Goldstone, Properties, Facts and Photos

What is Goldstone?

Goldstone, sometimes called aventurine glass, is a man-made decorative material.

Before being called goldstone, it was known as aventurine glass, but the name is not used that often now because it implies an association with the mineral aventurine.

Goldstone was once used to imitate the mineral aventurine feldspar which is sunstone.  It's rare to see it used for this purpose anymore because it's easy to tell one from the other.

It's widely reported that goldstone is produced by adding minute specs of copper to molten glass.  Although goldstone is glass filled with copper the way it's produced is far more complex.

Initially the glass is heated until it becomes molten.  Granules of copper oxide are then added to the mixture which dissolve because of the high temperature.

Once fully dissolved, the melt is cooled during which time the copper forms octahedral-shaped crystals.  The slower the cooling process, the larger the crystals.

The shape of an octahedron is like two pyramids stuck base to base.  It's a symmetrical eight-sided shape so the top and bottom are the same.  

Copper oxide, which occurs naturally as crystals, is a chemical compound of copper and oxygen. The mineral cuprite is a copper oxide.

In this photo the octahedron-shaped crystals are cuprite.  
The twinkling effect that can be seen in goldstone is caused by light reflected off the copper crystals.

Although goldstone is best known for being orange-brown, it can also be navy blue and occasionally green.  The glass used for the orange-brown stone is colourless.  The colour comes from the copper inclusions.

For blue and green goldstone, coloured glass is used.  The copper specs are replaced with cobalt for blue goldstone and chromium for green.

The sparkling effect of goldstone is best seen with ambient lighting.  Blue goldstone can be more sparkly than orange possibly because of its darker colour.   

Goldstone Dispelling the Myths

The most publicised story about how goldstone was discovered is a dubious tale that gathered momentum through plagiarism.  As a result, it's now believed to be factual.

The story claims goldstone came about 'by chance' when glass-producing monks in Venice accidentally dropped a jar filled with specs of copper into a vat of molten glass.

Once solidified, the glass had a spangly or glittery appearance.

The accident led to the new material being named 'avventurina' from the Italian 'disavventura' meaning 'mishap' or 'misadventure.

Depending on which version you read, the incident is said to have occurred in the 13th, 17th, 18th or 19th century.
Whilst it's well known that an early glass maker from Murano attempted to imitate the minerals agate and chalcedony, there's no evidence to suggest he produced the material known today as goldstone.

Factual articles suggest goldstone was created by Vincenzo Miotti, a physicist and astronomer born in Murano in 1712.

The formula he used was not disclosed until his wealthy glass-making family stopped producing glass.  Their reason for revealing it is believed to have been to kick-start the tradition of manufacturing goldstone again in Venice.

In the 1860s, 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 following; 

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 that included specific details about the copper crystals used in its production.

Goldstone was once again discussed in 1876 by French writer Louis Dieulafait.  With regards to the material 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 Difference Between Goldstone and Aventurine

Aventurine is a variety of the mineral quartz.  It's believed to have been named after goldstone.

Like goldstone, aventurine exhibits a sparkly appearance caused by minute inclusions of other minerals.

This optical phenomenon is known as 'aventurescence'.

The word 'aventurescence' is also used to describe the sparkly appearance of sunstone and goldstone. 

Article Pictures

The cuprite crystals in our second picture are courtesy of Stan Celestian.  The blue goldstone tumbled stones are from our collection. Both images are clickable.