Zealand, and detail of resin running down bark.

Most ambers are not today found where they were actually produced. An example of this is Baltic amber, which was produced in large forests that grew in and around the area that we now call the Baltic Sea, but, thanks to geological shifts, the sea disappeared and the land mass moved north.

Further, resins of the same origin may be deposited in two different geological strata, for example by Ice Age melts, with the result that some matures and becomes amber, and some retains volatiles and so is still copal. This has happened with resins found in Borneo, thought to be about 15 million years old. Those found in sandstone are amber, while those in the clay beds have not ‘matured’ and are still regarded as copal.

Ambers and copals can contain plant and insect inclusions – flora and fauna – which are well preserved in the resin as it has antiseptic and dehydrating properties, and hermetically seals the inclusion, creating a time capsule. Much can be learnt from the inclusions in amber, and it is often through them that the age of the resin can be determined. Bark from the host tree or plant debris from the forest floor may also be found in amber.

AMBER VARIETIES

Amber is found world-wide, and has been produced by various trees. It is believed that the Cretaceous ambers derive from Araucaria-like trees, which were conifers. The botanical origin of Baltic amber has long been under discussion. It may derive from a tree of the Pinus succinifera genera, but it also seems likely that it could derive from the genera Pseudolarix, the modern relatives of which produce resin with a very high succinic acid content.

The chemical composition of amber is (very approximately) carbon 80%, hydrogen 10% and oxygen 10%. These percentages vary slightly, and all ambers contain other trace elements. Baltic amber has sometimes been called succinite, because it contains a sigificant percentage of succinic acid (3 – 8%) compared to other ambers, which contain none, or very little.

Amber is found in varying quantities across the globe. By far the biggest deposits are those around the Baltic, where the resin is mechanically extracted from open pits. Baltic amber accounts for more than 98% of the amber sold today, and most of it has undergone some form of treatment before it reaches jewellers’ shops. The treatments vary from completely re-constituting the resin to simply darkening the surface. (See ‘The Enhancements and Treatments of Baltic Amber’.)

Baltic amber is considered to be from 34 to 38 million years old, and occurs in colours ranging from creamy-white opaque (caused by sub-microscopic bubbles inside the material), through clear golden, to almost black. A single piece will often display a variety of colours and opacities. It does not fluoresce in daylight. Over one thousand species of flora and fauna have been found in Baltic amber, most commonly termites or ants. Unique to Baltic amber is the appearance of white matter surrounding part of an insect. This is not mould, but is a chemical reaction caused by the insect decaying in the resin.

Baltic amber beads, and unpolished 'rough', both showing typical colours and opacities of Baltic amber

Amber from the Dominican Republic is reckoned to be between 16 and 20 million years old. It tends to be of a deep golden, clear colour, sometimes displaying a red tinge which is caused by natural oxidation or geological process. It often contains large quantities of debris, and can also contain beautifully preserved flora and fauna. It is mined by hand from shafts dug into the hillsides. Dominican amber can fluoresce green and blue – a phenomenon that is more visible when the material contains a large amount of dark coloured plant debris. Attempts at treating Dominican amber have failed as it tends to liquefy.

Typical amber beads from the Dominican Republic, and 'rough' fluorescing in sunlight.

Mexican amber may be slightly older, at about 16 to 20 million years. It is also mined by hand and is never treated. It is found in the Chiapas region of Mexico. It occurs in various colours ranging from clear, pale gold to deep cognac. The red, polished, Mexican amber on the market gets its colour as a result of natural surface oxidation. The resin has been carefully polished to remove the rough surface and leave a thin skin of darkened material. Mexican amber can fluoresce in daylight in the same way as Dominican amber, though the darker material tends not to fluoresce.

While some of the material is completely clear and even in colour, quite a lot of it contains debris. This often appears in parallel stripes, and is typical of Mexican amber. The material contains fewer insect inclusions than Dominican amber.

Mexican amber: polished pieces and slices showing typical parallel lines of inclusions.

‘Burmite’ from Myanmar (Burma), is the only Cretaceous amber used for gem purposes. It is now known to be over 100 million years old. It occurs in colours ranging from golden through red to brown, or golden with red swirls. It is the only amber that can have a truly ‘red’ body colour (rather than a red colour caused by oxidation), which has made it much sought-after and copied. A variety of burmite is opaque with swirls of coffee and cream colours, and looks a little like wood. Called ‘root amber’, the type is very rarely seen in other ambers.

Burmite is mined intermittently, largely depending upon the political situation in Myanmar. It is found in the hills around the Hukawng Valley in Kachin State, and is dug out of the hillsides by hand. It is never treated.

Burmite is a little harder than other ambers and is often cracked, with calcite inclusions. It can contain flora and fauna, though these tend to be less well preserved than in other ambers. It can also contain large amounts of debris, with the result that the material looks completely black. If such a piece is seen in daylight, however, it looks blue due to fluorescence, indeed Burmite is known for its strong fluorescence. (See also ‘A Closer Look at Burmite – amber from Myanmar’.)

'Burmite' cabachon in incandescent light, and the same in UV light.

The relatively young amber from Sarawak in Borneo is not seen much on the market. It is usually a dark brown colour and clear. It is not treated, and is sometimes carved.

There are several ambers that are of historic interest. The Cretaceous ambers from, for example, North America, France and the Lebanon can tell us much about the world several million years ago, but are of little or no value as gem organic material. Tertiary ambers from Romania (Rumanite), and Sicily (Simetite), have been worked as gem material, but are so rare today that examples are seldom encountered outside museums or private collections. Cretaceous amber from Japan has similarly been worked, but again is only found in museums. Occasionally a new find of resin occurs and there is much accompanying excitement, which usually dwindles as it is realised that the resin of no particular significance or use.

A few years ago amber was found in the far north of Australia. Research is still ongoing, but it is thought to be a relatively young amber, probably about 12 million years old. It is not as durable as for example Baltic amber. It occurs in a variety of very attractive transparent colours from palest yellow to almost red, and also in dark, opaque shades.

A more recent find is amber from Ethiopia. It is not very ‘mature’ yet is thought to be very old. Research is ongoing. The colours vary from the usual transparent amber colours, to green. The green variety strongly resembles the treated Colombian copals, and is the subject of much discussion as to its veracity. If it is a natural green colour it must have been altered by geological processes, the effects of which are similar to our modern autoclave treatments.

COPAL VARIETIES

Copals are found world-wide. Their ages vary from a few hundred to a few million years old. They are softer than amber, but their hardness increases with their maturity. The following are some of the better-known examples of copal.

The best known is so-called ‘kauri gum’ from New Zealand. It varies greatly in age, some being well on the way to becoming true amber. It derives from the Agathis australis tree, a few examples of which can still be seen growing in the North Island of New Zealand today. It is more stable than most copals and can be carved. It contains very few insect inclusions.

Kauri gum tends to be a slightly darker golden colour than other copals, all of which have variations of sherry colours – mostly of the pale, dry sherry variety.

The East African and Madagascan copals come from the legume Hymenaea. They are thought to be about 10,000 years old and can be rich in insect inclusions.

Colombian copal can similarly be inclusion-rich. Its age is unknown. It is sometimes treated to resemble amber, and is the basis for the ‘green amber’ currently found on the market. It is often incorrectly termed amber, possibly to encourage sales. It can occasionally display a slight hint of pink.

Copal from the Dominican Republic can contain beautiful examples of flora and fauna. It is often sold as amber. Its age is unclear, but is thought to vary considerably.

Left: Colombian copal, and right: flower head in Dominican copal (greatly magnified).

AMBER FAKES

Amber is one of the most commonly faked organic gems, and possibly one of the easiest to copy. It has little or no crystalline structure, no visible and definite structural characteristics, it can be clear, opaque, various colours, and can contain air bubbles. Further it is light and warm to the touch. Plastic is therefore the obvious material to use when copying it.

Amber has, however, been copied for hundreds of years – since long before the advent of plastics. One of the earliest attempts consisted of stuffing pig or cow gut with egg white and boiling it. The resulting material was dried for a long period and could be cut and dyed.

In between natural amber and the total fakes are all the re-constituted, pressed materials, which are made of amber chips or amber dust, possibly dyed, and often sold as natural amber. (See ‘The Enhancements and Treatments of Baltic Amber’.) It is the opinion of Organic Gems that such material should be sold with full declaration of the processes used, but it is acknowledged that much of it is sold as natural amber.

Some of the early pressed amber – commonly known as ‘ambroid’ -- can be distinguished from natural material because of the pattern of swirls of colour, which tend to be elongated or feathered. Amber mixed with plastic may have the same pattern. This is caused by the production method used (extrusion). Other tell-tale signs of imitations may be marks left from moulding, or total evenness of colour. (See ‘The Enhancements and Treatments of Baltic Amber’ for further details and photographs. See also 'Early Plastics as Imitations of Organics'.)

The hard-boiled egg white variety of amber stimulant might be easy to spot, but the plastic fakes and amber mixtures or pressed ambers of today can be incredibly difficult to tell from the natural, untreated resin, or that which has received acceptable treatments. Treated copals react in the same way as amber to most of the tests used, and can only be tested with absolute certainty in a laboratory.

There are many examples of amber fakes or treated amber on the market today which leave the customer puzzled and uncertain. Probably the best advice, therefore, is to buy only from a reputable and trusted dealer -- or, when that is not possible, never to spend more than one can afford to lose if the material turns out to be an imitation.

Left: plastic bead showing swirls of colour, and right:

amber bead floating in saturated salt water, while

plastic bead has sunk to the bottom.

TESTING AMBER

Amber becomes positively charged when rubbed against a rough surface, so that it can pick up a light object such as a feather. However pressed amber, copals, and some plastics react in the same way, so this is not a good test.

The following are simple tests used by gemmologists:

Salt Water: Almost all plastics sink in saturated salt water. ambers and copals float. Results may be altered by air in bead drill holes, or thread. Not suitable for mounted items.
*Hot Point: The material is touched with a red-hot sharp metal point, and the ease with which it enters the material is noted. Young resins melt at a lower temperature and allow the point to enter the material easily. This test also gives the Burning Aroma. (Care should be exercised as some early plastic imitations are made of celluloid, which is highly inflammable.)
*Solvent: A solvent such as acetone or ether is dropped onto the surface of the material. This may have to be repeated several times. Young resins turn sticky. (Prolonged immersion in solvent may crack mature amber.)
*Sectility: A sharp knife is used to scrape a small sliver of material, e.g. from the drill hole of a bead. Plastics tend to pare while amber splinters.
The test that is most conclusive, though not infallible, is an FTIR photospectrometry reading, which must be done in a specialised laboratory.
Fluorescence: Freshly cut or polished amber has a stronger fluorescence under ultra violet (UV) light. This is especially true of Baltic amber, which displays chalky blue fluorescence under pure UV light when fresh, turning to a dull ochre with time. It does not fluoresce in daylight. Treated, re-constituted and pressed ambers show little fluorescence under pure UV light and none in daylight. Plastics are inert unless they contain an additive specifically designed to fluoresce.

*NB: These tests are destructive and can leave a mark.

Detail of fungus gnat in Baltic amber, greatly magnified.