​The National Research Institute of Cultural Heritage (NRICH, Director General Kim Yeonsoo) under the Cultural Heritage Administration (CHA) of Korea succeeded in reproducing the artificial inorganic pigment ‘Dongrok(copper green rust)’, which was mainly used not only in Dancheong for wooden architectural buildings but also in hanging Buddhist paintings, and murals of temples, etc., through a traditional manufacturing technique.

* Dongrok (Copper green rust, 銅綠): A green pigment made from oxidized copper naturally or artificially

* Artificial inorganic pigments: Powder-type pigments produced from compounds with changed physical properties by artificially synthesizing natural inorganic substances such as metal.

The NRICH has been conducting 'Research on Manufacturing Techniques of Traditional Dancheong Pigment and Quality Standards' since 2014 to cope with problems of discontinuity in traditional Dancheong pigments. The NRICH succeeded in reproducing seven kinds of natural inorganic pigments such as Sukganju(red ocher), Hwangto(yellow ocher), Neorok(celadonite), Seogcheong(azurite), Jusa(cinnabar) through the research, and scientifically investigated manufacturing techniques of traditional pigments which is called Subibeop(水飛法) and Yeonpyobeop(硏漂法), and established the manufacturing process.

* Natural inorganic pigments: Powder-type pigments manufactured by processing rocks, soils and shells naturally formed without any chemical change

* Subibeop (水飛法): Manufacturing technique of pigments using the property that the sedimentation rate is different depending on the particle size of the pigment in water or glued water

* Yeonpyobeop(硏漂法): Manufacturing technique of pigments using a bamboo container and glued water

This research aiming to restore materials and manufacturing techniques for traditional artificial inorganic pigments was conducted from 2019 to 2022, following the research on natural inorganic pigments for Dancheong. Representative traditional artificial inorganic pigments include Dongrok, Heocheong(smalt), Miltaseung(litharge), Yeondan(lead red), and Yeonbaek(lead white). Among them, it has been difficult for Dongrok to be restored thus far because the material and manufacturing techniques were not identified clearly unlike other pigments.

Dongrok has been referred to as 'Hayeob' as a pigment color and mainly recognized as atacamite and copper chloride through the scientific analysis, but it was not identified whether it was a natural pigment or an artificial synthetic pigment. Therefore, the name and manufacturing techniques were explored through old literatures to reproduce the pigment, and the characteristics of the reproduced pigment were analyzed to identify the materials.

* Hayeob (荷葉): A green colored pigment with a dark green color like a lotus leaf

* Atacamite: Secondary mineral in green color that has been changed from copper mineral in a dry state or in a salt-containing acid state

* Copper chloride: Compound of chlorine and copper

As a result of the data investigation into ancient Korean, Chinese, and Japanese literatures, the manufacturing techniques for the Dongrok pigment were identified in documents such as Tiān gōng kāi wù (天工開物), Compendium of Materia Medica (本草綱目), Lín yuán jīngjì zhì (林園經濟志), and Newly Revised Materia Medica (新修本草). In terms of manufacturing techniques of Dongrok, the acid corrosion methods which corrode copperware with vinegar was mainly found in the records, and the salt corrosion method which corrode copper powder with bright salt and sal ammoniac was also identified.

* Bronzeware(銅器): A bowl or object made of copper or copper alloy

* Vinegar (醋): A liquid containing acetic acid (醋酸)

* Bright salt: Halogenated mineral salt

* Sal ammoniac (硇砂): Natural ammonium chloride (NH₄Cl) that exists in volcanic or hot spring areas

Accordingly, in order to reproduce the manufacturing techniques of traditional pigment Dongrok, the acid corrosion and salt corrosion methods were sequentially attempted. ▲ Through the investigation and analysis on ancient literature records and traditional Dancheong pigments in cultural heritage, the research was conducted on reproduced materials and standards, and ▲ experiments to reproduce traditional manufacturing techniques and reproduction conditions were secured, and ▲ the analysis on the characteristics of reproduced pigments was carried out. As a consequence of efforts for four years, traditional manufacturing techniques with ensured reproducibility and quality were secured.

As a result of analysis on the characteristics of the reproduced pigments, it was identified that the Dongrok pigment reproduced by the salt corrosion method using pure copper and copper alloy powders (5 types) as raw materials has the same color and components as the Hayeob which was used for traditional Dancheong in cultural heritage and showed a similar particle shape. In particular, as a result of the weatherproof test, the color after deterioration was shown to be similar to that observed in the traditional Dancheong in cultural heritage so that it can be known that the pigment was restored with high reliability.

The Hayeob color is quite frequently used not only in traditional Dancheong, but also in hanging paintings, murals of temples, and portraits in the Joseon Dynasty together with natural inorganic pigments. The research outcomes have great significance for the definition of materials and identification of the characteristics of Dongrok which is the pigment of Hayeob color widely used in colored various cultural heritage for a long time. In addition, those results are expected to contribute to invigorating related industrial fields by securing discontinued traditional manufacturing techniques of Dongrok.

In future, the NRICH is planning to compile the research on manufacturing techniques of traditional Dancheong pigment and present it to the relevant academic world, and make detailed research outcomes open to the public step by step such as the application for patents of the manufacturing techniques, technology transfer and publication of a comprehensive reports. In addition, The National Research Institute of Cultural Heritage under the Cultural Heritage Administration will make efforts to enhance the authenticity of materials for the repair and restoration of cultural heritage and to improve the quality of repairs by steadily working on the restoration research on traditional materials.