Technical Examination of Oriental Lacquer - ACS Publications

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19 Technical Examination of Oriental Lacquer GARY W . C A R R I V E A U Detroit Institute of Arts and Wayne State University, Detroit, MI 48202

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Technical

examination of objects coated with a

protective

covering derived from the sap of a shrubby tree

produces

information

materials

that can be used to determine

and methods of manufacture.

the

This information

sometimes

indicates when and where the piece was made. This chapter is intended

to present a brief review of the raw

urushi, and the history and study of its use. techniques

have included atomic absorption

thin layer chromatography, emission spectroscopy, scanning

electron

are reviewed. cluding

microscopy;

IR

analysis,

and optical and

these methods and

results

new methods are reported,

the use of energy dispensive

nondestructive

spectroscopy,

thermal

x-ray radiography,

In addition,

scanning photoacoustical

T

differential

material Analytical

x-ray

in-

fluorescence,

microscopy, laser microprobe

and

spectrophotometry.

H E SAP O F A S H R U B B Y T R E E growing over large areas of Asia has been used to produce a highly durable protective and decorative coating

for a wide variety of objects. T h e finished material, called lacquer, is known to have been used for over 3700 years. It is seen on utilitarian everyday objects such as boxes, trays, and cups, and further serves as a protective and decorative coating on furniture, armor, masks, and sculpture. Furthermore, lacquer ware continues to be used and remains highly

prized even today. T h e methods of collecting and refining the raw materials and the production of objects are very labor intensive. E v e n before the final decoration is applied, the manufacture of high-quality lacquer ware i n volves up to 30 different processes. These include steps i n preparation and stabilization of the inner core, application of an undercoating to reinforce the core, and application of the intermediate lacquer layers, each polished and prepared for final decoration. These last decorative procedures may require a great number of multiple layers incorporating a variety of materials. 0065-2393/84/0205-0395$06.00/0 © 1984 American Chemical Society

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The unique qualities of lacquer ware fully justify this effort. Once hardened, the lacquer surface protects from dampness and mold; is relatively scratchproof; and remains unaffected by alcohol, hot water, salt, and alkali solutions. E v e n with everyday use (employing proper care), lacquered objects can survive in an excellent state for a very long time. This chapter presents a brief review of the raw material and the history and study of its uses. Technical examination, through the use of a variety of scientific methods, has provided information about the raw material and the film hardening process. Certain diagnostic measurements were used to determine the raw material source (where the trees

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were grown) and the age of lacquer objects. A n extended bibliography is included for those wishing additional details.

Raw Material Oriental lacquer is produced from the sap of a tree, Rhus vernicifera, grown over wide areas of C h i n a , Japan, Korea, and other Southeast Asian countries. T h e evolution of lacquer has been lost in history, but we know that lacquer was used before the Shang dynasty (1751-1112 B.c.) in China. It was employed both in writing and as a protective coating. D u r i n g the C h o u dynasty (1111-256 B.C.), the lacquer craft developed but because of the limited production, most lacquer objects were reserved for royalty and the nobility. In Japan, the earliest known objects are thought to have been produced between the third century B.c. and the fourth century A . D . There is no common agreement among scholars on whether the tree that produces urushi is indigenous to Japan or if it was introduced from C h i n a . However although the subject matter and style of early Japanese lacquer were first influenced by the neighboring Chinese, the Japanese evolved a different tradition, both stylistically and in manufacture methods.

Use of Lacquer Lacquer differs entirely from varnish and lac, although the terms may be mistakenly interchanged i n the literature. Varnish is a natural resin dissolved in a solvent. After the solution has been applied, the solvent volatilizes, leaving a shiny glaze. L a c is the deposit of the Coccus lacca insect, which is collected from certain trees in East India. This deposit is refined and dissolved in a solvent. Both varnish and lac coatings are much less stable than the coating found on oriental lacquer ware. Raw lacquer is called urushi. F o r our knowledge of the composition of urushi and the complex hardening process of the thin film layers, we now rely primarily on the recent work of Kumanotani and his coworkers (1-7). T h e sap of the Japanese lacquer tree is a latex containing 20-25% water, 65-70% urushic acid (urushiol), approximately 10% gummy sub-

Lambert; Archaeological Chemistry—III Advances in Chemistry; American Chemical Society: Washington, DC, 1984.

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stances, and less than 1% laccase. T h e amounts vary with the type of tree, where it is grown and cut for release of sap, and the time of year the collection is made. T h e last component, laccase, is considered to be the enzyme responsible for the hardening process. Chinese lacquer is thought by some to be inferior to Japanese lacquer because it has a smaller amount of urushiol and also because the Chinese often used vegetable oils as extenders. Urushi,

although it forms a thin film in an oxidation process, is

unique in that it hardens in the presence of a high relative humidity.

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Hardening is actually accelerated with an increase in the amount of moisture present.

Lacquer will not harden perfectly at normal room

temperature and humidity conditions; a good film is only possible in a damp enclosure between 20 and 28 ° C . Many grades of urushi are used, depending on the different applications or decorative effects desired. (A detailed description of materials and methods may be found in Reference 8.) T h e sap, after removal of some water and careful filtration and cleaning, is most often coated onto a prepared core. This core is usually made of wood, but examples of leather, basketry, cloth, paper, metal, pottery, shell, horn, and fish skin may be found. Normally, many lacquer layers are built up on the core, with polishing occurring after each layer has hardened. Lacquer was probably first used solely as a protective coating; decorative elements have evolved with time. Objects may be simply colored in monochromatic red or black, for example, Chinese bowls and carved boxes. Other objects may be highly ornate, with patterns introduced by using metal flakes or foil to produce decorations on the interior subsurface layers. Some pieces may have designs of inlaid mother of pearl; still others have a combination of metal-flake patterns and mother-of-pearl inlay. It is common for some objects to have 60-100 individual layers. Hardening and polishing each layer takes from several days to months; it might require many years for completion of an article. W h e n properly produced, a lacquer film is extremely durable. It is unaffected by most acids, bases, alcohol and water at room temperatures. O n e common usage of lacquer ware is for food storage. Lacquer films are, however, sensitive to U V radiation and extremes of heat; both may cause irreversible discoloration.

History Early discussions on lacquer ware i n occidental publications are rare. A n article by Father d'Incarville in 1760 (9) appears to be one of the first containing information on lacquer composition and uses. This is followed in the late 19th century by reports by Wagener (JO), M a ë d a (11), Rein

Lambert; Archaeological Chemistry—III Advances in Chemistry; American Chemical Society: Washington, DC, 1984.

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(12), and Yoshida (13), all of which contain details on the collection, preparation, and uses of this unique material.

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Over the past hundred years numerous experimental methods have been used for the study of urushi and the finished lacquer ware. T h e first recorded reports on chemical experiments are those of Ishimatsu (14), Yoshida (13) and Korschelt and Yoshida (25). Miyama gave the name urushiol to urushic acid (16), and he and Majima and coworkers (17-26) further explored the composition of urushi. W o r k by Sunthanker, Dawson, and Symmes (27,28) helped to determine that it contained three substituted catechol derivatives containing various different side chains. The previously mentioned reports by Kumanotani and coworkers (1-7) have allowed us to understand more of the details of the raw urushi, the complex mechanism of film hardening, and some properties of the hardened layers. M o r e recent papers have recorded results from studies of the actual lacquer manufacturing methods and the decorative materials used. A brief review of selected papers follows, grouped by principal investigator. Sir Harry Garner has used emission spectroscopy and optical m i croscopy to study pigments. H e found pigments composed of mercury as H g S (cinnabar) in red colors, arsenic as A s S (orpiment) in yellow colors, and carbon in black colors from a 15th-century Chinese carved box (29). In addition, he has grouped objects according to age by the color of pigments in thin cross sections (29). 2

3

Toshikatsu Nakasato also reports on studies using optical microscopy, but he further uses x-ray radiography. H i s main emphasis has been on correlating the object's age with certain characteristics of metal flakes or foil used in decorations. H e argues that information concerning the composition, size, and shape of maki-e metal flakes can sometimes be used to determine the age and provenance of decorated objects (30-37). A n additional report on the use of x-ray radiography comes from d'Argence (38). H e studied the methods used to manufacture the wooden core on medieval Chinese lacquer bowls. Toshiko Kenjo has used perhaps the greatest number of different methods for studying materials and manufacturing methods. F o r example, IR spectrophotometry results show that some absorption bands vary in intensity and inverse wavenumber as a function of the source of the urushi and the age and hardness of the lacquer layer (39,40). Atomic absorption spectroscopy has been used to measure concentrations of copper, iron, and manganese in lacquer layers (41); Kenjo uses this information in provenance studies. Another tool for provenance investigations is the use of differential thermal analysis ( D T A ) (42,43). Kenjo has also used D T A to identify unknown thin layers as lacquer. In addition, specific gravity tests have been used to separate lacquer fragments from soil on archaeological excavations (44). Kenjo has also used thin layer

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chromatography (45) and IR spectrophotometry (46) to detect the pres­ ence of natural vegetable oil extenders such as linseed oil and yam oil. E v e n more recently, Burmester reported on the use of pyrolysis mass spectroscopy i n lacquer studies (47,48). T h e results, when used with multivariate data analysis, prove to be a helpful provenance tool. Burmester has also extended the IR work through the use of a Fourier transform instrument and, further, evaluated the efEcacy of using carbon13 N M R measurements (49).

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New Analytical Methods Finally we wish to introduce four new analytical methods for lacquer problems; three are now used i n the Detroit Institute of Arts lacquer project and the remaining method is undergoing development for lacquer use. These methods are energy dispersive x-ray fluorescence, laser m i ­ croprobe, scanning photoacoustical microscopy, and nondestructive IR spectrophotometry. T h e first method, x-ray fluorescence, has been used for many years to help solve problems of art and archaeological objects by answering questions concerning their elemental composition. T h e instrument at the Detroit Institute of Arts, a Kevex M o d e l 0750A Macroanalyzer, is entirely nondestructive (no sample need be taken) and can analyze the surface of an object having any size and shape. Elemental concentrations ranging from sodium to uranium can be detected simultaneously and the sen­ sitivity may be less than 100 p p m , depending on interferences from associated elements. Qualitative and(or) semiquantitative information from lacquer ware may be used to identify metals used i n maki-e dust, flakes or foil; to classify the pigments used to color lacquer layers; and, with the relatively high sensitivity, to determine trace-element concen­ trations. This information can be used with other data, such as those relating to style and manufacturing methods, to help answer questions of age, authenticity, provenance, and evidence of repair (52). 1

As an adjunct to x-ray fluorescence, we use the laser microprobe (53,54). This, of course, is not an entirely nondestructive technique. However, the hole that is produced has dimensions of the order of 1 0 20 μητ, not visible to the unaided eye. T h e laser microprobe serves as an important supplement to x-ray fluorescence because analysis is not limited only to the upper surface. T h e laser beam can carefully excavate to lower and lower layers by controlled repeated laser pulses. Analysis can be performed on each individual layer of interest. In addition, the

There are many excellent textbooks for x-ray fluorescence; recent examples are References 50 and 51. 1

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much higher spatial resolution of the laser microprobe enables the study of much finer details than when using x-ray

fluorescence.

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The two previous methods deal with qualitative and(or) quantitative composition studies. T h e scanning photoacoustical microscope (55-57) is used to study another facet of lacquer ware problems, that of structural stability. T h e major conservation problem with lacquer occurs when the thin layers delaminate from the core, which generally happens to objects that are allowed to undergo large variations in relative humidity in storage or display areas. Such variations can periodically shrink or expand the core, placing strains on the core-lacquer interface. O f course, physical abuse can also damage the lacquer layer. T h e unaided eye, binocular microscope, and(or) x-ray radiography have all been used to study damage and the efficacy of restoration techniques. W i t h its far greater sensitivity, absolute nondestructive nature, and ability to study objects of any size or shape, scanning photoacoustical microscopy offers improvements i n the study of damage and repair. W e have found that this technique may also be used to determine some methods of manufacture, such as the nature of raw materials and the use of fabrics to strengthen edges and corners. The final example of new instruments for lacquer analysis uses IR spectrophotometry. Kenjo has pointed out how useful IR spectra can be when used for provenance studies (39,40). M . J. D . Low, of N e w York University, has recently developed an IR instrument that is nondestructive: no sample taking or preparation is required (58,59). Use of this instrument will prove to be extremely important because of the value of some lacquer ware and the justifiable reluctance of curators to allow samples to be taken. W e are currently evaluating this new instrument's performance with lacquer.

Conclusions This discussion has been intended to provide a review of the technical study of oriental lacquer. This unique material varies greatly i n composition, methods of manufacture, and artistic style. Because of this, it offers a wide variety of exciting problems to solve. A bibliography of selected papers has been included as a guide for further study. In addition to this, a detailed annotated bibliography on technical analysis of lacquer, containing i n excess of 380 entries, will be published soon (60).

Acknowledgments W e wish to thank R. L . Thomas, L . D . Favro, P. K . K u o , D . Coleman, and M . J. D . L o w for technical and experimental assistance. W e also

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extend our thanks to S. Mitchell, L . Gorman, S. Weintraub, and B. Roberts for their encouraging and informative comments and support.

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Literature Cited 1. Kumanotani, J.; Kato, T . ; Hikosaka, A. J. Polym. Sci., Part C 1968, 23, 51931 2. Kumanotani, J. Proc. FATIPEC Congr. 13th, Cannes 1976, 360-69 3. Kumanotani, J. Macromol. Sci. Chem, 1978, 179. 47-61 4. Kumanotani, J. Kobunshi 1979, 28, 871-73 5. Kumanotani, J.; Achiwa, O . ; Ohima, R.; Adachi, K. Proc. Int. Symp. Cult. Prop. Anal. Chem. 1979, 51-62 6. Kumanotani, J. Proc. 182nd Nat. Meet. Am. Chem. Soc., 1981. 7. Kato, T . ; Kumanotani, J. Bull. Chem. Soc. Jpn., 1969, 42, 2375. 8. Jahss, M . ; Jahss, B. "Inro, and Other Miniature Forms of Japanese Lacquer Art"; Tuttle: Rutland, Vt., 1971; Chap III. 9. d'Incarvelle, Fr. "Mémoirs de Mathématique et la Physique", Vol. III. 1760; pp. 117-42. A free German translation is found in Watins, M . "Kunst des Staffiermalers, Vergolders, Lackiers and Farbenfabrikanten"; Nuer Schauplatz der Kunst und Harkwerke: Ilmenau, Germany 1824. 10. Wagener, G . Dinglers Polytech. J. 1875, 218, 361. 11. Maëda, . Rev. Sci. 1878, 7, 117-28. 12. Rein, J. Oesterr. Monatsschr. Orient 1882, 4,5. 13. Yoshida, H . J. Chem. Soc. 1883, 472. 14. Ishimatsu, S. Mem. Manchester Lit. Philos. Soc. 1882, 3, Ser. 7. 15. Korschelt, O . ; Yoshida, H . Trans. Asiatic Soc. Jpn, 1885, 12, 180-220. 16. Miyama, K. J. Coll. Eng. (Tokyo) 1908, 4, 89. 17. Majima, R. Cho, S. Ber. Dtsch. Chem. Ges. 1907, 40, 4390. 18. Majima, R. Ber. Dtsch. Chem. Ges. 1909, 42, 1418. 19. Ibid., 3664. 20. Ibid., 1912, 45, 2727. 21. Ibid., 1913, 46, 4080. 22. Ibid., 1915, 48, 1593. 23. Majima, R.; Tahara, J. Ber. Dtsch. Chem. Ges. 1915, 48, 1606. 24. Majima, R.; Takayama, G . Ber. Dtsch. Chem. Ges. 1920, 53, 1907. 25. Majima, R. Ber. Dtsch. Chem. Ges. 1922, 55, 172. 26. Majima, R., Unter. Japanlack, Iwata Inst. Plant Chem. Tokyo, 1924. 27. Sunthanker, S. W . ; Dawson, C . J. Am. Chem. Soc. 1954, 76, 5070-74. 28. Symmes, W . ; Dawson, R. J. Am. Chem. Soc. 1954, 76, 2959. 29. Garner, Sir Harry, Stud. Conserv. 1963, 8, 84-98. 30. Nakasato, T. Hozon Ryogaku, 1967, 3, 55-69. 31. Nakasato, T. Sci. Conserv. (Tokyo) 1972, 9, 63-77. 32. Nakasato, T. Hozon Kagaku, 1976, 15, 56-83. 33. Ibid., 1977, 16, 35-44. 34. Ibid., 1978, 17, 16-24. 35. Ibid., 1979, 18, 73-92. 36. Ibid., 1980, 19, 91-105. 37. Nakasato, T. Proc. Int. Symp. Cult. Prop. Anal. Chem. 1980, 113-24. 38. d'Argence, R. Apollo 1980, 112, 6-19. 39. Kenjo, T . Hozon Kagaku 1976, 15, 1-8. 40. Kenjo, T. Sci. Pap. Jpn. Antiq. Art Crafts 1978, 23, 32-39. 41. Kenjo, T. Int. Symp. Conserv. Restor. Cult. Prop. (Tokyo) 1978, 63-69.

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42. 43. 44. 45. 46. 47. 48. 49.

Kenjo, T . Hozon Kagaku 1980, 19, 15-19. Sato, M . Shikizai Kyokaishi 1969, 42, 118. Kenjo, T . Hozon Kagaku 1978, 17, 6-10. Ibid., 1973, 11, 91-93. Ibid., 1977, 16, 12-16. Burmester, Α.; Brandt, K. Berlin. Beitr. Archaeom. 1982, 7. Burmester, A. Archaeometry 1983, 25 (1), 45-58. Burmester, A. Proc. 22nd Symp. on Archaeometry, Bradford, 1982, 18493. Jenkins, R.; Gould, R.; Gedcke, D . "Quantitative X-ray Spectrometry"; Dekker: New York, 1981. Tertian, R; Claisse, F. "Principles of Quantitative X-Ray Fluorescence Analysis"; Heyden: London, 1982. Carriveau, G . W . "Technical Examination of Lacquer Using X-ray Fluororescence"; in press. Breck, F . ; Young, W . J. In "Application of Science to Works of Art"; Young, W. J., E d . ; Boston Museum of Fine Arts: Boston, 1967. van Deijck, W . ; Balke, J.; Maessen, F. Spectrochim. Acta, Part Β 1979, 34, 359-69. Wong, Y. H.; Thomas, R. L.; Hawkins, G . Appl. Phys. Lett. 1978, 32, 53839 Thomas, R. L . ; Pouch, J. J.; Wong, Y. H.; Favro, L . D . ; Kuo, P. K . ; Rosencwaig, Α., J. Appl. Phys. 1980, 51, 1152-56. Pouch, J. J.; Thomas, R. L.; Wong, Y. H . J. Opt. Soc. Am. 1980, 70, 56264. Low, M . J. D . ; Lacroix, M . ; Moterra, C . ; Severdia, A . G . Am. Lab., 1982, 14, 16-27. Low, M . J. D . ; Lacroix, M . ; Moterra, C . Appl. Spectrosc. 1982, 36, 58284. Carriveau, G . W . ; Caldwell, R. " A n Annotated Bibliography on the Tech­ nical Analysis of Oriental Lacquer"; in press.

50.

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51. 52. 53. 54. 55. 56. 57. 58. 59. 60.

R E C E I V E D for review November 3, 1982. A C C E P T E D for publication May 16, 1983.

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