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{{Short description|Traditional Japanese chemical compound}}
{{italics title}}

{{Missing information|Traditional manufacturing methods and modern commercial manufacturing methods|date=September 2010}}

{{Nihongo|'''''Rokushō'''''|緑青}} is a traditional [[Japan]]ese chemical compound used in the ''[[niiro]]'' process for artificially inducing [[patina]]tion in decorative non-ferrous metals, especially several copper alloys, with the results being metals of the ''[[irogane]]'' class. It is most commonly translated as [[malachite]]; in art, ''rokushō''  was the most widely used green pigment.<ref>{{Cite journal |last=Plate |first=Maria Katharina |last2=Eyb-Green |first2=Sigrid |last3=Baatz |first3=Wolfgang |date=2020-12-16 |title=The Colour of Pine Needles and Nightingales. A Traditional Japanese Copper-based Green Pigment |url=https://www.degruyter.com/document/doi/10.1515/res-2020-0011/html |journal=Restaurator. International Journal for the Preservation of Library and Archival Material |language=en |volume=41 |issue=4 |pages=253–275 |doi=10.1515/res-2020-0011 |issn=1865-8431|url-access=subscription }}</ref> 

These "colour metals", virtually unknown outside [[Japan]] until the late 19th century, have achieved some popularity in craft circles in other parts of the world since then.

==Usage==
''Rokushō'' is used to treat a number of metals, including raw natural copper, which holds impurities, purified copper, and copper alloy mixes with two to five metals, to produce ''irogane'' metals, including: ''[[shakudō]]'', an alloy of copper and gold, which becomes black to dark blue-violet; ''[[shibuichi]]'', an alloy of fine silver and copper (in a higher percentage than sterling), which turns grey to misty [[Aquamarine (color)|aquamarine]] or other shades of blue to green; ''[[kuromido]]'' which becomes dark coppery black.

''Rokushō'' was generally used to patinate all types of ''[[mokume-gane]]'' ("wood grain metal") as well.

Although other patination agents can be used on these metals, some artisans prefer the rich colors achieved with traditional ''rokushō'' in the ''niiro'' process.

These metals are becoming increasingly popular in high-end artistic jewelry, especially in bi-metals (a layer of the alloy fused to another metal such as sterling).  Because rokushō has a dramatically different effect on sterling silver than on the alloys typically fused to it in bi-metals, a common technique in art jewelry is to engrave through the alloy layer in a pattern to reveal the silver underneath prior to patination.  This provides a rich contrast in color, highlighting the pattern.

==Formulation==
The formulae for rokushō are not published widely or freely, but passed on in the Japanese craft tradition.  However, some scholars have analysed samples of the material.

Premixed rokushō can be purchased outside Japan through specialty jewelry suppliers. Additionally, several different formulas have been proposed to replicate the traditional product for those who prefer to make their own:

* In a container made of glass, porcelain, or copper, dissolve 6g [[copper acetate]], 2g [[calcium carbonate]], and 2g [[sodium hydroxide]] in 150ml water. After a week, siphon or decant the clear liquid from the top; just before use, add another 2g copper sulfate.{{clarify|reason=1) text says "add another 2g copper sulfate", but this is the first instance of copper sulfate in the recipe, 2) calcium carbonate is not soluble in water|date=June 2015}}
* Dissolve 4g copper acetate, 1g [[copper nitrate]], 1g [[cupric chloride]], and 4g [[copper sulfate]] in 1 liter of distilled water.
* Dissolve 60g copper acetate and 60g copper sulfate in a 2-liter solution of [[white vinegar]] diluted 5-12% with water.

Rokusho is not used alone, but mixed with one or more other chemicals.  Further, metal to be processed is cleaned in advance of treatment, using a mild acid bath ([[Oxalic acid|oxalic]] or [[Sulfuric acid|sulfuric acids]] are frequently used), scrubbing with [[daikon radish]] or [[pumice]], and/or a surface abrasive, and often treated after patination also.

==References==
{{reflist}}

==External links==
* [http://www.jimkelso.com/japanpatina.html/tutorial.htm Japanese traditional patina tutorial by crafter Jim Kelso]

{{DEFAULTSORT:Rokusho}}
[[Category:Irogane]]
[[Category:Artistic techniques]]
[[Category:Decorative arts]]
[[Category:Metallurgy]]