Introduction to Japanese Alloys
Though the history of metalworking is relatively young in Japan, craftsmen there developed alloys and the art of patination further there than any other metalworking culture. Their invention of specialized alloys allowed them to produce unique patinas. Today, metalsmiths are still experimenting with alloys, creating new ones, and improving on traditional combinations. In making these alloys, careful consideration of the desired results are given much attention, for small changes in ratios can have dramatic effects on the results.
Japanese artists have contributed significantly in another way, by using their unique alloys in innovative combinations. Perhaps the best example of this is mokume-gane, a lamination process in which layers of various alloys are manipulated to create a rich pattern. In addition, Japanese work of many periods shows highly skilled inlay techniques where, again, the complex pallette of Japanese alloys is used to achieve subtlety and a controlled use of color.
For most of the history of metalsmithing, workers were forced by necessity to make their own alloys. In earliest times, the now distinct skills of refining, alloying, moldmaking and casting were all rolled together into the profession of the metal artist. Still today, even though there are many fine alloys commercially available, it is not uncommon for artists to make their own alloys. Sometimes this might be done to improve the ability of the metal to flow into a mold, or to increase its strength, but another practical reason to manipulate alloys is to influence the way they react to patina solutions.
Making Alloys (Sara-awase)
Most alloys used in cast sculpture contain copper as the principal ingredient. The practice of making alloys goes back to the earliest work, perhaps starting with an alloy of copper and tin, called in Japanese sei-do . This material is an example of the mysterious nature of alloys. Copper, do , is orange in color, has a high melting point, and is quite soft. The other component, tin, suzu, is white, melts at a low temperature, and is even softer. And yet, when these metals are combined, they create a yellow-colored alloy that has a high melting point and is quite tough. Early work in copper was confined to ornaments and ritual objects, but with the development of bronze, the alloy of copper and tin, it became possible to produce durable weapons, agricultural tools, and utensils. It is not surprising that this remarkable alloy gave its name to an entire epoch: the Bronze Age.
It is commonly thought that copper was the first metal that was worked by humans because it can be found as nuggets, is relatively plentiful, and is easy to work. Excavations in the highlands of Turkey conducted in the 1960s revealed numerous copper beads and other ornaments dating from 6300-5500 BC. This demonstrates that even in these ancient times, the skills of smelting, casting, and forging existed. It is probably accurate to say that all metalsmithing as we know it today can be traced back to copper. Copper has also provided the base for many important alloys.
This large family of alloys, also called sei-do or ko-do in Japanese, is a mixture of copper with a low-melting white metal such as tin, zinc, or lead. In early times, tin-bearing bronze was probably the most common alloy, but in modern times most bronze contains zinc. This also applies to zinc-bearing brasses that are incorrectly called bronze.
Just as copper was the first metal to be worked by our ancestors, bronze was the first alloy that they mastered. It combined the easy workability of copper with increased strength, a wide range of colors, and a resistance to corrosion. Also, bronze is much easier to cast than copper because it doesn’t oxidize as much when melted.
Sahari is an alloy of copper (87%) and tin (9%), with small amounts of zinc, lead, and silver. It is famous for the rich tones that can be produced when an object of this alloy is struck. As far back as the Nara period in Japan (710-784 AD), this metal was widely used to make gongs, ( dora in Japanese) and temple bells. Another popular use of this alloy was to make spoons and bowls. There is evidence that the metal was cast into a given shape then refined with forging and ornamental embellishment. The metal has a gray color that is typically left without patina.
Before attempting to create a patina on cast bronze, the metal is subjected to a surface refining process called yaki-namashi . During this process, the metal is heated to remove lead and then cooled gradually. This compensates for the unequal distribution of alloy constituents in the casting, creating a uniform surface that will respond predictably to patination.
Brass, also called shinchu in Japanese, is an alloy of copper and zinc. Objects made of this alloy date back to the Nara period in Japan , 710-784 AD. By definition, brass contains copper and zinc-by altering the proportions, many variations of brass are possible.
(70% copper and 30% zinc) This is by far the most commonly used brass in our time. It combines malleability, strength, and color. It is also called cartridge brass (used for ammunition casings), yellow brass, and by its industrial designation, Copper Alloy 260. As the copper content goes down, the color of the resulting brass becomes pale and patinas are harder to achieve. High zinc brasses (over 30% zinc) are quite tough, and are used for machine parts, valves, and fittings on ships (because of their resistance to corrosion). These alloys are not widely used in the arts.
This is perhaps the best known of the specialty Japanese alloys. It is made by melting together 3-5% pure gold with the balance being copper. The metal can be worked with traditional metalsmithing techniques, and is used for jewelry, small castings, and ornaments such as sword furniture. To develop a dark purple patina, warm the finished piece and immerse it in a hot niage solution.
When the proportion of gold is raised to between 5 and 7%, the alloy is called murasaki-gane. Working properties are similar, but the color achieved with a niage solution is darker than with shaku-do.
This is another alloy unique to Japanese metalworking, and one that is highly respected around the world. The name comes from ichi, which means “one,” and shibu, which means “four.” The alloy consists of one-fourth silver and three-fourths copper, sometimes with a percent or two of pure gold added. Because the alloy is prone to reticulation, it is also known by the Japanese name oboro-gin, (“hazy moon”) which refers to the irregular surface texture . These proportions are open to manipulation. For objects with a lot of surface work such as repoussé, add more silver to the alloy. For castings, the percentage of silver might go as low as 7-15%.
Kuromi-do alloy contains 99% copper, 1% arsenic . This alloy is used as an alternate material to the more expensive gold-bearing alloy called shaku-do . The color of kuromi-do is not the same as shaku-do , but they both produce a lustrous deep black.
It seems likely that the origins of this alloy came from a traditional method of refining copper and lead. This process had as a by-product the material known in Japanese as azuki-shiromi , a material that contains iron, copper, antimony, and arsenic. It is the arsenic that is most important in kuromi-do. This alloy is mainly used for forging, because of its excellent malleability (as one would expect from the copper). When a small amount of gold (2%-3%) is added to kuromi-do , the alloy (called budo-awase) can attain the rich purple-black hue associated with shaku-do . This alloy is dangerous to make in the studio because arsenic is poisonous. Unfortunately it is difficult to buy commercially, and recent attempts to locate a distributor found it available only by special order.
“White Brass” (Haku-do)
Haku-do is a term that applies to a family of alloys rather than a single formulation. The term itself explains the family: Haku means “white” and do means, “copper.” As this implies, the metals in this group have copper as the major component, mixed with some combination of zinc, tin, and/or nickel. The bronze used for casting in ancient times contained 70%-85% copper and 15%-30% tin and was called kyo-do (copper mirror). It falls into the haku-do family.
Yo-haku is the alloy known in the West as German Silver. It contains 10-30% nickel, and 15-30% zinc with the balance being copper. It is accurate to describe this as “white brass,” since it is made by taking a modern brass (copper + zinc) and adding nickel to change the color from yellow to white. When used for casting, 5-10% lead is added to improve the ability of the alloy to flow into a mold. Manganese is added to the melt to reduce brittleness. The color of this alloy will be silvery to gray, depending on the proportions of zinc and nickel. Neither of these alloys offer much opportunity for patination, but the white color is sometimes used to create a contrast to patinas on other metals in the same piece.