PROPERTIES of AMBER

The name amber relates specifically to fossilised resin which has succinic acid - COOH(CH₂)₂COOH₁₅ present in its chemical makeup. Baltic amber can have succinic acid present between the ranges of 3 to 8 percent. Amber which is clear usually has the lower levels of succinic acid and this increases as the amber becomes more opaque. Fossilised resin which possess no succinic acid is officially classified as retinite.

(Amber is a poor conductor of heat and because of this it always feels warm to the touch).

Hardness

On Moh’s scale of hardness amber has a hardness of 1.5 - 2^.5. This varies according to the origin and type of amber.

*The author has in his possession resin which was taken from the Cotui mine in the Dominican Republic, this is the youngest deposit discovered on the island to date. Some research has indicated that this particular source should be classified as copal and not amber. The hardness of the few pieces the author owns is between 1 and 1.5.

**Some Baltic osseous amber can be as soft as 1 on Moh’s scale.

Optical Qualities

The refractive index of amber is 1.54. The refractive index measures the level to which light is bent as it passes through the material under examination. The refractive index of amber remains fairly constant regardless of its type or geographic origin. The diagram to the right demonstrates the 'bending' of light as it passes through the body of the amber and the angle of refraction. (Amber bends light to the same degree that rock crystal does).

This quality can be exploited when photographing inclusions in amber. Quite often an inclusion will be positioned where the curvature of the amber distorts or impairs the view of the article. By immersing or coating the gem in a fluid with a similar refractive index the distorting refraction can be effectively neutralised. Some of the photographs of inclusions contained within this web site were rendered distortion free using this technique. The fluid used was clear mineral baby oil. The pieces were immediately washed and cleaned after coming into contact with this substance.

Specific Gravity

The specific gravity of amber is relatively low, approximately 1.05 - 1.10. True amber floats in heavily saturated salt water. It will not float in sea water but is easily rolled and moved even in mild sea conditions, provided it is loose. Some frothy amber can have a specific gravity as low as 1.

Structure

Amber does not posses any crystalline structure and has no cleavage. It fractures conchoidaly and will not take a facet easily. It is not always homogenous in nature. Pieces can be found which consist of a series of concentric rings or layers. This reflects the way in which the original resin was laid down in successive layers. Amber of this type is called shelley amber. Where the fossil resin is free of any layers the general term to describe this kind of formation is massive amber.

Amber can be found which has retained the original shape in which it was formed. One of these forms are stalactites. In these cases fresh resin has dripped from a tree branch and gradually set in a stalactite formation. Another form is ‘amber within amber’. That is to say a drop or run of resin which set and has been covered by a later flow of resin. The picture here clearly illustrates this concept. You can see a perfectly formed drop of ancient resin surrounded by a later discharge.

Amber is most frequently found as rough lumps in mines or pits. When the amber is collected from beaches it is usually in the form of rounded pebbles or ‘cobbles’ and can range in size from tiny grains up to larger pieces 40cm across at their broadest part.

Fluorescence

Amber has fluorescent qualities but is often difficult to detect. The oxidised surface of amber can occasionally fluoresce more than the un-oxidised amber beneath though this can be reversed in other samples from the same source. It is the generally experience of the author that amber fluoresces quite poorly despite assertions to the contrary in many published works on amber. Pictures will often be displayed in books which show pieces of amber fluorescing an electric blue, what is often failed to be explained is that the exposure time for these photographs was in excess of 2 minutes. It is for the reader to decide for themselves who is in fact correct.

Colour

The colour of amber could occupy an entire web site to its self. Nearly every book written on amber contains a section or numerous references to the colour of amber. For the most part colour is described in two ways; turbidity and hue.

Turbidity is the extant to which it is clear or cloudy. Usually the more cloudy amber is the nearer to the colour white it becomes. An entire language has grown up to describe the different gradients between white and clear amber, here are just some examples:

A. Chetnik, in his book ‘Pocket Dictionary of Polish Amber Varieties’ names more than 80 varieties and colours of amber so this list can only hope to name some of the more common or frequently used terms.

Often the surface colour of a piece of amber is considerably darker than that of its interior. This is due to the oxidisation of the amber. In this picture one half of a raw piece of Russian amber has been cleaned, the colour difference is obvious.

The turbidity which is the key factor in defining these names given to amber is not the result of any chemical, or the affect of any inclusion trapped in the resin. The turbidity is a result of thousands of tiny air bubbles held in the amber. The size and density of the air bubbles results in different shading. The size of the air bubbles range between 0.00017 mm - 0.02 mm. The smaller air bubbles packed densely together, about 9,000,000 per square millimetre produces the bastard forms of amber. Electron microscope studies at the Museum of the Earth in Poland discovered that osseous or bone amber was not due to trapped bubbles but a dense formation of tiny cracks which was only intermittently dispersed with bubbles.

As well as turbidity, colour is also a major consideration for all students of amber. The colour range is extraordinarily wide, extending far beyond the typical reddish-yellow we are so familiar with. The colour of amber also changes over time due to the effects of oxygen upon the resin. Pieces of fine translucent yellow amber which have been cut and polished for jewellery will gradually darken, becoming red and eventually completely dark.

Arnold Buffum, in his famous work, ‘The Tears of the Heliades’ has a picture of a fine amber necklace he purchased in Sicily. The book was published in 1896. The colours of the various amber pieces are remarkable. They range through yellow, blue, green and red. The same necklace is photographed in Grimaldi’s book, ‘Amber - Window to the Past’, published in 1996. Each of the pieces now has a uniform brown hue. If the original painting by Buffum is to be believed and there is no reason to doubt it, the colour has completely vanished over a period of 100 years.

Blue amber can be found, predominately in the Dominican Republic. It is also found in the Baltic. An amber researcher Sawkiewicz determined that Baltic blue amber was formed through the optical effect of closely concentrated bubbles of the same size, 0.00007 mm.The author has in his possession a tiny piece which shows some blue colouring and is pictured here. Green fossil resin can be found, again from the Dominican Republic and also in copal from Colombia. Burmite from Burma has a deep red colour.

Natural black amber has not been found. Amber when placed in an autoclave at high temperature and high pressure over a period of 48 hours can be turned black, but the colour is artificially induced. Some pieces of amber can appear naturally black but this is do to soil which was absorbed into the resin at the time of its formation. Jet, which is sometimes called black amber is in fact a fossilised wood originally found and worked in the fishing village of Whitby on the East coast of England it is not a fossil resin.

Reaction to solvents

Several amber researchers have noted the reaction of amber to various organic solvents, the following list is an amalgamation of the work of Rice, Fraquet and Bauer. Amber will dissolve in the following:

Solvents Concentration

Alcohol solution of potash 40-55%
Alcohol 20-25%
Amyl alcohol 20%
Benzene <1%
Benzol 10%
Carbon Disulphide 24%
Chloroform 21-26%
Ether 18-23%
Methyl alcohol 13%
Oil of Turpentine 25%
Petroleum Ether 3%

Bauer notes that amber will dissolve in sulphuric ether and acetic ether. He also states that concentrated sulphuric acid will dissolve amber but only when the resin has been granulated. He goes onto to say that boiling nitric acid will completely dissolve amber. Rice also quotes the two acids working in the same way.

Because of the lack of uniformity in the make up of various ambers using these types of solvents is not particularly reliable as a test for amber and is also destructive. See Types of amber page.