Review Reports

Round 1

Reviewer 1 Report

The paper titled Investigating colours and techniques on the wall paintings of the ‘Tomb of the Philosophers’, an early Hellenistic Macedonian monumental cist tomb in Pella (Macedonia, Greece) reports the results of a detailed multi-analytical study of pigments and application techniques used in the making of the decoration of this Hellenistic tomb. The adopted methodology combines archaeometric characterization techniques (OM, portable-XRF; SEM-EDS) with multi-spectral imaging in order to understand the palette of colors used by the artisans that made the tomb and the application techniques, by accurately observing and describing step-by-step the different portions and decorative motives the paintings are constituted of.

In my opinion, the paper appears very thorough and detailed already at this draft stage, and the analytical study extremely exhaustive. Many useful details are provided regarding the production process (lines 508-517) and regarding the chromatic properties of pigments, as well as the mixing techniques (i.e. lines 366-370) and the combination of preparation layers in pluri-stratified portions of the decorations (i.e., lines 440-441; 462-464). Albeit without reaching the quality of the tombs of Vergina, the use of expensive and rare colors to emphasize the social status of the deceased is consistent within the tradition of Macedonian tombs.

 

The analytical part is clear but the instrumental apparatus succinctly described. Therefore there are just a couple of points that could be further substantiated:

-          Which is the spot size of the XRF portable instrument you adopted for the in situ measurements? This important information should be added in order to state which is the diameter of the analyzed area as to exclude the possibility that ranges are large enough to encompass multiple pigmented zones. In such a case, it should be defined that the XRF results do not refer to a single pigmented portion but may also include "intrusive" elements from neighboring colored zones. Please clarify this point further.

-          Regarding Pb observed in yellow pigments: did you consider the utilization of litharge, possibly in substitution of together with lead-based white? Although not adopted, XRPD analysis could be very useful to clarify the pigment typology by describing its crystallography and not only its quasi-qualitative chemical profile. This techniques could be adopted to strengthen your interpretations and to probe some possibilities inferred from chemical investigations.

-          Regarding SEM-EDS analysis: at some points, EDS investigation returned Si, Ca and Al that you interpreted as Carbon black, presumably as an indirect evidence because C was not acquired due to the carbon coating of the sections (line 216). Please state that this interpretation is based on the “absence” of chemical clues and inferred from the observation of the black colored pigments in the cross-sections and by the strong absorbance in IR-reflected images. However, BSE or SE high-resolution acquisitions, if acquired, could help to recognize the residues of charcoal elements in the pigment matrix and you could add them in the supplementary materials to support your interpretations.

-          In general terms, some SEM images, with indication of the areas/points where EDS analysis were taken, could be added in the supplementary materials, at least for the more complex microstratigraphic portions investigated by EDS.

-          regarding gypsum (table 2): it would be important to clearify if its use is intentional, i.e. as binder of the plaster?, or it’s a post-depositional phase related to sulphation. I suggest the second hypothesis, as it is commonly observed in mortars and plasters in humid settings exposed to air pollution, but you could demonstrate this aspect by analyzing the chemistry of the preparation plasters. Is it lime-based or gypsum-based? Please clarify this point. Probably it is calcium-based, as reported at lines 236-237, but some petro-mineralogical or chemical data regarding the characteristics of the preparatory plasters could be added in the text, as they have been sampled.

-          Page 12: the identification of two workshops on the basis of the use of two different greens seems too audacious, also because it basically constitutes the only possible indication of this argument. I suggest nuancing this aspect.

Finally: I just report some formatting mistakes:

-          line 85:  t. he

-          line 87: double closing squared bracket

-          lines 92-93: double closing squared bracket

-          line 365: “the and the”

In conclusion, the greatest value of this article is the minute analysis of the execution technique, at any step and level of analysis. It denotes a high-quality level of research for which I suggest minor revisions.

The english is good but I suggest a revision by a proficient english proof-reader.

Author Response

-          Which is the spot size of the XRF portable instrument you adopted for the in situ measurements? This important information should be added in order to state which is the diameter of the analyzed area as to exclude the possibility that ranges are large enough to encompass multiple pigmented zones. In such a case, it should be defined that the XRF results do not refer to a single pigmented portion but may also include "intrusive" elements from neighboring colored zones. Please clarify this point further.

 

Reply: We have added the spot size (nominally c. 1.3mm diameter) and clarified that the non-punctiform nature of the analysis may include surrounding materials (see Pella XRF New Figures).

 

-          Regarding Pb observed in yellow pigments: did you consider the utilization of litharge, possibly in substitution of together with lead-based white? Although not adopted, XRPD analysis could be very useful to clarify the pigment typology by describing its crystallography and not only its quasi-qualitative chemical profile. This techniques could be adopted to strengthen your interpretations and to probe some possibilities inferred from chemical investigations.

 

Reply: We are hoping to return to the site and undertake more measurements with macro XRF and hyperspectral imaging. At present, we don’t have access to XRPD instrumentation, unfortunately. We do agree that it would be a very useful addition to the analysis.

The presence of litharge is a possibility and we added a reference to it.

 

-          Regarding SEM-EDS analysis: at some points, EDS investigation returned Si, Ca and Al that you interpreted as Carbon black, presumably as an indirect evidence because C was not acquired due to the carbon coating of the sections (line 209). Please state that this interpretation is based on the “absence” of chemical clues and inferred from the observation of the black colored pigments in the cross-sections and by the strong absorbance in IR-reflected images. However, BSE or SE high-resolution acquisitions, if acquired, could help to recognize the residues of charcoal elements in the pigment matrix and you could add them in the supplementary materials to support your interpretations.

 

Reply: it is not possible at the moment to re-analyse the samples, so we have added a reference in Tab. 5 to IR-reflectance as a means to identify C-based blacks

Carbon black was interpreted as indirect evidence because: 1) no color bearing minerals or oxides were detected in the black layers, 2) the most representative and not contaminated black layer is on sample Pel-24 on top of a blue layer, which contains minute traces of Si and Mg and a lot of C together with Ca from the lime and Cu from the underlying blue layer and 3) the absorbance of IR. All this evidence excludes any other possibility for a black color and leaves no doubt that is a Carbon black layer.

Comment for the reviewer: The samples are not useable any more so reexamination them is not possible. Besides, in a polished section embedded in resin and coated with carbon it would be rather difficult to identify fine carbon or shoot particles with BSE or high magnification SE. 

 

-          In general terms, some SEM images, with indication of the areas/points where EDS analysis were taken, could be added in the supplementary materials, at least for the more complex microstratigraphic portions investigated by EDS.

 

-          regarding gypsum (table 2): it would be important to clearify if its use is intentional, i.e. as binder of the plaster?, or it’s a post-depositional phase related to sulphation. I suggest the second hypothesis, as it is commonly observed in mortars and plasters in humid settings exposed to air pollution, but you could demonstrate this aspect by analyzing the chemistry of the preparation plasters. Is it lime-based or gypsum-based? Please clarify this point. Probably it is calcium-based, as reported at lines 236-237, but some petro-mineralogical or chemical data regarding the characteristics of the preparatory plasters could be added in the text, as they have been sampled.

 

Reply: Based on the XRF analysis and SEM, the nature of the plaster is carbonatic. We do mention in Table 2 that the reason for the presence of S is unclear and that sulphation may have occurred. To further stress this point, we added that the latter is a likely explanation.

We added in the text: The plaster in cross-sections (sample Pel-4) and consists clearly of lime as a binding medium and crashed marble or calcite particles to give it extra sheen and transparency. Also, the coarse mortar (Pel-39) consists of lime as binding medium and clay. The XRF gives some S but this should be just a surface crystallization with S originating from the disintegration of organic material in the tomb.

 

-          Page 12: the identification of two workshops on the basis of the use of two different greens seems too audacious, also because it basically constitutes the only possible indication of this argument. I suggest nuancing this aspect.

done

 

Finally: I just report some formatting mistakes:

 

-          line 85:  t. he

 

done

 

-          line 87: double closing squared bracket

 

done

 

-          lines 92-93: double closing squared bracket

done

 

-          line 365: “the and the”

done

 

Reviewer 2 Report

 

The paper presents an extensive analysis of painting materials and techniques used for decoration of the early Hellenistic Macedonian tomb excavated in Greece at the beginning of the 21st century. The authors provide a broad introduction to the archaeological context and describe the technological and iconographical aspects of the decorations in great details. Experimental methodology chosen by the authors includes a wide range of imaging methods, involving visible light, ultraviolet and infrared and elemental composition analysis with the use of XRF and SEM-EDS.

The composition of the paper is clear and in most parts it is well-structured. It presents the successive stages of the research process in a systematic way, making it possible to understand and follow them easily. This is also due to a well-designed experiment in which subsequent analyses complement previous ones. The comprehensive discussion of the results, which corresponds strongly with the available literature on the subject should be appreciated. As well as the interesting insight on how the technological studies can fulfill the interpretation of the iconography. Although from the analytical point of view the presented research does not offer any novelty, it provides a significant contribution to the knowledge on the technology of ancient Greek painted decorations and therefore to heritage studies.

However, several aspects of the paper require a review and correction to provide a better understanding of the research and improve the clarity and the structure of the paper.

·        The paragraph describing the excavation and construction of the tomb (lines 44-65) should not be the part of the introduction. It should either be moved to a subsection in Materials and methods or a new section presenting the archaeological/conservation context can be created

·        The introduction lacks a discussion on the use of analytical methods in the study of wall paintings and at least a paragraph on this subject should be added

·        The abbreviations mentioned in line 70-71 (IRR, UVR, UIL, VIL) should be explained in consistence with lines 190-191

·        Scientific methodology should be described in more details. In particular the paragraph about the XRF, where the mode of measurements should be mentioned (if point analysis -what is the spot size), the choice of the areas for the study should be discussed, number of points per area, etc. Similarly details of the EDS analysis should be provided (analysis mode, voltage, etc.)

·        Abbreviation for the Scanning Electron Microscopy Coupled with Energy-Dispersive X-ray Microanalyser should be added in the headline and used consistently throughout the text (compare e.g. line 384, 389, 435)

·        Reference to Figure 18 in line 326 states that the SEM-EDS analyses are presented in this figure. In fact, Figure 18 presents microphotography, so this should be corrected and the type of the microscope should be specified.

·        Two optical microscopes are described in the Scientific Methodology section, but results of their use are not explicitly presented

·        In Table 1 Figures S13a-h from supplementary materials should probably be referred to instead of Figures3a-h (line 332-333).

·        Tables 2,3 and 4 lack reference to the XRF spectra from the supplementary materials, analogical to that given in the description for Table 1.

·        In the description of Figure 18 (line 351-352) designation of samples P.1-P.17 is mentioned, but it has not been introduced before. Further in the text, when the results for analyzed areas are discussed two designations are used (P.1… and Figure18a…), which is a complication and should be disambiguated.

·        A complete analysis and labels for all the visible lines on the XRF spectra presented in the supplementary materials should be provided. Particularly as the detected elements are mentioned in the Tables 1-4.

 

 

Author Response

• The paragraph describing the excavation and construction of the tomb (lines 44-65) should not be the part of the introduction. It should either be moved to a subsection in Materials and methods or a new section presenting the archaeological/conservation context can be created.

 

done

• The introduction lacks a discussion on the use of analytical methods in the study of wall paintings and at least a paragraph on this subject should be added

Reply: not clear what discussion on analytical methods would be required here.

• The abbreviations mentioned in line 70-71 (IRR, UVR, UIL, VIL) should be explained in consistence with lines 190-191

Reply: we have addressed the inconsistency.

• Scientific methodology should be described in more details. In particular the paragraph about the XRF, where the mode of measurements should be mentioned (if point analysis -what is the spot size), the choice of the areas for the study should be discussed, number of points per area, etc. Similarly details of the EDS analysis should be provided (analysis mode, voltage, etc.)

Reply: we have added the spot size to the description of the instrument. The areas analysed are reported in Fig. 14. Not clear what is intended by “number of points per area”.

The analysis with EDS in the SEM was done first on rectangular areas of several hundred microns in horizontal length and 5-30 microns width as the thickness of the pigment layer under examination permitted, in order to obtain an average (bulk) analysis of the whole pigment layer. This was followed by a detailed point analysis with a beam size of 3 μm at high magnifications on most of the individual grains contained in the paint layer in order to identify the particles and binding medium producing the overall color effect.

• Abbreviation for the Scanning Electron Microscopy Coupled with Energy-Dispersive X-ray Microanalyser should be added in the headline and used consistently throughout the text (compare e.g. line 384, 389, 435)

Reply: we addressed the inconsistencies

EDAX is a commercial firm producing microanalysis systems. We better use the abbreviation SEM-EDXA (Scanning electron microscope coupled with Energy Dispersive Xray Analysis). Please change to this throughout. I added a description of the microscope and analysis system in the techniques section.

• Reference to Figure 18 in line 326 states that the SEM-EDS analyses are presented in this figure. In fact, Figure 18 presents microphotography, so this should be corrected and the type of the microscope should be specified.

Reply: We have addressed the inconsistency

• Two optical microscopes are described in the Scientific Methodology section, but results of their use are not explicitly presented
• In Table 1 Figures S13a-h from supplementary materials should probably be referred to instead of Figures3a-h (line 332-333).

Reply: We have addressed the inconsistency

• Tables 2,3 and 4 lack reference to the XRF spectra from the supplementary materials, analogical to that given in the description for Table 1.

Reply: We have addressed the inconsistency

• In the description of Figure 18 (line 351-352) designation of samples P.1-P.17 is mentioned, but it has not been introduced before. Further in the text, when the results for analyzed areas are discussed two designations are used (P.1… and Figure18a…), which is a complication and should be disambiguated.

Reply: We have addressed the inconsistency

• A complete analysis and labels for all the visible lines on the XRF spectra presented in the supplementary materials should be provided. Particularly as the detected elements are mentioned in the Tables 1-4.

Reply: done

 

Reviewer 3 Report

The paper is well written and quite interesting and I don't think it needs important revision.

The main issue I found is about numbering and captions of the figure. In many cases the authors refer to multiple images but the caption is numbered only with the first cited figure. For instance, at row 264, "(Figures 6-7)" but the caption reports only "Figure 6" (Figure 7 is on the right of Figure 6 without any numbering and this is confusing). This happens for most of the multiple figures in the paper. So the authors have to choose if they want to put a number in the captions for each image or to add letters to the number and to the images (Figure 6a-b) to obtain a better connection with the text.

Furthermore, I found some typing errors in the text, so I suggest to check it carefully to emend these mistakes.

Author Response

The main issue I found is about numbering and captions of the figure. In many cases the authors refer to multiple images but the caption is numbered only with the first cited figure. For instance, at row 264, "(Figures 6-7)" but the caption reports only "Figure 6" (Figure 7 is on the right of Figure 6 without any numbering and this is confusing). This happens for most of the multiple figures in the paper. So the authors have to choose if they want to put a number in the captions for each image or to add letters to the number and to the images (Figure 6a-b) to obtain a better connection with the text.

Reply: We have addressed the inconsistency

Furthermore, I found some typing errors in the text, so I suggest to check it carefully to emend these mistakes.

Reply: We have addressed the inconsistency