The Characterization of a Fragment of a Medieval Fresco from Corbii de Piatră Cave Church

Round 1

Reviewer 1 Report

The manuscript reports an analytical study of a mural painting of the Corbii de Piatră Cave Church dated back on 13  century.  The study combine SEM-EDS, AFM,  MO and XRD to provide a well-conducted analytical characterization.  Unfortunately, the paper show extended parts that need major revision. In particular, the abstract, and the introduction.

General:

1) In the introduction the authors describe the fresco painting, introducing interesting historical artistic information.  However geological and/or mineralogical-petrographic information should also be introduced with reference to the artistic technique used by the Byzantines, these would serve to support the purposes of the study. Objectives however remain generally poor described both in the abstract and in the introduction.

For example, when the author write:” A first analysis with the naked eye of the existing frescoes revealed two situations for the support mortars: friable mortars that detach easily, even when touched, and very ad-herent, hard mortars”, They seem to want to begin talking about different types of mortar, or on the difficulties that the presence of two different types of plasters may entail at the analytical level for the heritage science. However, continuing in the reading, the authors do not deepen the discourse and the text lacks explanation on why it is necessary to study and characterize the materials of this Byzantine mural painting.

The authors are expected to clarify and strengthen the introduction, explaining the particular difficulties encountered.

2)As reported in the end of the introduction, the authors wrote: “The identification of the materials used in the construction of the fresco also allows us to understand the commercial exchanges on the territory of the country and the trade in pigments during the painting of the church, if the pigments used were of local origin or if they were rare  pigments that came from commercial exchanges. Knowing the nature of the pigments allows us to make associations with the fresco painting of other churches founded by Basarab I.”

While it promisingly stars, the patient reader is left with the disappointment that these interesting topic are not further discussed and barely appear in the text (without to cite references). The authors should rewrite the sentences, explaining that new knowledge on commercial exchange and trade in pigments might be achieved in future by their characterization/study. It seems that no new knowledge has yet been achieved in the paper. I suggest also an extensive revision of English languages and to resolve certain formulation issues.

From the reading of the discussion sections, it is evident that the discussion of the data is more oriented to the characterization of the materials used in this painting, both of the original materials and to study the effects of degradation that led to the formation of new phases in the painting. The authors should rewrite both the abstract and the introduction giving more space to the analytical part and resize the discourse on commercial routes or trade pigments, unless they have more consistent data to be reported or more robust references.

3) page2 line 90. Authors invited the readers to follow a reference [8] of a previous study performed on the same artwork. However, the reported reference is in Romanian language and for Not-Romanian readers could be hard to get information about this previous study. The authors should report a brief description of the previous study to improve the readability of the manuscript.

4) It is mentioned that a number of samples were taken and analyzed to study pigments see page 2 however, in line 92 the authors say that a single sample was analyzed. Is this sample divided into more pieces?

The Authors reported in page 3, the sample was embedded in resin and sanded by abrasive paper. I presume that this samples cannot be analyzed by AFM. The authors should clarify in the material and methods section, the experimental preparation of the samples to improve the readability of the manuscript.

If the single sample was divided, they also should indicate the amount and number of samples analyzed by the different techniques.

4) In the text many words are written with a hyphen in the middle, i.e page 2 line 52, 54,  70, etc. or sometime  The authors should revise and correct the typos to avoid the impression of negligence in their work.

5) Some paragraphs should be rewrite because appear without meaning and difficult to be readed.

For example: Page 4 “Under the red pictorial layer was identified a broad, ochre-brick colored layer, with a large thickness, in the case of Figure 4 of 192 µm with a diffuse limit to-wards the inside  of the fresco mortar, a fact that shows that this layer is the fresco mortar impregnated with red pigment by diffusion, in a wet state, which corresponds to the fresco technique, Above the layer with red pigment was identified the layer of green color deposition, which cor-responds to a crust of discontinuous bio-mineral degradation formed from calcite, gyp-  sum and dry lichen colonies”

Minor corrections:

Page 2 line 69-70 “When establishing the experimental program, the characterization strategies used at nation-al and international level were taken into consideration.” It is not clear the meaning of the sentence e a cosa sia riferito. à rewrite

Page 3 116-119 “The analyzes were performed in polarized light with the help of a Zeiss Ob- 116 server A1m optical microscope, which allows magnification up to 1000x, visualization in 117 bright field, dark field, polarized light and acquisition of images with a Canon camera. For characterization, the mortar sample was embedded in resin and sanded on abrasive paper to a roughness of 2000”. These sentences should move in Material and method section.

Page 3. In the caption of figure 1 the description of  a,b,c,and d is missed. In the text no comments are reported for figure 1b and 1d.

Page 4 144-149.  The references of figure in the text  are inconsistent sometimes there is for examples a point  sometimes a bracket. The authors should uniform the format.

Page7 224-227 These sentences should be moved in materials and method section.

Page 7 line 233 a Bracket is missing

Page 7 line 244-246 These sentences should be moved in materials and method section.

 

Author Response

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Reviewer 2 Report

The paper deals with an interesting subject and an exhaustive set of analytical methods was implemented. However, the paper in its actual shape is not ready for publication as the state of art, methods and results are not clear in terms of rationale, flow and descriptions.

Some remarks:

1-      Extensive English revision is required. Besides grammatical errors, several sentences are difficult to understand. For example:

-          Abstract, lines 25-27 “and its variation […]  were determined”.

-          Abstract, what does it mean “release process” (lines 26-27)?

-          Introduction, lines 54-55 “the votive painting of Mr. Basarab I”. It is unclear if the authors refer to the fact that Basarab I wanted it or if the fresco displays the figure of Basarab I.

-          Introduction, lines 69-72 “When establishing […] into consideration”. Please consider revising it.

-          Materials and experimental techniques, line 82 “following the preliminary study”. Which study is meant by the authors?

-          Materials and experimental techniques lines 81-91. The authors should consider avoiding repetitions.

-          Materials and experimental techniques, line 92 “a single sample […] performed. Was only one sample taken? Considering the images presented, more than one sample was collected and then analyzed. In this regard, a better explanation of the working flow of the analytical methods implemented would help.

2-      The state of the art is not exhaustive enough. In turn, the impact and relevance of the research are not clear. The authors may consider adding more information (along with relative references) about contemporary or similar mural painting studies. In addition, is it the first time this church has been studied?

3-      The aims and methods to address the goals are unclear (lines 67-79). For example, is the characterization of the fresco (paint layer + intonaco + mortar) the main aim? (in the abstract at line 24, only the mortar is mentioned). Or is the understanding of the factors causing the detachment? In addition, what is the usefulness of the results obtained? Can those be used to plan possible conservation strategies? Or can those be used to make comparisons with coeval mural paintings?

4-      The Materials and experimental techniques are missing information about the optical microscope and SEM-EDX. Lines 197-198 “The phase analysis […] Data).”, 224-225 “The experiments […] non-contact mode”, 244-246 “the SEM-EDS […] chemical analysis” could be moved to the materials section.

5-      The motifs of the mural paintings are not described, and the “red color” in line 89 lacks context. The author can consider adding an image or describing where exactly the sample(s) were taken and if they may contain a paint layer.  

6-      The results section is generally difficult to follow as the discussion of the results is not adequately supported by images/graphs. In addition, there is not a clear distinction between the presentation of the results and their discussion, and, in turn, their implication as the paper’s outputs. The author may consider improving the whole results section. References to the images/graphs should also be improved.  

7-      Figure 1. The author may consider presenting bright and dark field images also. It would support the understanding of the PL images. The caption lacks a, b, c, d image descriptions. Are they from the same sample?

8-      The authors refer to “luminescence” in the description of the PL images. Is it correct? Is it not the birefringent property of the materials?

9-      Is it correct the reference to Figure 3 at line 139? Figure 3 is not mentioned in the text, and its description seems lacking in the results section. The caption of Figure 3 refers to many details such as quartz, bioclast, etc. are those results obtained from the OMPL?

10-   “above” and “below” have been used to describe the OM images. To improve the readability, interpretation of the images (with contours and/or letters as in Figure 3) can be helpful.

11-   Lines 161-167 described the possible formation of saline efflorescence in the form of gypsum. Is that correct? Can we exclude other saline forms?

12-   Lines 203-209, did the authors identify the exact crystalline phases of calcium carbonate and calcium/magnesium carbonate?

13-   The results of the cathodoluminescence are not described (besides lines 206-209). Can the authors provide more information about the results? For example, was cathodoluminescence a relevant investigation tool? If not, why?

14-   AFM is a very sophisticated method. The aim of the AFM investigation is described from line 225 until 229. However, they do not find a match with the results section (the authors conclude simply that the mural painting was made using a brush). Can we extrapolate more information from the AFM study? Did the authors verify the presence of a single material or multi-component nature (see line 228)? In addition, why did the authors mention “ceramic surface”? Did they consider the fresco as a ceramic surface?

15-   The SEM-EDX detected sulfur on the upper side (see Figure 9, S kalpha1). Therefore, the sentence at lines 259-261 “Throght the thickness […] corrosion process.” can be misleading.

16-   If Figure 10 is intended to be qualitative, the authors may consider presenting the EDX spectra in log scale.

17-   The caption of Figure 10 describes for the first time all the layers of the fresco. Why do the authors not use the same terminology before (e.g. in the description of the OM images)?

18-   Any Si-containing mineral was detected by XRD. Is that correct?

19-   Pb is not mentioned in Table 1. How was Pb then identified?

20-   The sample(s) should be covered with a biological patina, following the description provided in the introduction. Can the authors describe their nature better and if their presence has influenced the effectiveness of the analysis performed? Did the authors have to remove it?

21-   The conclusions are the clearest part of the paper. However, it can be shortened, highlighting the most important outcomes.  

Author Response

Thank you for your comments!

Pleas to find our responses in attachments!

Best regards!

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

The authors have corrected the laper as request. I suggest to accept the paper for publication

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 2 Report

Most of the comments raised were implemented in the paper. The reviewer thanks the authors for having considered the comments. Even though the paper has undoubtedly improved, some points still exist to correct before publication. Please read them below:

-          Line 27, “[…] in the fresco layer from […]”. The term layer can be misleading. Consider removing it.

-          Thank you for adding Figure 1. However, there are several points to address: i) it is not cited in the text. ii) The authors should also graphically explain where image Fig.1c is located in the overview (Fig.1a). iii) Fig.1d does not have still context as the red paint layer is not cited yet. iv) The caption should read “b-layout of the mural paintings in 2011”. v) In addition, the authors can consider adding in the main article text the information/comment provided during the first peer-reviewing round about the crust deposits (“In the current stage, the fresco of the church is mostly covered by a crust of deposits”) and about the fact that the mural paintings were visible in 2011, while today are not (“12 years ago, parts of the fresco were still visible”)

-          “interdisciplinary” is repeated twice in lines 77 and 81. Please avoid repetition.

-          The beginning of the sentence in lines “77-78” is not clear in English. What does it mean “advanced interdisciplinary characterization”?

-          The sentence provided as a reply to the reviewers, “The experimental program for achieving the objectives was established considering the strategies used nationally and internationally in the characterization of old frescoes.” is much more straightforward than the sentence in lines 61-62. Therefore, consider merging or replacing it.

-          “mortar sample” is used often in the text. If it means the whole stratigraphy, including the painting layer, the author may consider using “fresco sample”.

-          Lines 98-101 are not clear. Consider adding information on the good adhesion and presence of a red pictorial layer.

-          “Figure 2a” at line 165 should be corrected as “Figure 4a”.

-          Please add in the caption of Figure 4 that those images are the results of the cathodoluminescence analysis. Please also explain the main difference between A and B images if they come from the sample samples. For example, are they two different fragments? If so, the authors can consider explaining that a single fresco sample was taken but then dived into several fragments and prepared depending on the analysis (e.g. resin optical microscope).

-          The paragraph at lines 170-176 is out of position as information about gypsum is not provided yet. The authors can consider changing its place in the text.

-          Line 182 should read, “Beneath the unaltered layer […]”

-          The section of the XRD results (lines 208-230) is also out of position as it presents the conclusive material characterization. The authors could move the paragraph after the SEM-EDS analysis.

-          Text in lines 226-227 seems more like a comment/interpretation than an analytical result. It should be without the bullet.

-          “ceramic material” is still cited in the text (line 242). Is it intentional?

-          Sentence in lines 249-250 is unclear and reports strange dimensions that are different from the caption of Figure 7.

-          Comments on lines 258-262 are also not explicit. What are the two different orientated materials? What does it mean that no alteration was observed? 25x25 um? The caption of Figure 7 reports 12x12 and 6x6 um. Please consider explaining better.

-          Caption Figure 8 should read “intonaco”.

-          Consider modifying the caption of Figure 11, as the bottom image is not properly explained.

 

-          The conclusions are still long and the last sentence should be better introduced. But it is more a personal taste. The reviewer is also missing a comparison with other coeval or comparable case studies. The references do not have to be in English. It is more important to state how much your findings are close and/or innovative with respect to previous studies on the same church or similar. 

Author Response

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Author Response File: Author Response.docx