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Gold used as decoration on the surface of jewelry by affixing the gold in minute grains to the metal base, sometimes massed in an area of the piece but sometimes placed in linear or outline decoration or used to make a design in reverse silhouette by covering the background of the design.
The grains were made by pouring into water molten gold which then formed drop-like granules, or by placing gold cuttings in a crucible with charcoal and then heating and rotating so that the gold formed small spheres.
The process of gold granulation was used from the 3rd millenium BC by the goldsmiths of the Eastern Mediterranean region and in Egypt, and was carried on and refined especially by the Etruscans. The gold granules were made separately and apparently soldered on, but by a technique whereby the soldering was invisible.
In the finest Etruscan examples, minute gold granules (sometimes only 0,25 mm to 0,14 mm in width) were sprinkled on the surface but in later examples larger grains were used. The Greeks also used the style.
The style (although not the early technique) was adapted in Rome, c. 1826, by the goldsmiths Fortunata Pio Castellani who, with his two sons, developed a process of soldering gold grains on the surface of jewelry; the art was carried on by Carlo Giuliano. The style was again used as decoration for Victorian jewelry. The Etruscan technique, long forgotten, was rediscovered and patented in 1933 by an Englishman, H. A. P. Littledale, and called Colloid Hard-soldering.
A more recent technique was developed in Rome by F. Magi and V. Federici, involving making the gold granules by pouring molten gold from a height onto a stone slab, after which the granules were welded to the metal object by resin under red heat, the tars in the resin acquiring adhesive properties. It is sometimes referred to as 'granulation'.
From: An Illustrated Dictionary of Jewelry, autor: Harold Newman, publishers: Thames and Hudson