Petrological and geochemical study of three pieces of sculpture in the collection of M. A .Mansoor and sons

Leon T. Silver

INTRODUCTION

On January 20,1959, Mr. William Mansoor presented himself at my office. He introduced himself as a dealer of Egyptian antiquities and displayed three small but striking pieces of sculpture. He stated that these specimens belonged to his father, head of the firm of M. A. Mansoor and Sons, formerly of Shepheard's Hotel in Cairo, Egypt. The specimens are believed by the owner to come from a sculptor's studio in Tel- El - Amarna in Upper Egypt and to represent works of the 18 th dynasty.

Mr. William Mansoor summarized a lengthy history of controversy over the authenticity of these pieces of antiquities. Apparently Egyptologists and "experts " on the chemistry of ancient artifacts have not been in complete agreement on whether these specimens, representing a group of more than 100 pieces, are genuinely ancient.

At Mr. Mansoor 's request, I agreed to examine the three pieces he carried, pointing out that I could make observations only on the original character of the stone and possible mineral and chemical modifications to the stone which might provide evidence on the relative age of the sculptures. Mr. Mansoor left with me, or shortly thereafter provided to me, the following reports:

  1. A history of the acquisition and disposal ( in part ) of a collection of stone sculptures from Tel-El-Amarna by M. A. Mansoor -- prepared by William Mansoor at the end of January, 1959.
  2. Report of examination by Mr. W. J. Young, Boston Museum of Fine Arts, April 14,1949. This report classed the nine objects examined by Mr. Young as forgeries.
  3. Report of examination of 66 pieces from the Mansoor collection by Zahira Mustafa and Zaki Iskandar, November 28, 1950. This included a summary of a report made by the late A. Lucas of the Cairo Museum in 1942. Both reports concluded that specimens examined by the authors were genuine antiquities.
  4. Report of examination of 13 specimens by Dr. Robert Compton, 1958. This report was favorable to their authenticity.

OBSERVATIONS

Three specimens were provided for examination:

142. A head of a young woman or youth, 5 1/2" x 3" x 2-3/4", characterized by an unusually elongated but graceful cranium. Alleged to be a daughter of Akhnaton, and sculptured in a yellowish-gray, slightly mottled, foraminiferal limestone.

144. A bas-relief plaque, displaying a youthful head, 6-3/4" x 4 1/2" x 1". The sculpture is in the same type of stone as # 142 and has a relief of less than one fourth of an inch. The subject, bearing a distinct stylistic resemblance to the head of # 142, is believed to be Akhnaton.

X-12. Head of a young man adorned by an unusual crown, 5-3/4" x 4" x 2 1/4", sculptured in a pink-buff to pink-brown, mottled foraminiferal limestone. Subject is believed to have been Akhnaton.

The following examinations were made:

(a) Binocular microscope examinations of all surface characteristics of all specimens.

(b) Petrographic examination of two principal lithologic phases of the stone of # 144.

(c) Petrographic examination of the surface character of the stone in # 144.

(d) Spectrographic comparison of trace elements in the surface material and interior material of # 144.

(e) Insoluble residue study of the surface and interior materials of # 144.

(f ) Ultra-violet light examinations of all three specimens.

STONE

The stones of specimens # 142 and # 144 are essentially identical and will be treated as such in the following discussion. It is a distinct yellowish-gray foraminiferal limestone, inhomogeneous in texture and color.

The predominant texture is found in areas more yellowish in color and consists of approximately 30 percent crystalline foraminiferal tests in a very fine-grained calcite matrix. The tests vary in size from 0.05 to 0.25 mm, show excellent microarchitecture and show a diversity in species. They are relatively coarsely crystalline compared to the carbonate in the matrix which has individual grains generally much less than 0.01 mm in diameter.

The less common texture is found in areas grayish in color. Here the tests make up only 5 to 10 percent of the texture and the remaining material is light-gray carbonate matrix similar to, but even finer grained than, the matrix in the more yellow portion of the stone. The basic yellow coloring agent in the stone is limonite, hydrated ferric oxide, which seems to be most concentrated in the inner parts of the foraminifera. As the abundance of the latter goes down, so the yellow color grades to the more grayish color of the matrix. Even the matrix of the foraminifera-rich texture is yellow-stained, however.

Petrographically, the most significant element in the texture is the extension of delicate foraminiferal tests across the boundaries between yellow and gray material with no disturbance. This gray material is clearly not an artificial paste additive to the stone. In grosser structure it can be seen that the yellow and gray mottling is parallel to the original bedding. The gray minor masses apparently originated as fine-grained carbonate mud clots in the original foraminiferal ooze.

The pinkish stone of #X-12 appears to be entirely similar in texture to #142 and #144, from binocular examination. The same two basic textural types are present. The more coarse material is pinkish brown while the finer-grained, foraminifera-poor material in pinkish buff. The pink color appears to reflect limonite and hematitie concentrations inside the foraminiferal tests. In addition there is a wide range of concentration of iron oxides in the coarser matrix producing a considerable mottling which also appears to be bedding controlled.

All of the stones display some degree of natural fracturing partly to completely healed by carbonate and by a few other minerals. In specimen #142, these fractures are commonly the locus of minute limonite pseudomorphs (possibly after some former well-crystallized sulfide mineral) and manganese oxides. In specimen #144 only manganese oxides were developed along with carbonate in the fractures. In # X-12, the fractures are not prominent. In summary, these are natural fractures, cutting both textural types in the stone and further testimony to the completely natural character of the stone material.

SURFACES

The surfaces of the pieces may be divided into the sculptured surfaces and the irregularly fractured surfaces.

The sculptured surfaces were apparently finished with some sort of loose abrasive which left patterns of subparallel, fine lines on the surface. These lines or grooves are approximately 0.1 mm in width and about the same size as the foraminiferal tests.

The foraminifera are now etched into relief on the sculptured surfaces, standing 0.02 to 0.05mm above the matrix. Examination at 80 magnification reveals no evidence of mechanical grinding or polishing on the glossy surfaces of their tests. Even within the grooves mentioned above some tests are etched out without apparent mechanical disturbance.

Almost all of the irregular fracture surfaces show an etched quality similar to that of the sculptured surfaces. Only the grooves are missing in some places. This strongly suggests that all of the surfaces are of the same age.

A faint glossy patina appears with some irregularity both on the foraminiferal tests and on the matrix of the three specimens. Some of it may be due to handling, but its occurrence in recesses not accessible to the hands suggest another source. It occurs on almost all surfaces, both sculptured and fractured.

A special thin-section slice across the original surface of piece # 144 was prepared for the purpose of observing the marginal patina or any suggestion of a profile of weathering. A very thin dark zone, irregular in thickness but generally less than 0.01 mm, appears at the surface. From this film a faint shadowy impregnation grades into normal limestone within less than 0.05 mm. The film and the shadow apparently represent the patina sampled for the chemical studies reported below. Unfortunately, the only physical properties besides its extent which may be described are the color, dark gray to light gray, and opaqueness which is moderate to negligible. The latter is modified by the variable presence of the original translucent carbonate material. The following two points are worth noting.

  1. The patina is about equally developed on both the yellow and gray portions of the stone.
  2. The patina has permeated even the innermost parts of the minute foraminifera, indicating a very pervasive mechanism of formation.

Manganese oxides form delicate fern-like dendrites on the surfaces of specimens # 142 and # 144. Most (but not all) of the dendrites are localized along the previously mentioned fractures which carry the manganese oxide into the rock. Careful examination of a number of these dendrites indicates that there has been a definite expansion and efflorescence of manganese at the surface of the sculptured parts of these pieces.

CHEMISTRY

On specimen # 144, four samples were taken for purposes of comparing the chemistry of the surface and the interior limestone. Surface samples were taken of both the gray and yellow materials on an old fracture surface by very shallow scrapings of the patina. The same materials were sampled internally along a fresh sawcut from which material had previously been removed for petrographic examination. Table I is a comparison of analyses by emission spectroscopy normalized against a series of well established standards for analysis of carbonate rocks. Calcium oxide and carbonate are not reported and make up most of each sample.

From this table the following conclusions may be drawn:

  1. The samples have the composition of typical impure limestones with the yellow part being somewhat higher in Fe2 O3 and MgO than the gray part.
  2. The interior and the surfaces are generally similar with one exception which is believed to be significant. The MnO content increases from 0.018% to 0.032% on the gray surface, and from 0.024 % to 0.029 % on the yellow surface. This is despite the dilution nature of the surface sampling. The surface scrapings includemore than just the patina and the contribution of the surface is diluted in thesevalues. In the characteristic natural desert rock patina, the so-called "desert varnish," it has been shown that manganese oxides are invariably enriched more than most other elements. This enrichment process is a very slow one whose precise rate or mechanism is not known, but geologists consider this a reliable indicator of ancient weathered surfaces. (see article by C.G. Engel and R. P. Sharp, "Chemical Data on Desert Varnish," Bull. Geol. Soc. America, Vol. 69, pp.487-518, 1958.)

    3. Table I

    Some Major Constituents in Stone # 144

    (Values in wt. % )

    Gray Stone

    (Interior)

    Gray Stone

    (Surface)

    Yellow Stone

    (Interior)

    Yellow Stone

    (Surface
    MnO 0.018 ± 0.002 0.032 ± 0.001 0.024 ± 0.004 0.029 ± 0.001
    Fe2O3 0.58 ± 0.02 0.64 ± 0.03 1.9 ± 0.1 1.9 ± 0.01
    A12O3 0.81 ± 0.09 0.70 ± 0.02 1.14 ± 0.04 0.75 ± 0.03
    SiO2 13. ± 1. 11. ± 1. 13. ± 1. 13. ± 1.
    MgO 1.3 ± 0.1 1.1 ± 0.1 4. ± 0.5 4. ± 0.5
    TiO2 0.040 ± 0.003 0.041 ± 0.002 0.050 ± 0.005 0.044 ± 0.003

    In addition to the elements listed in Table I, a general spectrographic survey of trace element concentrations in the same samples were made. Only two significant enrichments appeared in the surface materials and they are given in Table II.

    Table II (parts per million*)

    Gray Stone

    (interior)

    Yellow Stone

    (surface)

    Gray Stone

    (interior)

    Yellow Stone

    (surface)
    Barium

    64

    90

    64

    120
    Copper

    24

    110

    38

    80

    *Accuracy of method: ± 20 % of figure shown.

    Engel and Sharp in their authoritative study of desert varnish list these two trace elements among those showing greatest enrichment in the varnish. It is possible therefore to find in this trace element data some additional support for the development of an incipient desert varnish.

    Two other types of tests were performed on the specimens. From # 144, scrapings from the sculptured surface were dissolved in acid and the insoluble residues were examined in immersion oils under the microscope. These were predominantly very fine grains of quartz and feldspar, a perfectly reasonable constituent in this rock. The purpose of this examination was to look for imbedded particles of modern, artificial abrasives. The results were negative.

    All three specimens were examined in ultra violet light, both long (3660 Ao) and short (2537 Ao) wavelengths, and compared with other fine grained limestones having both geologically weathered and fresh surfaces. No convincing criteria were developed which might apply to determination of the age of the surface. These results were also considered negative.

    CONCLUSIONS AND OPINIONS

    1. All of the material in the sculptured pieces is natural stone. There are small quantities of surface deposits which appear secondary and perhaps artificial, but these are not related in any apparent way to an attempt to falsify the surface. There is no evidence of a false paste medium applied to the specimens as has been implied by at least one previous examiner.
    2. Ultra-violet fluorescence examinations provid e no unique tests of authenticity for these samples. Their response is compl etely compatible with that of naturally weathered limestones, modified very slightly by some secondary contamination by handlers at undetermined times. The basic theory of ultra-violet fluorescence in carbonates is not sufficiently well-established to accept generalizations for all limestones and marbles.
    3. The manganese grains which are clearly within the stone do locally develop surficial dendritic efflorescences which expand on the surface and are younger than the sculptured surface. This is suggestive of considerable age and exposure to migrating waters.
    4. The surface patina while thin is widespread in area and distinctly pervasive with a transition zone extending well into the limestone.
    5. Sampling and analysis of two phases of the limestone, each represented internally and surficially in # 144, indicates the surface patina is enriched perceptibly in manganese oxide, barium and copper despite the fact that the sampling method tends to minimize the apparent differences. The enrichments are characteristic of enrichments observed in the development of desert varnish on desert rocks as reported in the most comprehensive and modern study of desert varnish chemistry to date (see the reference cited). Alt hough the presence of manganese oxide in desert varnish has long been known, the enrichments in the trace elements barium and copper were first reported in 1958, long after the first appearance of the Mansoor collection. Their presence in a false patina would indeed be highly fortuitous.
    6. Neither in the chemical analyses nor in the solids extracted near the surface was there any evidence of materials incompatible with a primitively worked surface of ancient age.
    7. The delicate etching of the surface and the distribution of the patina, in my opinion based on experience with etching of rock surfaces, is best explained by a natural origin.
    8. The sum of the evidence from this limited examination suggests that these are genuine antiquities. Several of the methods which have been applied would provide a more definitive test if extended to increased sampling. This was not possible with the time or materials at hand. Potentially the trace element methods described, if properly handled , may be more informative than any other chemical tests applied to date.

      9. Leon T. Silver
      March 27, 1959
      Pasadena, California

         Mail Address :

                                   Professor Leon T. Silver
                                   Geochemistry Laboratory
                                   Division of Geological Sciences
                                   California Institute of Technology
                                   Pasadena 4, California
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