Archaeological ChemistryâII - ACS Publications - American Chemical

5 Applications of X-Ray Radiography in the Study of Archaeological Objects PIETER MEYERS

Downloaded by CORNELL UNIV on October 18, 2016 | http://pubs.acs.org Publication Date: June 1, 1978 | doi: 10.1021/ba-1978-0171.ch005

Research Laboratory, The Metropolitan Museum of Art, New York NY 10028 Although the use of X-ray radiography in the study of paintings is well known, its application to other museum objects has been more limited. However, X-ray radiography of several museum objects provided new, useful information: a ceramic bowl is composed of unrelated fragments and plaster; there is a clay core in a bronze figurine from ca. 2500 B.C.; and the famous Bronze Horse was cast by the lost wax process and not, as had been suggested, by a modern piece-mold sand casting process. In addition, X-ray radiography helped to provide details on the methods of manufactuer of Sasanian silver and a Chinese bronze vessel. H p h e use of x-ray radiography to study art objects began when German scientists produced the first x-ray radiographs of paintings soon after the discovery of x-rays by Roentgen in 1895. During the next half century this became a standard technique for examining paintings i n many museum laboratories ( J ) , although its further development i n Germany was apparently hampered by a patent on the radiography of paintings (2). Since then the usefulness and limitations of the technique have been clearly established. Systematic studies of x-ray radiographs provided much important information on the painting techniques of individuals and schools of artists. Today most of the important paintings i n museum collections have been radiographed, and the published literature contains hundreds of articles dealing with radiographic studies of paintings. Conservators as well as museum curators and art historians make frequent use of x-ray radiographs, which often can be interpreted straightforwardly by the trained eye. Furthermore, the necessary equipment is readily available and relatively simple to use. In contrast, the application of x-ray radiography to archaeological materials and other three-dimensional objects has not reached the same level of sophistication. The reasons seem obvious: the more powerful 0-8412-0397-0/78/33-171-079$05.00/l © 1978 American Chemical Society

Carter; Archaeological Chemistry—II Advances in Chemistry; American Chemical Society: Washington, DC, 1978.


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equipment necessary for radiography of most three-dimensional objects is not readily available; the greater complexity of the actual process and of the subsequent interpretation of the radiographic images may have discouraged potential investigators; fewer scholars have realized the utility of such investigations for studies of ancient technologies. The wider application of x-ray radiography to archaeological materials also is perhaps being prevented by the scarcity i n the literature of comparative material. Proper descriptions of radiographic studies are needed to provide detailed information on specific aspects of the development of ancient technology. This chapter was written i n the hope that more extensive discussion of the techniques and results of applying x-ray radiography to archaeological artifacts w i l l increase interest i n and contribute to the success of current and future projects. Methods Although x-ray radiography equipment used for paintings is sometimes suitable for the study of objects made of wood, ivory, bone, or other organic materials and for some ceramics, most three-dimensional objects require more powerful equipment. Industrial x-ray radiography units with a maximum x-ray energy of 200-300 k V are required for most metal and stone artifacts and for large ceramics. The principles of x-ray radiography need not be elaborated in detail; the theory is well known, and the practical aspects are fully described i n the literature (3). However, i n museum laboratories radiography is frequently performed by personnel not necessarily familiar with the various practical aspects. E v e n though the available equipment restricts the choice of conditions for radiography, the operator must make a number of decisions that can seriously affect the success of the project. It may be of use, therefore, to list some of the variables encountered i n x-ray radiography. High Voltage or Maximum X-Ray Energy. Optimum conditions are determined by the thickness of the object to be radiographed and by the atomic numbers of the elements of which it is composed. The kilovoltage must be high enough to allow a sufficient amount of x-ray radiation to penetrate the object. Since the contrast in the radiographic image decreases with increasing x-ray energy, the kilovoltage must not be too high. X-Ray Film. The best x-ray films have very fine grain, such as Kodak type M . These give the highest resolution, but they require longer exposure time than the larger grained films. A full description of x-ray films is given in the product literature or in Bridgman's discussion of x-ray films (4). To obtain high quality radiographs it is essential to follow accurately the manufacturers film processing directions.



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Intensifying Screens and Lead Screens. Chemical intensifying screens may shorten exposure times by factors up to 200; however their use is not recommended because they decrease resolution. Lead screens, on the other hand, serve dual purposes: they not only absorb a large amount of unwanted secondary radiation, but they also act as intensifying screens because secondary electrons are emitted by the lead upon impact of x-rays. Such screens, 0.005 in. thick, should be placed on either side of the film when exposures greater than 150 kV are used. Filters. Metal filters placed near the exit window of the x-ray tube reduce the low energy x-rays emitted at the anode. Their use will reduce the contrast but will improve the resolution. Image Registration. The standard method of observing x-ray images is through the use of x-ray film. Other methods of registering radiographic impressions includefluoroscopy,xeroradiography, and color radiography. Fluoroscopy involves the projection of the radiographic image on a fluorescent screen which can be viewed directly or can be photographed. The resolution is inferior to that of the standard film radiography. In xeroradiography the radiographic image is recorded on an electrically charged plate. Resolution and contrast in prints obtained from these plates compare favorably with those in standard film radiographs. Xeroradiography has not been widely used yet in studies of archaeological objects (5). Color radiography appeared to be a promising technique approximately 10 years ago (6,7), but since the literature describes no recent applications, it may be assumed that this technique did not live up to its initial promise. Microradiography has not yet been used extensively to study archaeological materials. This technique, which allows study of details too fine to be seen with the naked eye by enlarging the x-ray radiograph, may find useful applications in the future. Stereoradiography permits the study of a very informative threedimensional radiographic image by a simple but effective method. Two radiographs are obtained under identical conditions except that the x-ray target is moved 4 in. (the distance between the human eyes) parallel to the film between the first and second exposures. Then, by a simple mirror system the radiographs are viewed in such a way that each eye sees only one film. The superimposed images give the impression of a three-dimensional radiograph. A good radiograph obtained by one of the methods described provides an accurate and lasting record of the object under study. When duplicates or prints are produced much information is lost, especially in the processing of prints. Most photographic films cannot accommodate the large range of densities typical for x-ray radiographs. Methods of reproducing radiographs have been summarized by White (8).


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Applications


Among the objects most susceptible to successful radiographic study are those with well-defined internal structures such as cast bronzes, jewelry, furniture, musical instruments, and ceramics. The variety of materials that have been studied is described in the literature. For example Bridgman reported on the radiography of museum objects (9), Gettens examined Chinese bronzes (10), Gorelick studied cylinder seals (II), Bertrand et al. and Gugel et al. described applications to ceramics (12,13), and Harris and Weeks radiographed mummies of ancient Egyptian royalty (14). Most publications discuss x-ray radiography of only a few threedimensional objects and deal with specific aspects of these such as method of manufacture or repairs and hidden decorations. The few radiographic studies where methods of manufacture have been studied on a systematic basis using large groups of objects have been very successful. The radiographic study of Chinese bronzes by Gettens (10) contributed significantly to a better understanding of Chinese bronze casting techniques. An investigation at The Metropolitan Museum of Art of Renaissance bronzes enabled R. E. Stone to correlate casting characteristics observed in x-ray radiographs with workshops of master sculptors such as Antico,

Figure 1. Glazed Minai ware bowl, 12-13th century A.D., Persian. The Metropolitan Museum of Art, Acc. # 57.36.11.



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Riccio, and Seyero (15). In addition, the x-ray evidence made possible a detailed reconstruction of the casting processes and allowed proper attribution of several Renaissance bronzes previously unattributed or erroneously ascribed. The following sections present some examples of x-ray radiographic studies. A l l the x-ray radiographs illustrating this discussion were made with a Norelco 300 M G industrial x-ray unit on Kodak industrial x-ray film type M encased i n 0.005-in. lead screens, unless otherwise indicated. Islamic Ceramic B o w l . X-ray investigation can help solve the common problem of how much of an apparently complete ceramic vessel is original and how much is restoration. Several Islamic glazed M i n a i bowls of the 12th and 13th centuries A . D . presented such a problem; examination with U V light indicated that large areas were overpainted and apparently restored. W h e n x-ray radiographs were obtained, it became evident that among the 15 objects examined, more than half were composed of unrelated ceramic fragments with plaster fills. The bowl shown in Figure 1 is an example of this group. The x-ray radiograph of that bowl (Figure 2) shows clearly that the bottom part bears no relationship to the fragments making up most of the rest of the bowl. Areas between these fragments, slightly darker i n color, are plaster fills. Another bowl from this group has been described by Pease (16).

Figure 2. X-ray radiograph of howl shown in Figure 1. The bowl is assembled from fragments of two unrelated vessels as indicated by the differences in density and in structure. Exposure: 50 kV, 5 mA, recorded on Kodak No-Screen film.



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Sasanian Silver. The subject of Sasanian silver was well represented in a previous symposium (17,18,19). Articles presented at this meeting dealt predominantly with elemental compositions. In a general technical study on Sasanian silver objects at the Research Laboratory of the Metropolitan Museum of Art, considerable attention has been given to the methods of manufacture. Careful observations using a binocular microscope, measurements of the thickness of the metal walls, and especially x-ray radiography of a large number of Sasanian silver vessels resulted i n a well defined theory of the practices of the Sasanian silversmith. The findings of this study, which are entirely consistent with other evidence, w i l l be reported in detail elsewhere, but some conclusions are listed here. As shown below, the investigation produced disagreement with the widely accepted theory based on statements by Orbeli and Trevers (20) that the Sasanian silversmith used three basically different techniques to produce plates and bowls. H A M M E R I N G . The plate or bowl was shaped by hammering from a cast blank. The interior of the plates or exterior of the bowls was decorated by chasing or engraving. W h e n decoration in relief was required, the background was carved away around the figures (Figure 4 ) ; to produce high-relief decoration pre-cast and pre-hammered pieces were added to the plate, as shown i n the plate illustrated i n Ref. 18. CASTING. D O U B L E S H E L L T E C H N I Q U E . Plates were constructed of a hammered undecorated exterior plate and a hammered interior plate with a repousse decoration. The two were secured together either by soldering or by bending the edges of the exterior plate inward and hammering them down over the interior plate.

In general x-ray radiographs consistently show characteristics indicating the method of manufacture. For example cast plates and bowls invariably contain trapped gas or voids i n the metal, which appear i n radiographs as dark spots (Figure 3); the radiographic image of a cast plate or bowl is often mottled and grainy. Frequently the wall thickness of cast objects increases i n areas of greatest curvature, supposedly to avoid contact between the inner and outer investment walls during the casting operation. Hammered plates and bowls, on the other hand, do not contain trapped gas; their radiographic images are smooth and sharp with characteristic density changes caused by the hammering. W a l l thickness decreases as a result of the more extensive hammering needed to produce curved surfaces. Plates or bowls made by the double shell technique are distinguished readily from cast or hammered objects. Their x-ray radiographs i n most cases show small density variations that do not conform with variations i n apparent metal thickness. Radiographs



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Figure 3. X-ray radiograph of a cast plate. Irregularly distributed dark spots indicate gas trapped in the metal, a characteristic found in cast silver plates and not in hammered plates. Radiograph obtained with Philips PG 200 x-ray unit, 200 kV, 3 mA, no lead screens. of vessels produced by the double shell method should show the use of solder and the three-ring image of the bent-over r i m : two images of the outside plate with the impression of the inner plate between them. Radiographic studies on more than 100 Sasanian silver artifacts and an equal number of related silver objects strongly indicate that the Sasanian silversmith used hammering exclusively as the major shaping technique for all his objects. Among vessels accepted as genuine Sasanian, none were found that appeared to have been made b y the double shell technique or that could be positively identified as cast. The use of x-ray images to establish the method of manufacture may be illustrated by referring to a silver gilt bowl (Figures 4 and 5) originally thought to have been made by the double shell technique because many small hemispheres were visible on the inside of the bowl. These hemispheres are generally produced by punches applied on the outside; however no traces of punches appear on the outside. T h e craftsman might most simply have constructed the bowl b y using two plates, an inside one with the punched hemispheres and an outside one with a repousse* decoration of an eagle holding a gazelle. A n x-ray radiograph (Figure


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6) provides most of the evidence that this bowl was made i n an entirely different way. Silver metal was first shaped into a bowl, probably by hammering. Punches on the outside produced the hemispheres on the inside. The punch holes on the outside were then almost obliterated by shaving away the surrounding metal. The x-ray radiograph shows that the hemispheres i n the background areas are entirely solid. Small cavities

Figure 4. (top) Sasanian silver gilt bowl with eagle ana gazelle. The State Hermitage Museum, Leningrad, U.S.S.R. Figure 5. (bottom) Inside view of the silver gilt bowl shown in Figure 4.



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Figure 6.

X-ray radiograph of the silver gilt bowl shown in Figure 4. The opacity of the hemispheres (white^) indicates that the bowl is solid. The black dots visible in the center of the white circles on the eagle's raised body but not visible in the white circles in the background indicate that the hemispheres on the inside of the bowl were obtained by punches on the outside. When the outside surface was carved down to show the eagle and gazelle in low relief, polished, and decorated, the punched holes in the background disappeared completely, leaving microscopic cavities on the eagle. Radiograph obtained with Philips PG 200 x-ray unit, 200 kV, 3mA, no lead screens. still exist in the slightly thicker areas of the eagle but are visible only through a microscope. The low-relief decoration of an eagle holding a gazelle was created by carving away more silver from the background. The decoration was completed by polishing, chasing, and partial gilding. The incorrect description by Orbeli and Trever of Sasanian silversmithing techniques did not misinform the serious scholar alone; the modern forger was fooled also. Many "Sasanian" silver objects exist that were manufactured either by the double shell technique or by casting. Since our study indicated that these techniques were not used by the Sasanian silversmith, the authenticity of such objects should be considered very questionable. (Combined anomalies in style, iconography, elemental analysis, method of manufacture, and corrosion should provide, of course, the definitive evidence that these objects are not made by a Sasanian silversmith.) An authentic silver gilt plate is shown in Figure 7; its x-ray radiograph (Figure 8) is consistent with a plate shaped by hammering and




Figure 7. (top) Sasanian silver gilt plate, The State Hermitage Museum, Leningrad, U.S.S.R. Figure 8. (bottom) X-ray radiograph of Sasanian silver plate shown in Figure 7. Decorated sections appear as lighter areas indicating solid metal. This radiograph is typical for hammered Sasanian silver plates with a carved relief decoration; the light circle in the center is the radiographic impression of the foot ring. Radiograph obtained with Philips PG 200 x-ray unit, 200 kV, 3 mA, no screens.


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Figure 9. (top) Forgery of Sasanian silver gilt plate, private collection. Figure 10. (bottom) X-ray radiograph of forgery shown in Figure 9. Decorations appear as darker areas indicating hollow area between two surfaces. This plate is manufactured by the double shell technique, a method not used by Sasanian silversmiths. Exposure: 200 kV, 5 mA, lead screens.


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decorating by carving away the background around the design. A modern forgery of this plate is shown in Figure 9. The dark appearance of the decoration on the radiograph (Figure 10) indicates a hollow area between two surfaces and provides strong evidence for the double shell technique. Cast Bronzes. The greatest potential of x-ray radiography for the study of archaeological materials probably lies i n its application to cast bronzes. The following examples illustrate how certain details of bronzecasting procedures can be reconstructed based on x-ray images. C H I N E S E B R O N Z E V E S S E L . Scholars had never fully understood how the copper figures that decorate the surface of a Chinese vessel of the late C h o u dynasty (Figure 11) were applied; "inlaid" hardly appeared to be a satisfactory description. (The questions regarding the method of manufacture of this object were brought to the attention of the Metropolitan Museum of Art Research Laboratory by W . T. Chase.) Radiographs of sections of the vessel (Figure 12) provided reliable evidence for reconstructing the method of manufacture. The figures and decorations, visible on the surface of the bronze, were probably cut out of copper sheet. Attached to them are numerous square and rectangular supports. White spots on or near these supporting rods seem to indicate that they were once soldered to the copper figures. The figures with their supports were carefully placed between the inner and outer molds, with the copper figures inserted into or resting against the outer mold while the rods rested against the inner mold W h e n the molten bronze was poured into the mold, the solder melted and formed little round globules. The temperature was not high enough to obtain fusion between molten bronze of copper figures or rods. The many voids, seen as dark areas in the radiograph, were caused by rapid cooling and solidification of the bronze around the relatively cool figures and supporting rods. The vessel was then undoubtedly polished to produce a smooth surface on which the "inlays" were level with the vessel wall. A more extensive report on this method of manufacture w i l l be published elsewhere. The lost-wax process dates back to the early Bronze Age i n the ancient Near East (fourth millenium B . C . ) , but the earliest use of ceramic or clay cores i n bronze casting remains a mystery. This development in bronze casting technology is of interest because it not only saved expensive metal, but it also allowed the foundry master to produce better and more sophisticated castings. One of the earliest examples of a bronze figure cast around a ceramic core is a Sumerian statuette of an ibex (Figure 13). Its x-ray radiograph (Figure 14) indicates the sophistication of bronze casting during the middle of the third millenium B . C . The ibex was cast around a sausage-shaped ceramic core. During casting the core was held in place by two copper rods which can still be observed in the shoulder and i n the haunch. The stem of the S U M E R I A N BRONZE IBEX.



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Figure 11. Chinese Hu (ritual vessel), late Chou Dynasty, bronze with copper decoration. The Metropolitan Museum of Art,Acc. #29.100.545.

Figure 12. X-ray radiograph of section of the wall of the Hu shown in Figure 11. From the evidence seen in this radiograph—square and rectangular supports behind each figure, the white spots on or near each rod (solder), and dark areas (voids in metal) around each figure—the casting procedure described in the text can be deduced. Exposure: 275 kV, 4 mA, lead screens.



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Figure 13. Ibex on stand, arsenical copper, Sumerian, ca. 2500 B.C. The Metropolitan Museum of Art, Acc. #1974.190.

Figure 14. X-ray radiograph of ibex shown in Figure 13. The ibex is cast around a ceramic core. Two supporting metal rods are clearly visble. The stem of the superstructure extends down through the core. The head was cast separately, attached at the neck by a tongue-in-groove method and secured through a metal rod. Exposure: 300 kV, 4 mA, lead screens.


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structure above the animal's head extends through the entire core down to the outside wall of the belly. This may indicate that the ibex was cast around an already prepared superstructure.- The head was cast separately because of failure to cast the head integrally with the ibex and was attached to the neck by an ingenious tongue-in-groove method. A metal pin, faintly visible in the radiograph, secured the neck to the vertical tongue of the head. B R O N Z E H O R S E . X-ray radiography clarified the technique used to produce the much-publicized Bronze Horse (Figure 15) i n the collection of The Metropolitan Museum of A r t and thus helped to authenticate the sculpture. This object had been considered a prime example of classic Greek bronze sculpture until, in 1967, Joseph V . Noble, then Vice-Director for Administration at the Museum, declared it to be a modern forgery (22) primarily because it had been fabricated by a modern sand casting technique. This conclusion was based on a study of gamma-ray radiographs of the horse (Figure 16) and observation of a casting fin caused by a piece mold. This casting fin was described as "a line, running from the tip of his nose up through his forelock, down the mane and back, up under the belly, and all the way around." As evidence of manufacture by the sand piece-mold process, visible i n the radiograph, Noble mentioned the sand core, the iron wire running through the horse, and the ends of the transverse wires that also held the core. A n extensive technical study undertaken by the Museum's conservation department immediately after the announcement provided overwhelming evidence that the horse was not a modern forgery but was manufactured in antiquity (23,24,25). (The examination was conducted by Kate C . Lefferts, Lawrence J. Majewski, E d w a r d V . Sayre, and the author.) The most recent thermoluminescence dating tests indicate a date of manufacture in the last five centuries B . C . (26). The early stages of the technical study revealed the horse to be covered with a thick layer of black and green pigmented wax, a common treatment for bronze objects i n the 1920s and 1930s. W h e n the wax was removed, the casting fin disappeared leaving a depressed line on the face extending from a spot between the eyes to the nose. A l l experts consulted have considered this to be not a mold mark but a deliberately sculptured line. The casting fin that disappeared with the wax coating was presumably caused by piece molds made for forming a reproduction cast of the horse. The radiographic evidence strongly supports a lost-wax casting procedure and does not indicate a sand piece-mold process as demonstrated by the following observations. The iron armature is not an iron wire, as used i n modern processes, but is an irregular band, approximately 12 mm wide and 2 mm thick (Figure 17). Similar armatures and also iron chaplets have been observed i n many bronzes manufactured i n



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Figure 15 (above); Figure 16 (below). Description on opposite page.


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Figure 15. (opposite top) Bronze Horse, Hellenistic, Roman (?). The Metropolitan Museum of Art, Acc. #23.69. Figure 16. (opposite, bottom) Gamma-ray radiograph of the Bronze Horse using Ir. The modeled ceramic core, the iron armature (see also Figure 17), and the iron chaplets all indicate lost-wax casting. Density variations particularly visible in the neck area correspond to thickness variations in the metal and indicate that the artist shaved away the clay core while working on the wax model to avoid making the metal wall of the bronze figure too thin. Figure 17. (above) Gamma-ray radiograph, using Cs, of the Bronze Horse obtained by placing the film behind the horse's back. The armature, previously described as a wire, is shown to be an irregularly shaped band approximately 12 mm wide (arrows). 192

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classical antiquity. Moreover, i n modern casting procedures, armatures, chaplets, and core material are withdrawn immediately after casting. The use of iron armatures extending into three legs (the fourth leg is a cast-on ancient repair) is inconsistent with the sand casting technique; i n the wax process the legs need support, but i n the piece-mold sand casting technique, there is no need for an armature. The density variations i n the radiograph (Figure 16), particularly visible i n the area of the horse's neck, correspond to thickness variations i n the metal. They are hard to explain i n a piece-mold sand casting. In the lost-wax casting process, however, the artist may have shaved away section of the clay core to sustain reasonable wall thicknesses of his wax model. This would prevent difficulties i n the casting because of thin walls and would result i n uneven wall thicknesses. The observed density variations i n the x-ray radiograph are entirely consistent with such thickness variations. The radiographic study eliminated the most important arguments used against the authenticity of the horse. However the fact that the horse was proven to be cast with the lost-wax process d i d not automatically reestablish its authenticity. Careful visual examinations, elemental analyses, studies on corrosion products, metallurgical investigations, and various other technical studies were necessary to demonstrate that all physical characteristics of the bronze were entirely consistent


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with a date of manufacture i n antiquity. Sophisticated thermoluminescence tests on samples from the core provided the definitive evidence that the horse was produced i n classical antiquity. There is, however, still some ambiguity about the exact date of manufacture. Some scholars believe that the horse was not made during the fifth century B . C . , the originally suggested date of manufacture, but during the Hellenistic or Roman periods. A t present, thermoluminescence dating cannot distinguish between these periods, and unless these dating techniques improve, one must rely on the art historian or archaeologist for a more exact attribution.

Literature Cited 1. Burroughs, Alan, "Art Criticism from a Laboratory," Little, Brown and Co., Boston, 1938. 2. Bridgman, Charles F., Stud. Conserv. (1964) 9, 135-139. 3. Anon, "Radiography in Modern Industry," 2nd ed., Eastman Kodak Co., X-Ray Division, Rochester, 1957. 4. Bridgman, Charles F., IIC-AG Bull. (1968) 9(1), 23-94. 5. Heinemann, S., Am. Antiq. (1976) 41(1), 106-111. 6. Ryan, M. C., Mater. Eval. (1968) 26(8), 159-162. 7. Beyer, N. S., Staroba, J. S., Mater. Eval. (1968) 26(8), 167-172. 8. White, Mary Lou, ICOM Comm. For Cons., 4th Meeting, pp. 75/9/2-1 to -4 (1975). 9. Bridgman, Charles F., Expedition (1973) 15(3), 2-14. 10. Gettens, Rutherford John, "The Freer Chinese Bronzes: Volume II, Tech nical Studies," Oriental Studies, No. 7, Smithsonian Institution, Freer Gallery of Art, Washington, 1969. 11. Gorelick, L., Dent. Radiogr. Photogr. (1975) 48(1), 17-21. 12. Bertrand, A., Legrand, C., Farges, P., Bull. Soc. Fr. Ceram. (1962) 55, 45-54. 13. Gugel, E., Dichtl, H., Mitsche, R., Kupzog, E., Ber. Dtsch. Keram. Ges. (1969) 5(46), 254-259. 14. Harris, James E., Weeks, Kent R., "X-Raying the Pharaohs," Scribners, New York, 1973. 15. Stone, Richard E., private communication, unpublished data. 16. Pease, Murray, Metrop. Mus. Art Bull. (1958) 16(8), 236-240. 17. Beck, Curt W., ed., "Archaeological Chemistry," ADV. CHEM. SER. (1974) 138, 11-21. 18. Ibid., 22-33. 19. Ibid., 124-147. 20. Orbeli, G., Trevers, C., "Orfèverie Sasanide," Academie, Moscou-Leningrad, 1935. 21. Frantz, J. H., Meyers, P., unpublished data. 22. Noble, Joseph V., Metrop. Mus. Art Bull. (1968) 26(6), 253-256. 23. Lefferts, K. C., Majewski, L.J.,Sayre, E. V., Meyers, P., Metrop. Mus. J., to be published. 24. Zimmerman, D., Yuhas, M., Meyers, P., Archaeometry (1974) 16(1), 19-30. 25. Shirey, David L., The New York Times (Sunday, Dec. 24, 1972) B37. 26. Zimmerman, D., private communication. RECEIVED September 26, 1977.


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