ON COPYING BRONZE STATUETTES
Ann H. Allison, & Robert B. Pond
3 EVALUATION OF PROBABLE COPY WORK
THE INFORMATION in the preceding sections was applied to an actual art historical case, to duplicates of a model by the Italian Renaissance sculptor Antico (c. 1460–1528). The question asked was whether the duplicates of one of Antico's motifs for statuettes were from the same mold or model or were casts taken from bronze models. If the latter were found to be true, at what removal from the autograph bronze (that is, a bronze whose modeling and casting were performed by the artist himself) are the copies? This information, obtained by the IM (Internal Measurement) method to be explained be low, permits the formation of a genealogical tree whose root is the original wax model bythe artist. Except for selected data which further clarify the stylistic characteristics of a bronze by Antico and the relationship of the bronzes to him or to his shop, a more complete art historical and technical discussion of each object has not been considered relevant to the purposes of this article.
In the determination of relative sizes of duplicate bronzes simple measurements of height have not proved reliable as they can be altered before and after casting. The IM method uses other external measurements, here called internal measurements, which are taken with a caliper. Internal measurements are those of the length, width, and depth of various parts of a statuette. The locations or stations of the parts selected for these measurements were those which are considered to be least subject to change. These stations are standardized so that they can be duplicated for each specimen of the series. As the amount a cast from another bronze shrinks is small, as many as thirty measurements are taken of each statuette in order to have a sufficiency of data. In the final analysis, with increased knowledge of the technical aspects of the bronzes studies, questionable stations are eliminated. For instance, in the case of Antico, radiography has shown that his procedure frequently involved the joining of cored limbs in the final wax model. Consequently, those stations in which this might prove to be the case were deleted. During the course of the study it was observed that measurements of length and of the head are somewhat less reliable than those of width and depth and that an ideal study should include as many of the latter types as possible. Those of length can be affected by cumulative “events” of each casting process, while the head frequently has a wall thickness appreciably differing from that of the body, thereby altering the amount of shrinkage. If the neck becomes blocked, the dimensions of the head will change due to deformation shrinkage.
The raw measurements at each station for a series of three statuettes of Young Hercules are given in Table II. In Table III these measurements are arbitrarily converted into decreasing multiples of 1.25% from that of the largest measurement at each station, so that 1 equals the standard, 2 equals 1.25%, 3 equals 2.5%, and so on. Where measurements are halfway or less between percentages, the lower multiple is chosen. In Table IV these measurements are compared on a statistical basis. As it cannot be expected that all dimensions of a bronze will correspond exactly to those of another bronze, even those of the same edition, the percentage a bronze is removed from the largest member of the series at one-half or more of the measurements is taken to be the relative size index. A line has been drawn under this number. At this point in the procedure, in order to obtain additional confirmation of the results, Table III is reviewed to ascertain which types of stations contributed to these indices. When there are more than two members of a series, a statistical comparison is made using successively smaller specimens as standards for the remainder of the series, ending with pair comparisons of each member which has not yet been directly compared. These pair comparisons in longer series involving bronzes which vary more than those illustrated here may yield unsuspected relationships between its members. The statistical results of a comparison of this type are shown in Table IV-B.
Table II Young Hercules: Internal measurements in cm. for each station; 1, w, d = length, width, depth.
Table III Young Hercules: Extent of removal from large measurement at each station—in multiples of 1.25%
Table IV Young Hercules: Statistical compilation illustrating the number of stations displaying the relative shrinkage positions in Table III
To determine whether a bronze was cast from another bronze, the average shrinkage for both red-pink and yellow alloys (discussed earlier) are taken as standards. For those bronzes cast in reddish to pink alloys a midrange shrinkage of 2.5% is used, for those in yellow alloys, 3.18%. In general, and when the alloy color is in doubt, the data is interpreted broadly. Using the results of the data gathered, a genealogical chart of a series of bronzes may be formed as in Table V.
Table V Young Hercules: Genealogical Chart