BLACK COPPER of YUNNAN H. BRUCE COLLIER1 West China Union University, Chengtn, China
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T WAS a small ink-box in an antique shop that first attracted my attention. Its surface was a lustrous black, with a delicate pattern inlaid in silver, presenting a most striking appearance. Attracted by the beauty of this ware, which I learnsd was called Wu T'ung (black copper) and was manufactured in Yunnan Province (southwest China), I collected a nnmber of pieces, not realizing until some time later that they presented a problem for the chemist. Most of the articles made of this black copper are boxes for ink or tobacco (Figure I), although pen holders, jewel cases, and even cigaret cases are occasionally seen. The designs are largely symbolic, but landscapes and inscriptions are also common. Around the sides of many of the ink-boxes are found depicted the "Four Friends," the plants representing the seasonsprunus for winter, orchid for spring, bamboo for summer, and chrysanthemum for autumn. That many of the boxes were made to order, as &ts, is indicated by the inscriptions or designs. Thus a very beautiful pair of oval ink-boxes (Figure 2) was evidently a graduation present, as the fish entering the Dragon Gate is symbolic of the student's attaining his o5cial degree.
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'Present address:
Que.. Canada.
MacDanald College, MacDonald College,
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One day the antique dealer brought an ink-box (Figure 3), the surface of which had been cleaned, with the result that most of the black had been removed and
R E S P ~ ~ ~ I V E LT Y HE )S .E
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THE ONE ON THE L B IS~ INLAID ~ T CONVENTIONAL H DESIGNS. M SECOND HAS T ~ E MINIATURE E LANDSCAPE SCENES ON EACHSIDE. m~ A LATTICE DESIGNON Two oa m s Form SEASONAL PLANTS ON ITSTwo SIDES. T m Fomrra Is ALSO ONE OP A PAIRWITH B ~ R D AND PLANT DESIGNS
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the red color of metallic copper showed through. When I objected to the color the dealer explained that the black film would reappear in time, especially if the surface were rubbed with the hand. The dealer, when
CHEMICAL EDUCATION
contact with silver wire, in an open dish of sodium hydroxide over the summer. Shortly before I left China the antique dealer brought me a printed sheet, an announcement from one of the
FIGURE 2.-INK-BOXES (LENGTH 80 MM.). AN EXCEPTIONALLY BEAUTIBUL PAIROR BOXES, DESIGNED GIFT TO A PERSON WEOHASRECENTLY OBTAINEDA DEGREE. ON THE SIDES AR& THE FOURPLANTS Prunus so^ WINTER.OncnrD FOR SPRING. R ~ ~ ~ E N THE T I FOUR N C SEASONS: Bnawao am S r m r ~ eAND ~.
AS A
questioned on previous occasions, had insisted that the black color was not applied, butSwas the result of a "humour" within the pores of the metal, which had to be brought to the surface. I finally bought the box, with some misgivings, and was astonished to find that the surface became quite black within a few weeks. When a drop of ink fell upon another box on my desk, the black film instantly dissolved, exposing the red copper color. Fortunately this too turned black as before, with the passage of time. The black film is extremely thin and can easily be scratched or abraded. The insides of the boxes are ordinary copper color and do not turn black. A few experiments showed that the black substance was unaffected by heating, but was readily soluble in dilute mineral acid. It would appear to be an oxide of copper, but the nature of its formation is a mystery. Attempts to obtain information regarding the process, or to secure samples of the ore were fruitless. However, I did succeed in producing a similar glossy black iih on a strip of ordinary copper by immersing it, in
black copper manufacturers purporting to give information on the fabrication and use of Wu T'ung. I translated this, and the following is a summary of the points of interest. YOH EV-HSING'S "WU T'WG"
SHOP
1. Any design can be prodnced-flowers and grasses, human figures, birds or animals, feathers and hair; landscapes, curios; characters or quotations-all exactly according to pattern. 2. The method of manufacture is as follows. First melt ordinary copper, then add gold, sil;er, iron, tin, and so forth, and the various chemicals. Afterward hammer into a plate and then engrave grooves and inlay the silver or gold wire. This "black copper" is not produced by applying a chemical after the completion of the article. 3. If the baw is black copper, silver or gold wire is inlaid. If the base be gold or silver. a black copper pattern may be set in, and then gold or silver wire inlaid on this, if desired (Figure 1, left). 4. Upon completion the surface is red in color, and the pattern dull. Grasp the article M y in the hand, so that the perspiration may soak into the surface. Within a day or two the copper will turn black. The color is quite permanent, the pattern clear and distinot, in all, a thing of beauty. 5. Acid perspiration will prevent the formation of the black
color. I n order t o obtain a good color and bright pattern. acid. greasy, or dirty substances must not be mbbed upon the surface. But if an article has been thus damaged it may be restored by cleaning the surface with an abrasive, when the perspiration of the hand will bring hack the black color. 6. If the pattern or color is not very good, i t may be improved by abrading the surface and re-forming the black film as described above. Only genuine Wu T'ung will turn black an contact with the perspiration of the hand. Imitation articles cannot be turned black in this manner, if they have once been mbbed red.
I was not surprised to find that the fundamental secret had not been divulged: the nature of the "various chemicals" had not been revealed. But I immediately performed the following experiment. I used an abrasive to remove a portion of the black film from one of my boxes. I then held it in the palm of my hand, a t intervals, on a hot day, and within a few hours a deposit of black had been formed, with only a little of the reddish color of metallic copper showing through. At the same time there was a distinct green color of a copper compound left on my skin. Because of the apparent r81e of moisture, and the fact that i t is only the silver-inlaid surfaces that turn black. is it oossihle that there is an electrolytic reaction, with an oxide of copper being formed on the surface of that metal? It may be that the same material is found in Persia, for Janet Miller2says,
that had been expended in the execution of these articles were remarkable. The art of metal inlay is done superlatively well by the Persians and shows a high degree of technical achievement."
FIGURE 3.-INK-BOX (LENGTH 110 MM.). DATED"YUN1908." THE BOX, WHEN PURCHASED, HAD BEEN AND THE REDDISHCOLOROF METALLIC COPPER CLEANED, SHOWED T m o u o ~ . THE SURPACEBECAMEPERFECTLY BLACKWITHIN A FEWMONTHS. ON THE SIDESIS A CONVENTIONAL DESIGNOF LATTICE.BATS,PTUXUI. AND BAMBOO NAN,
I am not aware that this black copper has been described before. Its beauty, together with the interesting chemical problem of its production, renders it worthy of a wider acauaintancea
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a This black alloy of comer would amear to be similar to that described by A. J. HOPKINS,("~lcbemiichild of Greek philosoa sewet process of inlaying with a black metal composition. I t phy," ColumbiaUniveriity Pres. X\'ew York City, 1934) which was v e n dective on the white silver. The skill and ~ a t i e n c e r a z used hy the Egyptians a i the hasi.; for thcir slrhemiral proceacrs. This allov of comer. tin. lead. nod iron was black on the 'MILLER, J., "Camel bells of Baghdad," Houghton MiWin surface. Is thisevidedck a i a connection between ancient E -. m.~ t Co.. Boston and New York City. 1934, p. 208. and China?
"We were shown candlesticks and Koran-boxes decorated by
