Dirk Rieke-Zapp, AICON 3D Systems, and Elisabeth Trinkl, University of Graz   

Key words: Close range, fringe projection, cultural heritage, head vases

Introduction

 It is an ancient practice to shape a vase in human or animal form. It dates back to the early Mediterranean cultures and lasts until the modern times. In this contribution, we focus on Attic productions of pouring vases (oinochoai) of late archaic and early classical times which bodies are shaped as a human head, mostly female heads. We owe their classification to the fundamental paper of Sir John Beazley, written in 1929 [1]. Since then numerous vessels have been published, but Beazley’s groups are still relevant. Beazley categorized the vases in the form of human heads in twenty groups (Group A-W) and a miscellaneous list, according to the depicted figure and the stylistic development of the face, based on an art historic methodology. This classification grounds on a comprehensive knowledge of stylistic development and was criticized in the recent decades because of its subjectivity and lack of transparency. We focus on Beazley’s groups N and Q. The largest group of all, the Cook Class (group N), comprisesmore than 225 known vases worldwide with various human heads in which women’s heads are commonest. The small group of the Vienna Class (group Q) includesapproximately 14 samples, so far all of them are female heads. The clear majority of the Attic pottery is thrown by the potter´s wheel. Concerning the head vases the potters used the same technique only for the upper part of the vessel whereas the head of the head part of the vase was made by two molds, one for the face and a second for the rear; finally some facial details, like eyes and eyebrows, are painted by hand. The process of production interconnects head vases and terracotta figurines.

Materials and Methods

3D scan models of several vases were selected for comparison. Data was available in PLY and OBJ format and was imported in OptoCat 3D scanning and analysis software [2]. From Kunstmuseum Wien, some older scans were available in OBJ format. These scans were capturedmore than five years ago with a Konica Minolta triangulation laser scanner. Additional scans were capturedin Antikensammlung Berlin, Antikensammlungen München and recently in Museo Archeologico Bologna with an AICON SmartScan-HE C8 with 450 mm field of view and resolution of 0.1 mm .

 

Projection unit

Triangulation angle

Digital camera

 

Feature accuracy of the system is better than 0.030 mm. The field of view covered the whole vase at a resolution necessary for comparison at the mm to sub-mm level. The accuracy of the system ensured that data acquired at different locations can be compared to each other. Most head vases show very dark and shiny areas in combination with light paintings. This range of material properties (contrast, shininess, etc.) is not straight forward for scanning and required high- dynamic range scanning mode and careful scanner positioning as well as data processing to avoid artefacts in the resulting models. Working with color cameras in the scanner allowed capturing shape and color texture at the same time. In the software OptoCat 3D color textures may be switched on or off. For shape analysis color textures are not useful. For presentation and artistic interpretation color textures can be switched on.

Placing 3D models next to each other allows for a quick comparison of the 3D data. Please note that only 3D models were used for the geometric comparison and that no texture data was used. We are convinced that Beazley’s groups are principally correct. Nevertheless, recent computer technology and visualization systems can help to further refine and consolidate the original groups, in respect to chronology and production process. Conventional archaeological methods are inappropriate for these three-dimensional comparisons.

Shape comparison was performed in AICON´s OptoCat software (AICON, 2017). Two candidates were roughly aligned manually and the region of interest that was molded was selected by hand (Figure 4). A fine alignment of the selected areas was performed in OptoCat software which uses an implementation of the iterative closest point algorithm for alignment. After the alignment, the distance between two models was calculated for all vertices and was plotted.

Placing several head vases of different sizes next to each other, they appear like scaled models of each other. Applying a liner scale factor of 10 to 15% in x, y, z direction, the digital models were adjusted in size and compared to each other as before.

Results and Discussion

Differences of ±1mm were assumed to indicate a close correlation between head vases. For several vases deviations were small enough to assume that they originate from the same mold.

Comparison of scaled models also revealed small offsets. This variation maybe due to shrinking during oven-burning for vases originating from the same mold or may indicate that additional molds were taken from finished vases to produce a set of smaller vases.

Conclusions

Quantitative analysis of digital scans allows for comparison of 2,500 year old attic head vases. Several vases appear to originate from the same mold. In addition, scaled versions indicate that series or generations of vases exist.

Working with a digital data sets allows for testing many hypotheses in a fast way, even for large regions. Traditional methods would have to rely on a small number of tactile manual measurements. The current results add to the qualitative analysis performed almost 90 years ago by Beazley as well as observations by archaeologists that formulated similar hypotheses for a long time based on thorough observation. With the help of three-dimensional models, these hypothesis can be tested today.

Acknowledgements

We acknowledge support by Kunsthistorisches Museum Wien, Staatliche Antikensammlungen München, Antikensammlung Berlin. The project is also supported by the Fritz Thyssen Stiftung.

References

Beazley, J. D. “Charinos”, JHS 49, pp. 38-78, 1929.

AICON 3D Systems.” OptoCat User Manual”, 163p., 2017.