GRANULATION
Granulation is a process whereby very small grains (granules) of metal are joined by metallic bonding (fusion) onto metal surfaces in a decorative pattern. The fusing process does not leave any visible trace, even the tiniest granules adhere invisibly and without melting the metal or the granules. The most spectacular and the most subtle effects are achieved by using high karat gold.
The ancient technique of joining metals with non-metallic solders (colloids) relies on the reaction of copper compounds to form a EUTECTIC bond.
A eutectic alloy is composed of two or more metals which has a lower melting point than that of any of the metals which compose the alloy or the alloy itself.
Small metal particles are melted into spherical grains and applied to metal areas to be joined in a mixture with organic adhesives which act as reducing agents to form copper oxide. The glue carbonizes. The oxygen from the copper oxide combines with the carbon to form carbon dioxide gas and reduces the copper oxide to a pure metallic copper film. This film forms a eutectic bond with the granules and the piece, joining them together only at the points of contact. After prolonged heating, the copper diffuses into the gold alloy (there is a molecular exchange) leaving no residue on the surface.
To form granules, wind a very fine wire around a pin. Cut the coil into tiny jump rings and melt on a charcoal block until the rings form tiny spheres. Pickle the granules clean and copper plate them.
Prepare the surface to be granulated. Carefully sand and polish the metal to a mirror finish. Wash and rinse the piece in clear water. Enrich the surface by heating the gold until it oxidizes and then pickle clean and rinse. Repeat the heating and pickling process until the gold no longer oxidizes. There is now a layer of fine gold on the surface. Wash, rinse again and begin to apply the granules.
The granules are placed on the surface with a solution of Hide Glue, liquid hard solder flux and water. Using a 000 sable brush, move the granules into an ornamental pattern. Be careful to use the glue solution very sparingly. An over-accumulation of glue will cause bubbling when heated
and result in granules moving as the glue is burned away.
Place the piece on a ceramic tile on the lid of a hot trinket kiln for a few minutes. When the glue begins to burn and turns brown, carefully place the piece to be granulated on the hottest part of the kiln and allow the glue to burn away completely. Now begin to heat the piece in the kiln using a very soft flame from an acetylene torch. Start by circling the outer edge of the piece, building an even column of heat. Then move the flame directly over the piece and continue to heat with just the very tip of the flame. When the piece glows cherry red, watch the granules closely. Continue heating until you see the copper skin melt off the granules and each granule appears shiny and distinct. The spheres should now be attached. Remove the flame immediately. There is only a second between perfect granulation and melt-down, so move fast!
Remove the piece from the kiln and allow it to cool. It is important to test the granules by carefully pulling each one with a fine tweezers. Be very careful to avoid marking the granules! If some of the granules are not adhered it is necessary to reglue them and refire the piece. When you are certain that they are firmly attached, pickle, clean and rinse. The piece is now ready for further fabrication and finishing.
Photographs by Ralph Gabriner
