Multi-Scale Characterization of Unusual Green and Blue Pigments from the Pharaonic Town of Amara West, Nubia

Round 1

Reviewer 1 Report

The paper titled "Unusual green and blue pigments from ancient Nubia" by K. Fulcher et al. deals with a multi-analytical characterization of different pigments found in the pharaonic town of Amara West, collected during a recent excavation of the site by the British Museum, from 2008 to 2016. Authors, starting from the detection of uncommon minerals in some samples with respect to those typically observed in any Nile Valley context, highlight the employment of rarely-used pigments providing useful insights about the pigmenting agent used in urban settings.

The excavated site is of great interest and the used methodology is appealing. The reported data are not particularly detailed resulting, in some part, too succinct and not properly convincing. On the contrary, I found the discussion section very good, containing plausible hypotheses and assumptions on the basis of the main results achieved.

Based on the aforementioned considerations the paper deserves, in my opinion, publication in the journal Heritage - as it contributes to the knowledge of the composition, both at the elemental and molecular scale, of pigments used in a context which is not that of elite and/or funerary, nowadays more frequently examined.

Some issues are listed below:

1. In my opinion, the title of the paper should be modified, as no mention to the “characterization” is present. A possible alternative could be “Multi-scale characterization of unusual green and blue pigments from the pharaonic town of Amara West, Egypt”.
2. Please, add the full affiliations, including addresses and countries for each author.
3. The specific type of pigmented material should be specified in the abstract since it is currently missing. Please also change “infrared spectroscopy” in “Fourier transform infrared spectroscopy in attenuated total reflectance geometry (FTIR-ATR)”
4. “The majority of the blue pigment samples were Egyptian blue, but some were found to be a blue earth, the main component of which was the sodic amphibole riebeckite, which appears to have been used as an alternative”. A re-phrase of this sentence is strongly recommended.
5. The introduction section needs to be expanded. Authors should include, in the broad framework of the archaeological examinations carried out through various spectroscopic techniques, some sentences about the importance of the identification of pigmenting agents employed by art-workers/painters/manufacturers/craftsmans in order to reconstruct the historical–geographical context of the finding, and how the use of specific pigments can represent the stylistic expression of an artist or an epoque. Such addition should be added before the description that is already present which specifically describes (correctly) the study of pigments but limited to the investigated region/context. Authors are encouraged to accompany the new part with some references. Some of the many references could be: doi:10.1016/j.culher.2019.07.026; doi:10.3390/geosciences9040172; doi:10.1186/s40494-020-00438-4; doi:10.1155/2018/8295291; doi:10.1016/S0022-2860(96)09422-7; doi:10.1140/epjp/i2018-12231-7; doi:10.21014/acta_imeko.v10i1.824.
6. “Together, these areas contained over 300 ceramic sherds with pigment on the concave surface”. Please change in “In addition, these areas contained over 300 ceramic sherds with pigment on the concave surface”.
7. “Additionally, attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR) was used to confirm identification in some cases (Castro et al. 2003).” Please change in “Additionally, Fourier transform infrared spectroscopy in attenuated total reflectance geometry (FTIR-ATR) was used to confirm identification in some cases (Castro et al. 2003).”
8. “FTIR analysis was inconclusive in analysing this phase”. It is not clear in the text why the FTIR does not support the presence of granite accessory minerals zircon and apatite. Please comment.
9. “A sample of the greyish blue pigment from palette PS539 analysed by XRD was found to contain chlorite (variety clinochlore), and the blue-coloured sodic amphibole riebeckite (Figure 6). The EDS analysis (Table 1) is broadly consistent with this composition, but the low values for Na, K and, perhaps, Ca are somewhat puzzling. This material is best characterised as a naturally occurring blue earth.”. This sentence appears quite misleading and confusing. Authors stated that XRD revealed the presence of clinochlore (Mg₅Al(AlSi₃O₁₀)(OH)₈), in which no Na, K or Ca element are in any way present. In the light of this, why authors state that “the low values for Na, K and, perhaps, Ca are somewhat puzzling” ?. On the basis of what assumption/evidence the greyish blue pigment can be considered made up of naturally occurring blue earth?
10. If it is possible provide figure 6 and figure 8 with higher quality.
11. Please add the full name of DTGS (deuterated triglycine sulphate).
12. In my opinion, the conclusion section should be re-written. It is hardly understandable and does not provide a clear explanation of the main points of this study as well as of the different experimental methods employed. I suggest to put in evidence the state-of-art in this field of research, what is sought and main achievements found.
13. English should be improved throughout the manuscript. I would suggest a careful revision of the English style by a native English speaker.
14. Several format issues can be found throughout the manuscript (i.e. reference format). Please carefully follow the MDPI template before re-submission.

Author Response

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Author Response File: Author Response.docx

Reviewer 2 Report

This paper is well written and it presents some new results about green and blue pigments in Amara West (ancient Nubia). These results are in general well discussed.  Some improvements can be carried out to clarify some points:

1. I find there is an important lack in the methodology concerning the samples. Was exactly the "same sample" from a fragment analyzed for all the techniques? For which techniques the same sample was used? What was the amount of sample used? Please, clarify this. Please, include a discussion about the heterogeneity of the samples and stress its implications.
2. Do you have any colorimetric measurements? It is important considering a possible intentional selection of the color and the use of raw materials. Please, include some measurements if possible.
3. If you carry out SEM-EDS, I find very difficult to measure the stoichiometry as written: “SEM-EDS analysis of polished sections of blue pigment gave the atomic ratio Ca:Cu:Si:O 1:1:4:10 indicating that the material was calcium copper silicate CaCuSi4O10”. Please, include in all the SEM-EDS measurements the corresponding uncertainties and the significant figures (table 1, 3, and supplementary table 1). 
4. Please, write properly the chemical formulas: CaCuSi4O10 and (Cu2Cl(OH)3

5. Please include some references to support the cuprorivaite finding. For instance: Jaksch, H., Seipel, W., Weiner, K.L. et al. Egyptian blue — Cuprorivaite a window to ancient Egyptian technology. Naturwissenschaften 70, 525–535 (1983). https://doi.org/10.1007/BF00376668

6. How do you explain the low amount of Na in the riebeckite EDS results? It was the same sample analyzed for XRD, FTIR and EDS? Please, discuss this point.
7. In table 1, please write Region 1 and Region 2 not only 1 and 2 in the head.
8. For “The bright green pigment from the grindstone”, please include the atacamite FTIR bands used for the identification in the corresponding paragraph. In this case, it was not used XRD?, why?
9. Correct in the XRD methodology – a polished silicon wafer -
10. What can you say about the bands 792 an 594 cm-1 in the FTIR spectrum of PS132 blue of Figure S2? Can you relate them to any material?

Author Response

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Author Response File: Author Response.docx

Reviewer 3 Report

In general, I’m very happy to participate as a reviewer in this particular work, as the subject is very exciting. The authors provide a very precise analysis of the materials under study, using appropriate characterization methods. The discussion part is also extremely interesting. To sum up -without being exhaustive-, I believe this work is interesting, well executed and well presented. I have nothing to add, except some minor aspects, mainly regarding the journal’s template:

1. Please, use the provided template. Eg, numeric appearance of citations
2. Check the manuscript for additional spaces between words, eg intro, line 2, after papyri, p. 5, last line between as and a, results, green pigments, between typically and anomalous
3. Please, insert space between amount and values, eg 2, Amara West, 2^nd line 108x108 m, 0.50 s in the caption of Fig.6.
4. Although the manuscript is very easy to follow, consider changing your results numbering as “3. Results, 3.1 Blue pigments, 3.2. Green pigments.
5. As the journal doesn’t have a page or figure limit, consider including your supplementary figure and table inside the manuscript, they are too interesting to be left apart.
6. Results, blue pigments, page 5, line 5. Please use subscript for the stoichiometric numbers of CaCuSi4O10 and the same for (Cu2Cl(OH)3
7. Please, use a more thick line for plotting the FTIR spectra, and bigger font sizes for all the lettering of the spectra (annotated wavenumbers, axes names and values, spectra titles). The same for the XRD patterns, as it’s almost impossible to read the phases and the quantitative analysis inside the plots (the greenish hue use for some phases is not helpful at all).
8. Discussion, 3 lines before the end of first paragraph. Better “Experimental work by the authors has shown”
9. The proposed template has the “materials and methods” section before the presentation of the results.
10. 6.2 upper case for -1 in wavenumbers
11. 6.3 coating for conductivity? Measurement conditions (accelerating voltage, probe current, working distance)?

Author Response

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Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

Authors have seriously taken into account all my suggestions/comments. The paper has been improved. In the present form the paper can be published.