Multi-Method Analysis of Painting Materials in Murals of the North Mosque (Linqing, China)
Round 1
Reviewer 1 Report
The manuscript shows a case study of the North Mosque murals through an multi analytical approach. Despite methodologically there are no innovative aspects, the manuscript is very well written and can be valid as a case of study. For this reason I suggest a minor revision to improve the manuscript contents before publication.
Introduction. A brief state of the art related to the analytical approaches used in other case studies of different regions and continents would be useful in order to validate the proposed methodological approach. In addition, the description in the introduction of the north mosque is too detailed considering the target audience of the journal. I suggest reducing it and focusing more on analytical techniques. Part of the information about the Moschea can be add in the materials and methods.
Figures 3d, 4b, 6b, 8b Is the atomic percent quantitative or semi-quantitative? Add this information in the caption.
Figure 7. Are there other elements besides arsenic and copper (i.e. contaminants)? add element maps if so.
Conclusions: considering the target of the journal, the methodological aspects must be more focused. Advantages of each technique considered? Were all the techniques necessary? Complementarity of techniques? Being a good case study highlighting the benefits of a multi-analytical approach can be useful for future readers.
Author Response
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Author Response.docx
Reviewer 2 Report
Your work is very well written, covering an interesting field of ancient painting on buildings with religious role. You you have conscientiously approached all the colours found and analysed them with the seriousness required for such a preliminary study. According to your study, which completes and confirms other studies on that epoque and will enhance the restorers knowledge, addressing the lack of available historical restoration information, ancient painters and decorators used ultramarine, emerald green, cinnabar, kaolinite, gypsum and carbon black pigments to enhance the sacred building and to attract the parishioners and pilgrims alike.
Author Response
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Author Response File: Author Response.docx
Reviewer 3 Report
The paper describes a detailed chemical analysis of fragments of culturally important wall paintings, with the aim to understand both the materials used in the original paintings and materials used in restorations. This work is clearly important for the future preservation of the works and also demonstrates the importance of multiple analysis techniques to fully characterise heritage materials.
Overall the work is very well presented, with a clear and interesting background of the paintings to put the results in context.
A meaningful set of samples has been selected for analysis and the quality of data obtained and subsequent analysis is generally good.
Most of the conclusions are well supported by the data but there are a few points which require some clarification.
Overall the paper will be suitable for publication in Coatings after some revision.
Specific points for revision:
1. From visible microscopy of several of the samples, the authors state that the sample has a refractive index either more than 1.662 or less than 1.662. Could the authors clarify in the paper how this result is obtained. I can see that this relates to the stated refractive index of the Meltmount fixative resin used in the analysis, but further details are needed.
2. From polarised light microscopy, the authors refer to a "non-extinction" phenomenon in the image - could the authors say more about this? Is this effect birefringence? Does this help with identification?
3. It is not clear from Figure 3c if all the particles in that image exhibit the same non-extinction effect or not. It would we useful if the same areas could be shown in single polarised and orthogonal polarised light and at the same scale.
4. Line 251, it is stated "The presence of oxalate minerals in the samples provides evidence for the existence of lower organisms like fungi, which either naturally exist in artifacts or could be generated via microbial metabolism and degradation processes. This substantiates that the murals were painted at a certain period of time." Can the authors therefore say anything about the time period when these murals were painted based on the presence of these minerals? If not this statement seems redundant.
5. Band assignments in the FTIR analysis of the blue samples are not convincing.
In detail: The broad band at 1037cm-1 (ascribed to the Si-O vibration) is very hard to ascribe to a particular mineral here since it is characteristic of many silicates. There are similar broad features in all the analysed samples, overlapping with sharper bands in the case of the white sample. The other band which has been tentatively assigned to ultramarine at 794 cm-1 is at best only a weak shoulder in the spectrum (not labelled) and could easily be, for example, the same band as labelled 796 cm-1 and ascribed to Si-O-Si in kaolinite in the white sample. Again this is hard to assign to a specific mineral. Overall the FTIR evidence for ultramarine is weak. However, the Raman data does provide strong evidence for ultramarine, so this in the end is a good example of the importance of using multiple techniques, and the authors could highlight that point.
6. Line 283 - change the wording, as Raman bands are due to scattering and not absorption.
7. In the analysis of the binder sample. Whilst the Py-GC/MS, FTIR and EDS data provide evidence that protein is present in the binder, the conclusion that this "might be animal glue" is weak and not well supported by the presented data and analysis. The authors state that (following reference 51) the 7.55% methyl pyrole detection from the Py-GC/MS "tentatively proves" the presence of protein-like material. It appears that other common protein containing binders stated in the paper (egg white, peach gum) could still be the one used here. The assignment to animal glue seems to be mainly based on it being the "most extensively utilised" binder, which is not based on the scientific evidence of this research.
The authors should provide more robust argument (perhaps referring in more detail to reference 51) based on the data collected here, or change the conclusion to acknowledge that other protein containing binders are possible. I am not able to access reference 51, so if there is specific information in the reference which clearly indicates the Py-GC/MS results here show an animal glue, it should be included.
Author Response
Please see the attachment.
Author Response File: Author Response.docx
Round 2
Reviewer 3 Report
The authors have made significant improvements to the paper to address the concerns of the reviewers. In particular they have clearly indicated where specific techniques gave strong evidence for identification of samples as well as cases where some techniques could not provide definitive identification.
The new version has more information about the techniques used and a more concise background about the murals, which is appropriate for publication in Coatings.
