Granulation

921NEC_detail2Pattern, texture, incredible detail — Granulation is the ancient art of fusing tiny spheres of metal onto a backsheet to create interesting patterns. Although the technique itself dates back over 4000 years, the Etruscans of 7th to 6th centuries BC perfected this painstaking art.

Granulation is most often done using high-karat gold (22k or 18k) or pure fine silver. This is necessary because lower-karat gold, sterling silver, and other alloys do not fuse well. In general, granulation works most easily when using granules and back sheet of the same metal.

To get technical for a moment, the granules are fused to the back sheet, not by traditional soldering, but by eutectic or colloidal soldering. A copper compound is mixed into an organic glue solution. The granules are adhered using this glue mixture and allowed to dry. When heated, the copper combines with the metal, creating a skin on the surface of the metal that melts at a lower temperature than the rest of the gold or silver. Thus the granules are fused to the back sheet without melting completely.

Modern technology has changed the practice of granulation somewhat. The ancients probably used tongs, a mouth blowpipe, and charcoal to accomplish their tasks. Modern goldsmiths commonly use a gas torch and electric kiln. Granules are often still made by alternating  layers of tiny gold or silver snips with crushed charcoal in a crucible and heating it in a kiln. Metal will ball up when heated past its melting point. The granules are then washed in a sieve to remove the charcoal dust.