Goldstone Man-Made Stone Properties, Facts and Photos
1. What is Goldstone?
2. Dispelling the Myths
3. Goldstone and Aventurine
4. Article Pictures
5. Shop Goldstone
What is Goldstone?
Goldstone is a man-made material sometimes called aventurine glass. It was known as aventurine glass prior to being called 'goldstone'.
The name is not used that often nowadays because it implies an association with the mineral aventurine.
Goldstone was once used to imitate aventurine feldspar which is sunstone. It doesn't tend to be used for this purpose anymore because it's very easy to tell one from the other.
It's widely reported 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.
The glass is first heated until it becomes molten. Granules of copper oxide are then added to the mixture and dissolve because of the high temperature.
Once fully dissolved the melt is allowed to cool during which time the copper forms octahedral-shaped crystals. The slower the glass cools 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 seen in goldstone is caused as light reflects off the copper crystals.
Although goldstone is best known as an orange-brown coloured stone it can also be navy blue and occasionally green. The glass used in the production of the orange-brown stone is clear. The colour comes from the copper.
In green and blue goldstone the glass is coloured. Instead of specs of copper, cobalt tends to be used to produce blue goldstone and chromium for green.
The sparkling effect in goldstone is best seen with the reflection of light from ambient lighting. Blue goldstone can be more impressive than orange possibly because of its darker colour.
Goldstone Dispelling the Myths
The most famous story about how goldstone was discovered is a dubious tale which gathered momentum through plagiarism. As a result it's now widely 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 word 'disavventura' meaning 'mishap' or 'misadventure.
Depending on the version you read, the incident is said to have taken place at some point during 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's no evidence to suggest he produced the material known today as goldstone.
Factual articles that have been written suggest goldstone was created by Vincenzo Miotti a physicist and astronomer born in Murano in 1712.
The exact formula he used was not disclosed until his wealthy glass-making family stopped producing glass. Their reason for revealing the formula is believed 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 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 which 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.
Goldstone Vs Aventurine
Aventurine is a type of quartz. It's believed to have been named after the material known as goldstone.
Like goldstone, aventurine also exhibits a sparkly appearance caused by the presence of minute inclusions of other minerals.
This optical phenomenon is known as 'aventurescence'.
As well as being used to describe the optical effect in sunstone and aventurine, the word 'aventurescence' is also used to describe the sparkly appearance of goldstone.
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.