Amber usually occurs in colours ranging from golden to brown, and most of it is opaque though it can contain debris from the floor of the original forest where it was formed. A very small amount of natural red amber is also found, but this comes from a couple of sources only. (See ‘Red Ambers’.) Natural green amber has for a long time been a myth, and the only green amber that existed was that which fluoresced in UV (ultra violet) light. No green amber was thought to exist naturally, and all the ‘green amber’ that was available was the result of some form of treatment. Very recently green material has come to light in Ethiopia. It is said to be natural, and if so it has formed under natural geological conditions that we today manage inadvertently to copy in order to turn golden resins green. The material is still being investigated in various laboratories around the world.
Amber from the Dominican Republic, left: fluorescing green in sunlight;
the smaller piece viewed by transmitted light.
THE OLD TREATMENT METHOD
For many years we have been able to buy ‘green’ Baltic amber. The amber is not itself green, and the colour is an illusion. It is caused by backing transparent golden material with something black: plastic, paint, or simply burning the amber to make the reverse surface black. If yellow and black colours are mixed, the result is a dark green – this is what is happening when the amber is seen from above. From the side it remains golden. The material is usually clarified and heated to produce ‘sun spangles’ before the black backing is applied. This treatment is still widely used and the resulting material is very popular. It is only used on Baltic amber. (See ‘Baltic Amber Treatments’)
Left to right: clarified, heated and burnt Baltic amber seen from top; seen from back; seen from side.
THE NEW TREATMENT METHOD
In recent years a new form of ‘green amber’ has appeared on the market. It is mostly transparent and is the result of a series of treatments in an autoclave (a heat/pressure machine that has long been used to turn opaque Baltic amber transparent). The length of time in the machine, the pressure used and the temperature at which it is run varies according to which resin is being treated, and is a closely guarded secret. There is also a gas present in the treatment, most probably nitrogen. The material resulting from this method looks green from all angles, and when cut in half it is seen that the material is green throughout.
Unpolished material with
typical brown areas
Polished, treated Colombian copal
showing colour range.
Extensive research has been carried out on the material as gemmologists were generally rather sceptical that it was possible to turn amber green, even though it has long been accepted that resins could be altered in an autoclave to turn them transparent or to darken them. The research proved, however, that it was true. Not all resins can be induced to change colour, for example Baltic amber can be turned green, yet Japanese amber cannot. The easiest materials to alter were the less mature resins. i.e. copals. (See ‘A Background to Amber’) The resulting material can vary from pale to strong green, and may be blotchy in colour and retain areas of brown.
Baltic amber treated to turn green, and the same piece
7 years later.
There is some Baltic amber on the market that has been treated in this way, but the vast majority of the material we see is derived from immature resin, Colombian copal, which is aged about 200 – 300 years old. The finished Colombian material has been artificially hardened and matured by the process. Tests carried out on the surface of the material give results similar to that of amber. (The treated material is more stable, with a higher melting point and its surface does not become sticky when moistened with solvents, as does the surface of untreated copal.) We do not, of course, know what the long-term stability of the young material will be – even if it has been artificially matured. We do know that the green colour can fade slightly with time.
THE NEW METHOD EXTENDED
Because the resins do not always turn a good green through and through, and also because not all the manufacturers are equally adept at producing the green material, a new variation appeared on the market. It is a more vibrant green – more blue-green than young grass green. In some lights it seems to have a slightly bluish sheen.
Left: coated and treated Colombian copal (top) and uncoated (bottom), and right: smashed bead showing green colour throughout.
Testing of this material by cutting it to examine the interior showed that it is green all the way through. Tests by UV visual (a laboratory test) prove that there is a dye coating the surface enhance the colour, or to mask a poor colour.
Laboratory tests turned up one confusing detail. Although with most of the treated resins it was possible to tell by laboratory tests (FTIR spectra) which of the resins was the starting material, it is not always possible with the green material. Some confusion can therefore remain about whether a string of green beads started out as, for example, Colombian copal or Dominican amber. Because of this it has been impossible to agree a name for the new material. Most, but not all of it is treated copal (a material which, in its untreated form, is generally regarded as inferior to amber as it is less mature and durable), so dealers selling treated ambers have good reason not to wish that their wares to be labelled as copal.
Treatments of resins should always be disclosed at point of sale, but unfortunately this is not always done and the green treated copal is sometimes sold as ‘Natural green Caribbean amber’, or the Baltic material as ‘rare green Baltic amber’. The material being sold as green amber is attractive in its own right. Because of the lengthy processes involved (which are not always successful), it is not cheap.
There are examples to be found of other forms of ‘green amber’, though these are less common. One is where a resin has simply been coated in dye, without bothering to autoclave it first. Another form is re-constituting the resin by grinding it to a powder and adding green dye prior to re-forming it. This type tends to be more obvious and unnatural in appearance. Further possibilities are copies made from glass or plastic. These last are mostly encountered online in popular auction sites of dubious origin.
Totally reconstituted Baltic amber
with a green dye added to the mixture.
NATURAL GREEN AMBERS
A few golden ambers can appear green when viewed under ultra violet-rich light, e.g. sunlight, and fluoresce. Examples of this are some ambers from the Dominican Republic, and also some from Mexico. This is a natural phenomenon but the colour is dependent upon the light upon the surface and does not penetrate the amber. The illusion of the amber being green is stronger if the material is viewed against a dark background. (See photos at the top of this article.)
The recently discovered material from Ethiopia is still extremely rare and until we have more information from laboratory testing it is unlikely to become more than a curiosity. One huge drawback for the material is that is resembles so closely autoclave-treated Colombian copal to look at. Some contains insect inclusions, which would have been incinerated in copal treated when in an autoclave.
©2018 Maggie Campbell Pedersen. All rights reserved.