What are the Different Gold Granulation Techniques Historically for Making Custom Jewelry?

Granulation (from the Latin: granum = “grain”) is a goldsmith’s technique in which small spheres of precious metal - called granules - are applied to the surface of a jewel in a pattern. 

How It All Started

The earliest archeological evidence of jewels produced using this method comes from the royal tombs at Ur, in Mesopotamia and dates back to 2500 B.C.

The technique spread to Anatolia from this area, and also in the country of Syria, to Troy (2100 B.C.) and eventually to Etruria (8th century B.C.) Decline of granulation occurred by the gradual disappearance of the Etruscan culture during third to second centuries B.C.

Granulation work was also used by the ancient Greeks, but it was the Etruscan craftsmen who became renowned for this technique (the Etruscans also had a mysterious employment of fine powder granulation with no clear evidence of the use of hard solder).

Granulation is arguably the most enigmatic and alluring of the ancient decorative techniques. Professional Etruscan goldsmiths adopted this technique and perfected it into works of art of unparalleled complexity and beauty, when it was introduced–by master crafts-men Fenici and Greci– to Etruria in the 8th century BC, at a time when knowledge of metallurgy and the use of precious metals was already highly developed.

Excavations near the ancient cities of Rome and Southern Russia (the Kertch and Taman peninsulas, during the first half of the 1800s, dig into ancient Etruscan and Greek jewelry.

These jewels were adorned with granulation. The Castellani Family of jewelers who were very active in ancient jewelry research became aware of the jewelry. The discoveries made from those Etruscan burial sites garnered the most attention because of the fact they utilized extremely fine granules.

Alessandro Castellani examined these artifacts in detail in an effort to figure out how they were made. It was only in the early 20th century, after Castellani’s death, that the conundrum of colloidal/eutectic soldering was ultimately resolved.

Though the secret eluded the Castellanis and their peers, this newly unearthed Etruscan jewelry finally led to an archaeological jewelry revival around the mid-1850s. Techniques of goldsmithing were discovered that allowed Castellani and others to accurately reproduce some of the finest ancient jewelry ever excavated. Despite being completely different from Etruscan methods, many of these techniques produced a more or less acceptable result. Many of these Archaeological Revival jewelry pieces have found their way into important jewelry collections worldwide, along with their ancient counterparts.

Gold Granule Techniques

There are three basic techniques for attaching small granules to a metal surface. Those techniques are hard soldering, fusing and colloidal soldering. The granulation materials are typically high-karat gold and/or silver alloys; alloys considered to be below 18 kt.

Gold and sterling silver are too soft for granulation. The gold alloy to replicate the ancient goldsmith processes is 22 kt as in the original pieces. In each case, the granules themselves must be formed first.

Those bind-ings between the granules and filigree are called ‘colloidal soldering’ and the salines used are carbonates, sulphates or oxides of copper. Empirically, the technique is also described as ‘Chrysocolla’ in Naturalis Historia by Gaius Plinius Secundus, better known as Pliny the Elder, which translates to gold glue. In Italy this dish is called ‘Santerna’.

The decorative approach can be broken down into two broad categories: silhouette and backdrop. In the first case the profiles of the figures, like animals, created by granulated outlines and in the second case the spaces previously created as closed work filigree is filled with granulation.

Granules

The gold granules are created from the same alloy as the metal they will be applied to. One method starts by rolling out a sheet of metal very thin, then using scissors to cut very narrow fringes along its edge.

This is trimmed off so that you have a large number of little squares or platelets of metal. Another approach to make grains was using very thin wire coiled around a thin mandrel, for example a needle. The coil is then sliced into tiny jump rings. This makes very symmetrical rings leading to the production of granules of more equal sizes. The aim here is to create lots of uniform spheres that are 1 mm or less in diameter.

Charcoal power coats the metal platelets or jump rings so they don't stick together when they're fired. The bottom of a crucible is lined with a layer of charcoal and the metal shavings are sprinkled on, trying to keep as uniform a distance between the bits as possible.

After that, you pour in a layer of charcoal powder and metal pieces, until the crucible is three-quarters full. The crucible is heated in a kiln or oven, and the pieces of precious metal deform into tiny balls at the melting point for their alloy. These new spheres are allowed to cool. They are then cleaned in water - or, if soldering technique is employed, pickled in acid.

You definitely would not attain a beautiful design with granules of various sizes. Because it’s not physically possible for a goldsmith to create perfectly matched spheres with identical diameters, the granules need to be sorted before their use. The granules are sorted using several sieves.

Hard Soldering

The process of soldering metal items together depends on the capillary action of a lower melting point solders flowing between the metal to be bonded. Soldering is a process that bench jewelers use to join metals together, it's been used since antiquity. Yet soldering tiny metal grains, however, was problematic.

Solder granules are so small, that they need to be cut into very small paillons and positioned very close to the contact-point between the granule and the metal. Repeating this for hundreds of granules in order to achieve a design would be extremely cumbersome. Soldiers also need a binding agent called flux. Flux is quite bubbly when heated which would easily dislodge tiny items and send granules flying everywhere.

One method to mitigate this issue is to file the solder into a coarse powder and mix it with the flux within a small can known as a rochoir. Goldsmiths must make their own rochoir to use this technique as there is no such tool available on the market.

The surface to which the granules are going to be applied is coated with tragacanth – serving as an adhesive agent – and those granules are placed with the help of a very thin paintbrush. Once dry, the granules are dusted with the flux-solder powder and heated until the solder is able to flow beneath the granules by way of capillary action. Due to this process, a solder residue will remain in the gaps in between the granules which cannot be removed.

The Greeks and Etruscans never employed this method. However, Castellani did make things this way.

Fusing

Welding two metals of the same alloy together without the need for any filler material is fusing. For a good heat spread you need a sheet of metal with about the same thickness as the granules diameter. Once placed with a diluted flux and a fine paintbrush the whole lot is fired in a reducing atmosphere oven.

The granules and the sheet metal fuse at a melting temperature. The grate benefit to this process is that no flux or solder is left over. Because this is an intermediate goldsmithing technique that takes many area of expertise and practice.

That was the method used by the Etruscans in the first millennium B.C. Fusing wasn’t known to the Castellani and his Italian contemporaries.

An even more up to date method of fusing is done with an electric current. This process is known as fusion welding. The electric current goes through each granule, traversing the granule to the base, producing sufficient heat to bond the granules to the object.

One of the advantages of this method is that it can be used on completed jewelry, even on pieces already set with stones. The downside is that in some cases, either the granules didn't pack as closely as was intended and/or the lamp current will find its way to the adjacent granules, leading to more loosely bound interfaces.

Colloidal Soldering

This ancient method used in Etruria is colloidal or eutectic soldering. This method utilizes a colloidal mixture between tragacanth gum and copper salts. This compound reduces the melting temperature of interface of the two metals (the granules and the base) and copper then diffuses in both at the surface of contact. This creates an excellent metallic bond.

Colloidal solder is painted onto the metal surface. They are hand positioned over the outer solder with a fine paintbrush and dried gradually. The jewelry item is processed using the fired method in a lowered atmosphere. From there burn out of the tragacanth finishes, leaving the copper compound salt free.

It is at the temperature of eutectic soldering (890 degrees Celsius) that takes diffused copper into the granules and the base joining them. This needs good timing and a lot of skill.

Because of the copper salts used, this method is sometimes changing chemical soldering.