Japanese Non-Ferrous Alloys and their Patination
Bethany Weeks
Metals are generally considered by the public to have a narrow range of colors but
metalsmiths have a long history of trying to counter that view. Different alloys allow for a range
of shades between the classic yellow of gold to dark grey of iron. Patination also increases this
range of color. The Western approach to metal coloring is a straight on approach, with direct
application of metal colorants. In contrast, the Japanese are well-known and respected for their
mastery of alloying and patination to color metal without heavy use of external colorants.
Two of the most well known Japanese alloys are shibuichi and shakudo, both of which
are a copper alloy. Shibuichi (四分一) literally translates as one in four which refers to the
amount of silver to copper in the alloy. In actuality, the percentage of silver to copper has a wide
range, depending upon the exact shade or coloring desired. In general, shibuichi contains 15–
40% silver but can range as wide as 2-60%. Depending on the amount of silver, or other trace
elements, shibuichi can have hues of light to dark grey, brown, blue, and/or green. Higher
amounts of silver, creates shiro-shibuichi (白四分一)、literally, white shibuichi and is very pale
in grey color. The silver in the alloy creates a eutectic microscructure surrounding the copper
dendrites. This not only affects the coloring of the metal but the surface finish, which can be
matte with light scattering properties. Different types of this alloy’s crystal growth due to the
different quantities of silver can be see below in figure 1.
Figure 1. Shibuichi surfaces. The figure on the left shows the crystals on an unfinished piece.
The figure on the right is of a piece that has been reduced in thickness by hammering, resulting
in distortion in the crystals. You can clearly see the copper (dark) and silver (light) crystals in
both.
Shakudo (赤銅) is similar to shibuichi except that instead of silver, copper is alloyed with
gold. Generally 3-6% gold is used but as much as 10% can be added and have the metal still
considered to be shakudo. The coloring of shakudo is generally very dark due to the gold added.
The small amount of gold forms into such small particles that they absorb light, creating very
dark brown-black metals that look like lacquered wood. Shakudo can have hues of dark red,
purple, or brown depending on the amount of gold and trace elements added. Due to this
darkening effect by gold, if small amounts are added to shibuichi, it becomes kuro-shibuichi (黒
四分一), which is literally translated as black shibuichi. Some metalsmiths prefer instead to mix
shakudo and shibuichi to create kuro-shibuichi and will generally use a range of 60-85% shakudo
to 15-40% shibuichi.
Due to their ability to create a wide range of colors, shakudo and shibuichi are commonly
used in a Japanese metal technique called mokume-gane (木目金). Mokume-gane literally
translates to metal wood eye or, slightly less literally, metal wood grains. It is a technique that
laminates different metals together into many layers. The layers are then re-exposed by carving
and engraving. A good example of a section view of mokume-game can be seen below in Figure
2.
Figure 2. Mokume-game used in a tsuba with alternating layers of copper (lighter) and shakudo
(darker).
Mokume-gane and other uses for shakudo and shibuichi were most commonly used in the
making of tsuba (sword guards) after the Meiji era. The Meiji era was a great transition for
metallurgy in Japan as it was a time of peace, which forced the tsuba-makers to expand their
repertoire. As a result, instead of focusing on basic iron tsuba, they started creating more
elaborate ones that included the use of mokume-game with shakudo and shibuichi. They also
started making other decorative pieces with the alloys.
Figure 3. Tsuba with mokume-game formed to look like cherry blossoms on water
Figure 4. Tsuba using shakudo background and gold highlight
Figure 5. Shibuichi decorative bowl
Figure 6. Shibuichi decorative piece
Patination is the other key to creating these metal pieces that have this range of coloring,
especially with shibuichi and shakudo. Many of their exotic colorings cannot be obtained
without patination. Patination itself is actually a controlled, or uncontrolled, form of oxidation
and corrosion of the surface of the metal. It can be highly desired in a piece as a sign of natural
aging. However, skilled application of specific recipes can provide a controlled acceleration of
this “aging” by oxidizing the surface. There is a wide range of recipes out there to do this. The
Japanese use a special patination agent called rokusho. It is widely available inside of Japan but
is more rare outside. There are several recipes available for outsiders who wish to make their
own rokusho. One such recipes calls for a combination of copper acetate, sodium hydroxide,
and calcium carbonate mixed with water. The solution is allowed to separate for a week and is
then drained. The remaining formula is rokusho and can be mixed with plum vinegar, or more
water, to make the patination solution. Before patination, the metal must be carefully cleaned
and prepared. Many Japanese metalsmiths will grate daikon (a type of white Japanese radish)
into a paste with 5 parts water and agitate the piece in it as part of their surface preparation. It is
unknown exactly what purpose the daikon serves but the metalsmiths believe it helps to prevent
tarnish, encourage even coloration, and/or activate the patination solution. When the piece is
prepared, the rokusho is mixed with vinegar or water and copper sulfate. The rokusho is brought
to a boil and the piece dipped into it. After dipping, the piece is rubbed with diakon paste again
and then dipped again. This process is repeated until the desired coloring obtained. Rokusho,
particularly makes gold more yellow, silver whiter, copper orange or an orange-red, shakudo
blackened, and shibuichi colored grey depending upon the exact alloy and amount of dipping.
The Japanese Meiji era was an amazing time for metalsmithing, producing a rainbow of
potential colors for metals. Shakudo and shibuichi, in particular, are still being created in Japan
as well as abroad by artists and metalsmiths alike due to their beauty and coloration.
References
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London: Crafts Council. 1982.
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Savage, Elaine and Cyril Stanley Smith. “The Techniques of the Japanese Tsuba-Maker.” Ars
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Shimizu, Yoshiaki. Japan: The Shaping of Daimyo Culture 1185-1868. National Gallery of Art,
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