Goldstone | Meaning and Properties

 

 

goldstone oval shaped cabochon 

What is Goldstone?


Goldstone is a man-made material that's occasionally referred to as aventurine glass although the name is not used as often because it implies an association with the mineral aventurine when in fact from a geological perspective, the two have very little in common.  Thought of by many as being an imitation of aventurine feldspar also known as sunstone, goldstone is characterised by coarse flecks of copper randomly dispersed within glass.  Although the 'gemstone' is mostly found in shades of orange or brown, it can also be navy blue and occasionally green.  Its colour is caused by the presence of copper but in blue goldstone the copper is replaced by an alternative mineral or chemical element which alters the colour of the glass and gives the flecks a slightly different appearance.  With that said, the glass itself is sometimes also slightly coloured.  Green goldstone which although quite rare is produced by using chromium oxide which is also used as a green pigment.  The shape and size of the glittery specs in goldstone tends to be relatively uniform and the distribution is rarely as natural as it is in sunstone and aventurine.

 

 

The Truth about Goldstone


The most famous story about how goldstone came about is a dubious tale which gathered momentum through plagiarism and as a result is now widely believed to be factual.  The true story however is both interesting and quite different.  In the myth it's said that goldstone was produced purely by chance when glass producing monks in Venice accidentally dropped a jar filled with flecks of copper into a vat of molten glass and having solidified, the glass had a spangly or glittery appearance hence the newly discovered material was named avventurina from the Italian word "disavventura" meaning "mishap" or "misadventure".  Depending on the article that you read, the incident is said to have taken place at some point during either the 13th, 17th 18th or 19th century.  Whilst it's well known that an early glass maker from Murano (a group of islands in Venice famous for glass making) attempted to imitate the minerals agate and chalcedony there is no evidence to suggest that he went on to produce goldstone.

Articles that have been written using facts suggest that goldstone was created by Vincenzo Miotti a physicist and astronomer born in 1712 in Murano but the exact formula that he used was not disclosed until his wealthy glass-making family stopped producing glass.  The purpose for finally revealing his formula was likely to have been to kick-start the tradition of manufacturing goldstone once again in Venice.

In the 1860's a new formula was created based on a recipe compiled by French chemist Théophile-Jules Pelouze.  In 1894 Henry Stephens Washington visited a glass making factory in Murano and subsequently wrote 

The manufacture of this glass being a trade secret I could extract any information from the foreman who gave me the specimens as to the process or details of the manufacture; a fact which is greatly to be regretted.
 
Having been given some goldstone he went on to write an account which included specific details about the copper crystals that were used in its production.

Goldstone aka aventurine glass was once again discussed in 1876 by French writer Louis Dieulafait.  With regards to the material which is referred to as aventurine he writes

For several centuries Venice has had the monopoly of the fabrication of aventurine; and even now, it is a Venetian artist, Bibaglia, who furnishes to commerce the artificial aventurine that is most highly prized. Aventurine is a glass the base of which is soda ash, lime, and magnesia, coloured yellow by oxide of iron, and holding in suspension a large number of small particles of oxide of copper. The distribution of these particles in a regular manner through the whole vitreous mass appears to be the chief difficulty in its manufacture. The dexterity requisite to accomplish this must be very difficult to attain, for the profits realized from the manufacture of aventurine are remarkably large.

According to its quality, the artificial gem sells for $5 to $15 the pound, while the raw materials that enter into the composition of a pound of it are certainly not worth a quarter-dollar. French chemists--M. Hautefeuille in 1860, and M. Pelouze in 1865--have published processes by which productions have been obtained equal to that of Venice, and, in the latter case, perhaps superior. The new aventurine of M. Pelouze has a beautiful lustre, and a hardness exceeding that of glass and ordinary aventurine. It is obtained by melting together 250 parts sand, 100 parts carbonate of soda, 50 parts carbonate of lime, and 40 parts bichromate of potassium. It will be seen that by this formula the spangles with a basis of copper are replaced by spangles with a basis of chrome. 

The mineral aventurine is believed to have been named after goldstone because it also exhibits a sparkly appearance caused by the presence of plate-like inclusions of other minerals.  This optical effect has become known as aventurescence. and as well as being used when referring to natural minerals like sunstone and aventurine, it's also used to describe the effect seen in goldstone.