Precious Metal Alloys Part 2

A variety of colors stands for zest and happiness. In the case of jewelry, these strong emotions have been expressed for centuries using enamel and gemstones. But even precious metal offer an endless variety of color options. Today, individuality is expressed by jewelry in Europe and the USA in particular and jewelry made from different color alloys is seen as contemporary, is easy to combine and reaches a broad target group, irrespective of age.

Steve Midgett: 'Orbit Brooch', titanium and tantalum mokume gane with 22 karat gold inlay and diamond

Giovanni Corvaja: brooch with 26 different 18 karat gold alloys - yellow gold (gold-silver-copper), red gold (gold-copper), white gold (gold-nickel-zink)

On the one hand, gold-silver-copper alloys offer colors ranging from yellow-green to orange-red. On the other, by adding nickel, zinc, tin, aluminum, iron, silicon and arsenic and producing inter-metallic compounds, crazy and fascinating colors can be created such as bright blue and black gold. Another colorful adventure is created with copper alloys containing precious metals and their permanent chemical surface reactions after chemical or heat treatment. These create decoctions, oxide layers or annealing colors or the black color which forms when silver or silver alloys tarnish. To obtain more colors, the broad range of goldsmithing techniques are applied which involve the application of heat. Soldering, sintering and diffusion bonding are all used. The varied group of mechanical links such as riveting, folding and pressing, etc. must be excluded here along with electrolytic coating and metallization with metal oxide. Colors of a toys are an important issue in the enjoyment and complex science that underlies metallurgical research in the jewelry sector. Metal separation institutes worldwide have developed various alloys, although it's mainly the alloys with good processing characteristics which have succeeded.

Gold alloys, which were launched onto the market as inter-metallic alloys in unusual colors such as luminous blue and violet, cannot unfortunately be reshaped and can only be sawn down or filed. Inter-metallic compounds are homogeneous compounds of metal. They display characteristics which are very different from those of the individual alloy components. Inter-metallic compounds are usually very hard and brittle and have a high melting point.

In some countries, strict acts on assaying set the boundaries for metallurgy. Laws vary greatly from country to country and must be checked in detail. The strict laws on assaying in England, for example, were reformulated in April 2007 to take account of the fact that more and more jewelry and watches are being created from different alloys.

Claus Bury: 'Rectangle 1', brooch, 1977. Gold, silver, copper alloys

Matthias Lehr: caviar bowl (two bowls in one another) with spoon and cooling gap for ice. Corinthium Aes - black bronze with gold content, silver

Matthias Lehr: self-built oven for melting

Combined through fire and the oven

Gold creates wonderful color combinations when combined with silver, platinum, palladium, white gold and copper or steel, amongst others. When metals are diffusion bonded, the join is more secure than with soldering. Diffusion bonding is the process of welding e.g. sheet metal under pressure far below the temperature of soldering. The important parameters for diffusion welding and sintering are the sintering temperature, surface pressure and welding time. Sintering is the heating of metal powder until the particles adhere to each other. With diffusion bonding or sintering stress relieved and largely homogeneous bonds are created, as is the case with mokume gane. One possibility for diffusion welding is the table sintering equipment by the company Frisch. Some goldsmiths, however, carry out sintering in ovens they have built themselves. A hotly debated topic in diffusing is that completely diffused layers can become detached from one another again under the strong pressure applied by rollers when producing mokume gane sheet metal. Stewart Grice, mill and refining d rector at Hoover & Strong, USA wrote in the publication of the Santa Fe Symposium of 2006 how this delamination is caused: "Combining 18 karat yellow gold with platinum alloys he suggests not to quench after heat treatment but to do cold pressing after firing and to anneal at least for one hour and to use a platinum alloy with a recrystallization temperature as low as possible."

The relation of a long-lost alloy and Japanese copper alloys

Researching recipes for alloys and chemicals, the development of tools, etc. is all part of the craft of the goldsmith. Claus Bury and Mathias Lehr are two individuals who have been persistent in answering open questions. Today, Claus Bury is a sculptor with a teaching position at the Nuremberg Academy but he began his career by training to be a goldsmith. Painting led him to seek the same variety of colors in precious metals during his scholarship at the 'Scheideanstalt Degussa' for metal separation.

In 1996 in collaboration with Dr. A. Giumlia-Mair, an archaeologist and archaeometallurgist, the goldsmith Matthias Lehr began to reconstruct one of the long-lost alloys - Corinthium Aes - a bronze alloy containing gold and arsenic. Dr. A. Giumlia-Mair: "Referring to antique resources there were personalities murdering for corinthium aes pieces in Roman time like the emporer Augustus.

The oldest identified objects come from Egypt like the crocodile " El-Faiyum " in the Egyptian collection in Munich. Dr. Giumlia-Mair: "Corinthium Aes came to Korea and Japan in a roundabout way, where it was perfected. In Japan, traditional copper alloys containing precious metal remain through to today". These are becoming ever more famous through the mokume gane technique. The alloys obtain their typical colors through patinating with fluids from coarsely grated radish, copper salts and vinegar. The copper alloys with their precious metal content are often inlaid with silver or fine gold to create beautiful contrasts. Matthias Lehr: "It's very hard on the goldsmith to see the gold disappear into the melted bronze".

Deborah Krupenia: necklace 'Rhythmical Pectoral', after Paul Klee, four shibuichis, shakudo, 22 karat gold, Japanese silk cord married metals, fabricated, etched, patinated

Deborah Krupenia: two brooches. 'Ceremonial Time' (top) tilling, field of copper with oval  dots of 18 karat green and 22 karat yellow gold, kuromi do, 98/2 shibuichi 'Gray Values I' (bottom) 85/15 and 60/40 shibuichi, 18 karat yellow and palladium white gold

Atelier Zobel: welding of platinum splinters to 18 karat yellow gold

Atelier Zobel: brooch, red gold, platinum, diamonds, sapphire

David Huang: bowl/object 'Whorled Flow', fine gold, silver, copper, patina: silver nitrate solution applied to heated metal, hot wax finish

Patination of copper alloy containing precious alloy

A patina is the oxidation of metal surfaces. Japanese alloys use specific recipe mixes to create mysterious color tones such as red-gray and violet-black. The artist Deborah Krupenia uses a range of different alloys herself with 50 to 60 g maximum for her setup. She says: "Although I don't have the same controlled environment when alloying as the metal separation institutes do, I can make a wider range of alloys (e.g., shakudo 5%, 10%, 15%, 20% gold) with subtle value changes. I have a small stock of kuromi do (copper with 1% arsenic) from Japan." The patinated bowls and tea pots by David Huang are forged from copper and have silver edging and fine gold foil inside. David Huang: "To protect myself from the fumes while applying the patinas I work outside and wear a respirator. I also prefer heating the piece with a torch and applying the solutions with a brush to the hot metal as opposed to using spray bottles. I find it wastes less of the chemicals and produces less mess."

Fusing, soldering and welding

Yellow gold can easily be melted down in platinum due to the great difference in the melting point. Soldering and welding red gold with platinum can cause problems as the expansion is very different when warmed and subsequently cooled. "When gold is welded with platinum, the items of jewelry can become warped. This is due to the different melting temperatures and thermal expansion coefficients. We use this effect as a design element at our workshop" says Peter Schmid, proprietor of the jewelry design workshop Atelier Zobel. The antique Korean technique of Keum-boo is the oldest Korean technique for welding thin fine gold foils to silver or other metals. Christine Dhein, goldsmith and co-director of the Revere Academy in San Francisco has published two DVDs about this (see book review section 'Spots'). The finest wires are worked into brooches by Gill Galloway-Whitehead, creating the effect of miniature paintings. She transforms the flat Keum Boo technique onto wire. Gill Galloway-Whitehead herself says that working with fine wires enables her to paint with metal: "Using the whiteness of fine silver in combination with the rich yellow of fine gold as well as the black through to gray of oxidation gives a satisfying color palette with which to work."

Gill Galloway-Whitehead: brooch, oxidized fine silver wirework, fine gold confetti

Christine Dhein: steel or nickel sheet on electric hot plate, tweezers, agate burnisher - applying keum-boo gold foil to a flat surface

Chistine Dhein: tools for cutting keum-boo gold foil, clock-wise from the upper left: craft punch, vellum, tweezer, paper punch, Joyce Chen Ultimate Scissors cooking shears, craft scissors

Christine Dhein: 'Swirling Waves Pendant', oxidized sterling silver and fine gold foil

Oxide layers and decoctions

Oxide layers, known as annealing colors, rub off with use, apart from with titanium and aluminum. Even the layer of silver and copper sulphide which results from silver tarnishing/sulphidizing is a layer of oxide and rubs away with time. A potash sulfurated solution can be used to tarnish silver or a preparation such as 'Paris oxide' which contain sulphur. According to Christian Cretu and Elma van der Lingen, gold alloys with a minimum of 18 karat copper can also be surphidized in this way. They wrote in one of their papers "Black gold generally contains cobalt. An olive-green hue of 18 karat gold contains cobalt with chromium additions." The jeweler Ludwig Muller from Geneva developed and patented a blue gold alloy. It is gold and iron which is temperature treated so that the iron molecules oxidize at the surface area.

With whitening or yellowing, the oxidized copper portion created during soldering or annealing is dissolved e g. in the sulphuric acid pickle. Pure silver or pure gold-silver alloy remains at the surface of the item. Only a agate or steel burnisher is used for polishing here, and not with a polishing machine, so that the decoction is compacted and not worn away. With soldering, the decoction must be removed from the soldering points beforehand for a good bonding.

www.atelierzobel.com

www.gillgallowaywhitehead.com

www.kochgalerie.de (Mathias Lehr)

www.davidhuang.org

www.christinehein.com

www.mokume.com (Steve Midgett)

www.c-hafner.de

www.schichtwek.com

www.reactivemetals.com

www.frisch-gmbh.de

Patination: Matt surfaces are good for patinas and can be prepared through various processes e.g. cauterization, steel wool, fine sandpaper, wire brushes or blasting with sand or fine glass beads. It is absolutely essential to wear rubber gloves when creating an even patina so as to avoid oils from the skin being added to the object. The alloys are either immersed in or painted with the patina. The difficulty with all patinas is making them stable and durable and to protect the patina from progressive oxidation through the oxygen in the air. The chemicals used to create the patina must be constantly well rinsed to prevent chemical reactions occurring. Particularly good protection is provided by only using the patination in indentations to prevent rubbing. Deborah Krupenia uses Renaissance Microcrystaline Wax Polish to seal her patinated jewelry. She says: "Occasionally, a piece needs to be cleaned. I use a slurry of Bon Ami, which is a gentle household cleaner (calcium carbonate), applied with a Japanese brush. Then I rewax." The Japanese artist Eitoku Sugimori explains recipes in detail especially for the goldsmith in his book "Japanese Patinas" (see book review section Spots).

Japanese precious copper alloys

Here are a few typical copper alloys containing precious metals, widely used in Japan, in their different mixing ratios and with the color they create when patinated with the traditional Japanese recipe of 'Rokusho', according to Hiroko Sato and Gene M. Pijanowski:

Shakudo: fine gold (e.g. 4.8%) and pure copper, dark violet to black

Shibuishi: fine silver (e.g. 40%) and pure copper (60%), gray

Shiro-Shibuichi: Shakudo (60%) with Shibuichi (40%), light gray

Kuro-Shibuichi: Shakudo (83.3%) with Shibuichi (16.7%), dark gray

Kuromi-do: arsenic (1%), pure copper, dark brown to black

Safety tips

• only use acid-resistant containers
• acid on water, never water on acid
• wear acid-proof gloves, clothes (long-arms), apron and face protection/protective glasses
• ventilate area well, use fume hood or gas mask to avoid inhaling poisonous fumes
• obtain information on the chemicals from the vendor and health office