SCIENTIFIC INVESTIGATION ON PROVENANCE AND TECHNOLOGY OF A BLACK FIGURE AMPHORA ATTRIBUTED TO THE PRIAM GROUP
P. MIRTI, A. PERARDI and M. GULMINI
Dipartimento di Chimica Analitica, Università di Torino, via Giuria 5, I-10125 Torino, Italy
and M. C. PREACCO
Soprintendenza per i Beni Archeologici del Piemonte, piazza San Giovanni 2, I-10122 Torino, Italy
Restoration of a Greek black figure amphora gave an opportunity to study provenance and production technology of the vase. The composition of the ceramic body, determined by ICP-optical emission spectroscopy, matches that of Attic products. Investigation by X-ray diffraction and reflectance spectroscopy suggests a maximum firing temperature around 900°C and a body re-oxidation temperature around 800°C, respectively. Morphology and composition of black, red and dark red surface areas were studied by scanning electron microscopy and X-ray energy dispersive analysis; black areas show the features of a typical well vitrified black gloss, while the red areas were most probably obtained by simple burnishing of the body; dark red additions, on the other hand, are the likely result of a partial re-oxidation of a clay-ochre mixture.
KEYWORDS: PRIAM GROUP, BLACK FIGURE AMPHORA, PROVENANCE, TECHNOLOGY, ICP EMISSION SPECTROSCOPY, SCANNING ELECTRON MICROSCOPY, ENERGY DISPERSIVE X-RAY ANALYSIS, X-RAY DIFFRACTION,
INTRODUCTION
The municipal historical and archaeological museum in the town of Bra (Piedmont, Italy), housed in the medieval Palazzo Traversa, contains, besides a large number of archaeological finds from the nearby Roman municipium of Pollentia, a collection of ceramic wares from various Italian archaeological sites and of different date. Among these, a fragmentary amphora of likely Attic origin stands out, due to its large size and the elegance of the black figure decoration. The amphora, several fragments of which are preserved, has been recently subjected to complete restoration in the Restoration Laboratory of the Museum of Antiquities in Torino; the available fragments were reassembled and the missing parts integrated, in order to reconstruct the vase shape and the decorated scenes.
The vessel may be recognized as a type A amphora, a shape found in Attic figured production since about 530 BC (Sparkes and Talcott 1970). It features on either side an elaborated figured scene, placed within a rectangular metope accurately framed by parallel black and dark red lines, while a rich accessory vegetable decoration (palmettes) runs on the neck and the handles.
The main scene is the most difficult to read; it depicts the capture of the three-headed infernal hound Kerberos at the entrance of Hades, one of Heracles’ labours. The scene was probably attended by a number of gods, among which Athena survives; the quadriga stood behind her. Some left black letters from the hero’s name allow its identification, but only the club and the leonté, the lion skin, survive.
The other scene is the best preserved one and features a bearded Dyonisos seated in the centre holding a kantharos among Sileni and Maenads; gods and other mythological characters (Hermes, maybe Ariadne) are also present and attend the banquet.
The subject of the scenes, the iconographic and stylistic schemes, the accuracy of details and drawing, the execution of the accessory decoration, all suggest an attribution to the workshop
of the Priam Painter (Beazley 1956; Moon 1983; Iozzo 2002), an Attic vase painter active in the last decades of the sixth century BC (about 515-500 BC). Many vases by him, mostly large-sized, come from Etrurian tombs and belong to important collections. It is plausible that the amphora in Bra was part of a collection owned by the Savoia royal family; king Carlo Alberto, in particular, had a valuable vase collection housed in the nearby castle in Pollenzo. Black figure and red figure Attic vases were part of this collection, and were a present by Maria Cristina of Savoia, who promoted the beginning of archaeological excavations at Veio in 1838 (Mercando 2004).
Evidence of previous restorations was present on part of the fragments, and some of these could actually not belong to the vase under consideration; in particular, fragments coming from two different feet could be recognized. During the recent restoration work, samples were taken to be subjected to a series of analyses by different analytical techniques in order to obtain information on production technology and provenance, and to distinguish between pertinent and non-pertinent fragments from the two different feet.
EXPERIMENTAL PROCEDURE
Samples were taken from the ceramic body and from the decorated surface. Four samples (PR1-PR4) were taken from the ceramic body of shards which could be confidently reassembled as parts of the original vase. One of these samples came from a fragment which was part of the neck of the amphora near the handle junction (PR1), a second one from a fragment which could be placed above the metope featuring Dyonisos (PR2), and the third one from below the metope depicting Heracles and Athena (PR3); the last of these samples (PR4) was taken from a foot remnant, still attached to a fragment of the main body. Other two samples (PR5 and PR6) were taken from fragments coming from the two different feet. All the body samples (several hundred milligrams each) were obtained by detaching chips from
the thickness of the fragments, using a diamond coated saw; a diamond coated tool was subsequently used to remove any surface layer before grinding in an agate mortar.
An aliquot (100 mg) from each powdered chip was refired at 1000°C for 2 hours in quartz crucibles, and then fused with a twofold amount of lithium metaborate at 1100°C in graphite crucibles; the melt was dissolved in 1% HNO3 (50 ml) and properly diluted for elemental
analysis. The solutions thus obtained were analysed by ICP-OES using a Varian Liberty Series II sequential instrument equipped with a quartz torch (1.8 mm inner diameter) and a K-type concentric nebulizer mounted on a standard spray cyclonic chamber. The following 19 elements were determined: Al, Fe, Ca, Mg, K, Na, Ti, P, Mn, Ba, Sr, Cr, Ni, V, Rb, La, Y, Sc, Cu. Analytical settings were the same as reported in Mirti et al. (2004 a); for copper, not analysed in the cited work, the analytical line was 327.396 nm.
A second aliquot of powder from each sample was used for colour measurements by means of a Minolta CM-805i reflectance spectrophotomer, equipped with a pulsed xenon arc lamp and a barium sulphate coated integrating sphere; samples were viewed at an angle of 8° to the normal (d/8 geometry) and the reflected light (specular component included) was detected by a silicon photodiode array allowing one to obtain a spectrum in the range 400-700 nm with wavelength pitches of 20 nm. Colour coordinates were expressed in the CIEL*a*b* colour system, with reference to the D65 illuminant (average solar light) and the 10° viewing
angle. Data obtained for each sample were the results of an automatic average performed by the instrument on three successive measurements. Colour measurement was performed on unrefired samples and repeated after refiring at increasing temperatures (600, 700, 800, 900, 1000, 1050 and 1100°C). Each refiring was carried out under oxidizing conditions, maintaining the selected temperature in the kiln for four hours.
A further amount of samples PR1, PR3 and PR4 was examined by X-ray diffraction using a D5000 Siemens diffractometer, equipped with a copper anode (λ=1.54178 Å), and operating within a 2θ range from 5° to 50°.
In order to investigate the technology of production of the painted decoration, small chips were taken from four other shards for SEM-EDS examination. One sample (PR7) came from the decoration featuring parallel black and dark red lines on red background, at the upper edge of the metope depicting Dyonisos; another one (PR8) was taken from the black palmette decoration on red background, which bordered the other metope; the third sample (PR9) came from the red background of this same metope; the last sample (PR10) was taken from the black gloss at the left of the Dyonisos metope, and was divided into two parts (PR10a and PR10b).
Samples PR7, PR8, PR9 and PR10a were graphite coated for morphological investigation on fresh fractures by secondary electrons (SE) and backscattered electrons (BSE) by means of a Cambridge Stereoscan 360 scanning electron microscope. After morphological investigation, samples PR7, PR8 and PR9, as well as sample PR10b, were embedded in epoxy resin and polished using diamond paste down to 1 μm. The polished sections were graphite coated again and subjected to EDS analysis in the same Cambridge Stereoscan 360 equipment, coupled with an Oxford Instruments Link Pentafet 7060 detector, operating with 0.8 nA probe current, 15 kV electron acceleration voltage, 25 mm working distance, and 45 s total analysis time. EDS analyses of the ceramic body were carried out on 450 x 600 μm2
areas (200x magnification) on samples PR7 (two analysed areas), PR8 (three analyses) and PR10b (five analyses); an average body composition was calculated from all the obtained data. The composition of the black coating was obtained as the average of eight point analyses (diameter of the analysed area 5 μm) performed on samples PR7 (two point analyses), PR8 (three analyses) and PR10b (four analyses). The composition of the dark red layer was
obtained as the average of three point analyses performed on sample PR7. Element concentration maps were finally obtained on 60 x 80 μm2 areas (1500x magnification) of
samples PR7 and PR9, as a result of 35 iterations for every acquisition.
RESULTS AND DISCUSSION Chemical composition
Loss on ignition (LOI) after refiring for 2 hours at 1000°C was around 1.5% for all samples but PR6, which showed a much higher weight loss (5.7%). This would already suggest that the foot from which this sample was taken may not have belonged to the vase under study.
Table 1 reports the results of the ICP-OES analyses. It can be seen that data obtained for sample PR1 to PR4 are in good agreement, as expected for fragments belonging to the same vase; they were used to calculate mean concentration values (x) and standard deviations (s), also reported in Table 1, in order to attempt a recognition of the pertinent foot. One can observe that the concentration of all the analysed elements in PR5, but titanium, fall within the x±3s interval; on the contrary, the concentration of some of the major elements determined in PR6 (Al2O3, Fe2O3 and CaO), as well as those of strontium and scandium, are
found outside this interval. This result, along with the different LOI, would suggest that the pertinent foot is that from which sample PR5 was detached and that PR6 was taken from a shard which should not be associated with the vase.
A mean composition for the vase was then re-calculated by considering data obtained from all the pertinent fragments (i.e. PR1 to PR5) and is reported in Table 2. Iron content is indicated here as Fe2O3%, which mirrors the prevalence of iron (III) compounds in the red
body; FeO% is also reported in a note, to allow direct comparison with SEM-EDS data discussed later.
The mean vase composition was compared with published data on shards of Attic black gloss and red-figure pottery, selecting papers which report large sets of elements (Prag et al. 1974; Hatcher et al. 1980; Mirti et al. 2004a). The good agreement found, particularly regarding the high magnesium, chromium and nickel content that characterises Attic products, supports also from a compositional point of view the Attic attribution made on a stylistic ground.
Firing conditions
It is generally admitted that ancient Greek monochrome and bichrome coatings were produced through a single firing cycle consisting of a sequence of oxidizing and reducing steps obtained by varying the kiln atmosphere (Hofmann 1962; Tite et al. 1982; Jones 1986; Noble 1988; Maniatis et al. 1993; Mirti 2000).
In the present case, a maximum firing temperature has been evaluated by detecting the mineral phases present in the ceramic paste by X-ray diffraction (Kupfer and Maggetti 1978; Maggetti 1982), while an equivalent temperature of body re-oxidation was estimated by colour measurement (Mirti and Davit 2004). Quartz, haematite, plagioclases, potassium feldspars and diopside were detected in all of the three samples analysed by XRD (PR1, PR3, PR4). Absence of calcite and illite at a detectable level, and presence of diopside and potassium feldspars suggest a maximum temperature of firing around 900-950°C. This is consistent with firing temperatures usually evaluated for black gloss or figure vases produced in Greek or Hellenistic times (Maggetti et al. 1981; Tite et al. 1982; Jones 1986; Mirti and Davit 2001; Mirti et al. 2004 b).
An equivalent temperature for body re-oxidation was evaluated by measuring the colour of powdered samples of the ceramic body after refiring under oxidizing conditions at progressively higher temperatures: in this case, a change of colour should only be expected
after the original temperature of re-oxidation has been exceeded during refiring (Mirti and Davit 2004; Mirti et al. 2004 b). All of the six body samples were subjected to refiring and colour measurement; Figure 1 reports the colour developed by each sample with the increase of the refiring temperature as a point projected on the a*b* plane of the CIEL*a*b* colour space. All of the six samples show a progressive colour change which matches the trend reported elsewhere for Attic products, especially in the highest range of temperature (Mirti et al. 2004 b). Furthermore, the three samples from the main body of the vase (PR1, PR2 and PR3) share a very similar behaviour, while a wider colour variation is observed for samples PR4 and PR5, and a definitely more limited variation characterizes sample PR6. These results confirm that PR5 was part of the original foot of the vase, while PR6 comes from a non-pertinent foot. Finally, it can be seen that a significant change in colour occurs for samples PR1, PR2, PR3 and PR5 after refiring at 800 °C, while a less definite information is provided by sample PR4, due to a more progressive change in the low range of temperature.
Refiring of four out of the five samples belonging to the original vase thus suggests that body re-oxidation should have completed below 800°C. This temperature, however, may be lower than that of actual oxygen readmission in the furnace; in fact, if vents were opened during cooling, the temperature itself could have dropped somewhat before oxidizing conditions were restored in the kiln.
Painted decoration
Apart from the painted figures, black is found in the monochrome coating which covers all the vase but for friezes and metopes; as for red, it represents the background of the figured scenes, while dark red is found on details such as leaves and beards. Besides, black, red and dark red are found on the edges of the figured metopes, around the neck of the amphora and along the handles.
SEM images (Figure 2) show that the black slip is highly vitrified and uniform, some 20-25 μm thick and there is a sharp contact between the slip itself and the body. BSE images indicate the higher content of heavy elements in the slip than in the body, which is usually found in iron-rich Greek black gloss slips. In contrast, on images taken on sections of red areas, it was not possible to observe a proper slip separated from the body (Figure 3); at the surface, however, clay particles show a higher degree of vitrification and are more or less aligned in a direction parallel to the surface itself. According to BSE images, this layer should not have a different composition from the body. This is consistent with the practice of burnishing the surface of the vase before firing, in order to obtain a smoother and more shining red background. Most probably, the whole surface of the vase was burnished after shaping, and then the selected fine clay added upon it on the parts which had to turn black.
Figure 4 shows images of the surface and the section of an area decorated with alternating red, dark red and black stripes. The dark red stripe appears as a layer laid upon both red and black areas, with the red surface being the most porous on the left side and the black one the most vitrified, on the right. At a higher magnification, the BSE image of a cross section of this area clearly shows the porous red body and the vitrified black slip; upon both of them is found a thin layer, a few micrometers thick, whose composition is different from that of both body and slip, due to a higher content of heavy elements. One can then suggest that an iron rich layer was laid down on areas which had to feature a dark red hue, probably obtained by mixing a fine grained clay with an iron rich component such as ochre.
To go deeper into this topic, composition maps were obtained for major and minor elements. Iron maps, shown in Figure 5, confirm that this element is found at high levels in the dark red layer, with a concentration higher than that present in the black gloss itself; in contrast, different iron concentrations are not apparent throughout the section of a red area.
EDS data are reported in Table 3. First of all, these data allow a comparison between ICP-OES and EDS analyses of major and minor elements present in the ceramic body, pointing to a generally good agreement between them. Besides, data in Table 3 confirm the different composition of the black and dark red layers, and between each of them and the ceramic body. The black gloss features higher contents of aluminium, iron and potassium with respect to the body, and lower contents of silicon, calcium and magnesium. This agrees with data previously obtained for the black slip of Greek and Hellenistic monochrome and figure vases (Maggetti et al. 1981; Tite et al. 1982; Maniatis et al. 1993; Mirti et al. 1996; Mirti 2000; Mirti and Davit 2001; Mirti et al. 2004 b), and may be related with the potters' procedures of selecting and refining suitable clays for the vitrified coating.
As for the dark red layer, its composition is definitely different from that of the black slip; in fact, it is characterized by a very high iron content (more than 50%, expressed as FeO) and a low silicon content (25% SiO2); furthermore, aluminium is present at a level comparable to
that in the body, while the content of calcium and magnesium may be more or less related to that of the black gloss; finally, potassium is found in the dark red layer at an even lower level than in the body.
The peculiar features of the dark red layer, the black gloss and the ceramic body can be compared taking into account the silica to alumina concentration ratio, and the total contents of sodium and potassium oxides, and of calcium and magnesium oxides, respectively. In spite of the differences observed for the silicon and aluminium contents, the SiO2/Al2O3 ratio is
similar in the black and dark red layers, where it is about half that in the body; this suggests that, if a clay was used for the dark red layer, this was carefully selected and subjected to high refinement, like that used for the black slip. This is confirmed by the comparable total content of alkaline earths, which is some four times lower than in the red body. On the other hand, total alkalis in the dark red are half the content in the red body, and about 2.5 times lower than
in the black slip. This suggests that, if a flux (e.g. plant ash) was ever added to the clay used for the black slip to promote vitrification during the reducing step of firing, its use was deliberately avoided in the dark red layer to allow partial re-oxidation during cooling. The high iron content of the dark red layer strongly suggests that ochre may have been mixed with the low calcareous, highly refined clay, more or less similar to the clay selected for the black slip, to be suspended in water without flux addition; the suspension would have been laid down on either the burnished background (which had to turn red at the end of firing) or a previously laid clay slip (which had to become black and vitrified after firing). A low content in alkalis and a relatively limited amount of suspended material would have prevented the clay-ochre layer from complete vitrification during the reducing firing step, so that iron (II) compounds could be partially re-oxidized during cooling, leading to the development of a dark red hue. The fact that iron (II) compounds in the dark red layer were not completely re-oxidized though this layer was poorer in alkalis than the red background, may be explained with the high content of iron itself; in fact, iron(II) compounds may act as flux under reducing conditions and this could contribute in determining different degrees of vitrification for the black slip (complete vitrification), the dark red layer (partial vitrification) and the red background (no vitrification). Re-admitting oxygen in the kiln would have led to complete re-oxidation for red areas alone.
Conclusions
The scientific examination of a black figure vase attributed to the circle of the Priam painter has given support to an Attic provenance of it, as indicated by ICP-OES analysis of samples taken from body fragments. Chemical composition also indicated which, out of the two available feet, could be confidently reattached to the body during reassembling operations.
Examination of body samples by X-ray powder diffraction and reflectance spectroscopy has further suggested that the vase was fired up to a maximum temperature around 900-950 °C, and that body re-oxidation occurred around 800 °C. Colour coordinates of refired samples gave further support to the assignment of the vase to an Attic workshop and to the choice between the two available feet.
SEM images point to the presence of a 20-25 μm thick, well vitrified slip in black areas, while morphological features of red areas are consistent with the hypothesis that these were just burnished before firing. Furthermore, dark red areas are characterized by a very thin layer, a few micrometers thick, laid down either upon the black coating or the red surface of the vase. EDS analyses further pointed to high contents of aluminium, iron and alkalis in the black gloss with respect to the underlying body, while no difference in composition has been observed in cross sections from red areas. The dark red layer was found to contain more than three times iron oxide than the black coating, while the alumina to silica ratio and the total alkaline earth content are similar in the two layers; total alkalis are found in the dark red layer at a level lower than that observed in both black gloss and body. All this suggests that the dark red layer may have been obtained from a mixture of a highly refined clay and ochre.
Acknowledgments
Financial support of the Italian Ministry for University and Scientific Research is acknowledged. Authors are also grateful to Carmela Sirello, Marina Giaretti and the restorers of the Restauration Laboratory of the Museum of Antiquities of Torino for their kind cooperation. The restoration of the amphora, which gave the opportunity for this scientific investigation, was financed by the Regione Piemonte (Ufficio Beni Culturali) and the Municipality of Bra.
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Figure captions
Figure 1 Projection on the a*b* plane of the CIEL*a*b* colour space of the points representing the colour of powdered body samples refired at 700, 800, 900, 1000, 1050 and 1100 °C under oxidizing conditions. Blank symbols represent the unrefired samples and lines join points obtained for increasing refiring temperatures. Symbols: () PR1; () PR2; () PR3; () PR4; () PR5, () PR6.
Figure 2 Back scattered electron image of a fresh fracture of sample PR10a (1000x).
Figure 3 Back scattered electron image of a fresh fracture of the red background on sample PR9 (1000x).
Figure 4 Back scattered electron image of the surface (50x; above), and secondary electron (1000x; middle) and back scattered electron images (1000x; below) of a fresh fracture of sample PR7, showing the dark red layer superimposed upon red background on the left, and black slip on the right.
Figure 5 Iron concentration maps obtained on polished sections of samples PR7 (dark red decoration on black slip, above, and on red background, middle; 1500x) and PR9 (red background, below; 1500x).
