Granulation (jewellery)

Granulation is an ancient goldsmith's art, are taken as an ornament or an area in the smallest gold beads and then soldered on a gold ground so that they are only connected at their respective points of contact. Light and shadow so create a strong three-dimensional effect. World famous are the Etruscan granulations.

History of the rediscovery

Living in the middle of the nineteenth century Roman goldsmith Augusto Castellani devoted much of its work, the rediscovery of the lost previous ancient technique of granulation, in the European goldsmith's art was applied to the early Middle Ages. He used in his work a powdered solder with which he fastened the sand-like beads on the surface. Due to the capillary force, the liquid solder moved into the spaces between the abutting balls and fused them together as a hermetic surface.

1918 Marc Rosenberg published his book on the technical basis of the history of the goldsmiths and encouraged so that, inter alia, to a new, broad search of the technique of granulation. Chemical studies on antique pieces showed that the base metal and the bullets each had the same fineness. Rosenberg concluded that the connection is made by a kind of "chemical Lot ". He assumed that the melting and afterglow of the balls in charcoal dust this was belittled covered and thus the melting point of around 160 ° C with Goldkarbid, which would allow welding to the base metal.

One of the first who made ​​granulations that could withstand the comparison with their antique models on a technical level, was around 1920 Johann Michael Wilm in Munich. Elisabeth Tresckow began around 1930 in Essen- Margarethenhoehe with the production of granulations on a high artistic level.

Technology

To prepare the balls fine gold scraps and charcoal dust in layers stacked in a fireclay crucible and rinsed after melting in water. It emerged as perfectly round balls of gold. However, the prerequisite for the success here is a gold with a fineness of 900 / ° ° °.

Lower alloys such as 14 carat = 585 / ° ° ° are granulated with copper salts. Copper sulfate, copper oxide, copper chloride or copper are equally suitable for the granulation. They are mixed with a weak solution of organic glue ( hide glue, isinglass, etc.). When melting the copper salt is converted into metallic copper, which is alloyed with the gold, thus forming a chemical solder, which then allows the adhesion of the spheres. Burns the glue while carbon, which enables the reduction of the copper salt to metallic copper.

Such alloys can also be granulated with the aid of dilute Fluoron, a commercially available flow Mitel for brazing of heavy metals, or tragacanth. Here, a much smoother surface than in the granulation with copper sulfate is formed.

Collections

A variety of antique pieces with granulations is exhibited in the State Collection of Antiquities, Department IV, in Munich.

The private collection of Elizabeth Tresckow, which includes both antique jewelry as well as works by his own hand, contains a number of extraordinary granulations. She bequeathed it to the Cologne Museum of Applied Arts, where most can be seen in the permanent exhibition.

• Goldsmithing
• Jewellery Making