Granulating Systems

What is metal granulation?

Granulation (from Latin: granum = “grain”) is a goldsmith‘s technique whereby the surface of a jewel is decorated with small spheres of precious metal, named granules, according to a design pattern. The oldest archeological findings of jewels made with this technique were found in the royal tombs of Ur, in Mesopotamia and go back to 2500 B.C. From this area, the technique spread to Anatolia, in Syria, to Troy (2100 B.C.) and finally to Etruria (8th century B.C.). It was the gradual disappearance of the Etruscan culture between the third and second centuries B.C. that was responsible for the decline of granulation.1 The ancient Greeks employed granulation work as well, but it was the craftsmen of Etruria who became famous for this technique due to their mysterious deployment of fine powder granulation2 without apparent use of hard solder.

Granulation is probably the most mysterious and fascinating of ancient decorative techniques. Introduced by craftsmen Fenici and Greci to Etruria in 8th century BC, where the knowledge of metallurgy and the use of precious metals were already at an advanced stage, expert Etruscan goldsmiths made this technique their own to create works of art of unequaled complexity and beauty.

During the first half of the 1800’s several excavations were carried out in the vicinity of Rome (Cerveteri, Toscanella and Vulci) and Southern Russia (the Kertch and Taman peninsulas) which revealed ancient Etruscan and Greek jewelry. These jewels were decorated with granulation. The jewelry came to the attention of the Castellani Family of jewelers who were very involved in ancient jewelry research. The finds from the Etruscan burial sites attracted the most attention due to their use of extremely fine granules. Alessandro Castellani studied these artifacts in great detail in order to attempt to unravel their method of fabrication. It was not until the early 20th century, after Castellani’s death, that the puzzle of colloidal/eutectic soldering was finally solved.

Although the secret remained a mystery to the Castellanis and their contemporaries, the newly discovered Etruscan jewelry sparked an archaeological jewelry revival circa 1850’s. Goldsmithing techniques were discovered that enabled Castellani and others to faithfully reproduce some of the finest ancient jewelry ever excavated. Many of these techniques were quite different from those employed by the Etruscans yet still yielded a passable result. A number of these Archaeological Revival jewelry objects are now in important jewelry collections around the globe, along with their ancient counterparts.

GRANULES
The granules are made from the same alloy as the metal to which they will be applied. One method begins by rolling out a very thin sheet of metal and scissoring very narrow fringes along the edge. The fringe is trimmed off and the result is many small squares or platelets of metal. Another technique for creating grains uses very thin wire coiled around a thin mandrel, like a needle. The coil is then cut into very small jump rings. This creates very symmetrical rings that result in more evenly sized granules. The goal is to create many spheres the same size having a diameter of no larger than 1 mm.

The metal platelets or jump rings are coated in charcoal powder to prevent them from sticking together during firing. The bottom of a crucible is covered with a layer of charcoal and the metal bits are sprinkled on so they are as evenly spaced as possible. This is followed by a new layer of charcoal powder and more metal pieces until the crucible is about three-quarters full. The crucible is fired in a kiln or oven, and the precious metal pieces warp into small spheres at the melting temperature for their alloy. These newly created spheres are left to cool. Later they are cleaned in water or, if a soldering technique will be used, pickled in acid.

Granules of uneven sizes would not generate a pleasing design. Since it’s impossible for a goldsmith to create perfectly matched spheres of the exact same diameter, the granules must be sorted prior to use. A series of sieves are used to sort the granules.

How do you make gold shot?

Is the process of making gold shot just pouring off molten gold slowly into water after you've heated it? Or do you do it all at once? Whats the purpose of making gold shot instead of ingots ect.

Gold shot is not created by pouring from the lip of a container. It must be discharged through a nozzle. You can make a simple one by drilling a small hole (1/8") in the bottom of a melting dish, which would then be mounted over your container of water, with a torch playing on the dish, around the hole. That prevents the gold from freezing in the dish when it is transferred from the melting dish in which the gold powder is melted. For reasons that have always been hard for me to understand, that forms shot, instead of cornflakes.

Shot is preferred by those that use gold, for it makes weighing out the desired amount easy. Wise goldsmiths don't melt a lot of gold at one time, otherwise it could lead to defective castings (gas inclusions).

By melting only the amount that is needed, the small amount left over (the sprue) can be melted with the next batch, assuring that re-melted gold doesn't accumulate.

The problem with melting gold time and again is that the base metal (typically copper, but not restricted to copper) oxidizes and begins creating gas that accumulates in tiny pockets in castings. Most every jeweler that does casting has had that experience, and often accounts for why they won't, or don't prefer to use gold that has been used previously.