Organic Patinas on Small Historical Bronzes: From Mock-Ups to Actual Artworks

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript is very interesting and well-organized. It shows the problem around historical bronzes' organic patina conservation and an interesting multi-analytical evaluation approach. Just a few comments and suggestions to improve the manuscript:

-please remove bold in the abstract

-in the Figure 1 caption, please better explain the Figure 1 a) set of mock-ups 

-in Figure 2, I'm missing the letters (a) to (g), as indicated in the figure caption. Please add

-in the Table 1 caption, please include not only the abbreviations for ED and OCT

-In the Figure 6 caption, please include not only the abbreviations of ROI and OCT

-In Figure 7, please completely write RO and CCD

Author Response

The manuscript is very interesting and well-organized. It shows the problem around historical bronzes' organic patina conservation and an interesting multi-analytical evaluation approach. Just a few comments and suggestions to improve the manuscript:

We are glad that the reviewer found the work interesting and welcome her/his suggestions.

-please remove bold in the abstract

DONE

-in the Figure 1 caption, please better explain the Figure 1 a) set of mock-ups 

We added a few words to explain that the samples are made with various organic coating on coupons of Cu-based alloy

-in Figure 2, I'm missing the letters (a) to (g), as indicated in the figure caption. Please add

DONE

-in the Table 1 caption, please include not only the abbreviations for ED and OCT

The meaning of EC and OCT acronyms are explained in the text, when the techniques are first mentioned (EC page 2 , OCT page 2  ), so we avoided to repeat that in the Table caption. We corrected ED in the Table 1 caption with EC, the acronym for Eddy Current that we use along the text.

-In the Figure 6 caption, please include not only the abbreviations of ROI and OCT

The meaning of ROI and OCT acronyms are explained in the text, when they are first mentioned (ROI page 12 , OCT page 2  ), so we think that avoiding repetition makes the text lighter.

-In Figure 7, please completely write RO and CCD

See above. We completely wrote CCD (Charge-Coupled Device) at page 13.

Reviewer 2 Report

Comments and Suggestions for Authors

The article is interesting and concerns the authors' own experience in the analysis of protective coatings on small metal (bronze) historic objects using non-destructive techniques. The concept of the work involves the analysis of model, hand-prepared samples with coatings made according to old recipes simulating historical coatings and, on this basis, the analysis of coatings on the original relief.

I have the following comments.

We receive information that this is a fragment of a larger project partly in the introduction and partly in the conclusions. It seems to me that this information should be included in the introduction and not in the conclusions. Then the reader knows that the presented results do not exhaust all issues but present a certain research concept. Another option could be to add one section titled "future work" (containing the content of the last paragraph in the current conclusions). I think that the conclusions should only include conclusions from the current work.

Another issue is to specify more precisely the purpose of the research presented in the current work. I think it is best to do it in points, and then refer to these points in the conclusions and show their execution. In other words, it is intended to separate the goals of the overall project from the goals of the current article.

I think it would be important for readers to discuss in more detail the capabilities and suitability of each of the methods used for the analysis of small-sized objects.

How do the authors expect to find correlations between the original coating and patterns made in the laboratory? Visually or using machine learning methods?

Page 3, what kind of abrasive paper (granulation) was used to prepare the surface, and was the surface degreased?

In Figure 2, the markings a, b, ...., and g are missing.

Table 1 should be narrowed by reducing the width of the second, third and fourth columns.

In the references, in [26], the title of the journal should be in abbreviated form. The title of the article is missing in {33]. In [35] should be Wiley. Many places are missing spaces.

Comments on the Quality of English Language

I have no comments, the text is understandable.

Author Response

The article is interesting and concerns the authors' own experience in the analysis of protective coatings on small metal (bronze) historic objects using non-destructive techniques. The concept of the work involves the analysis of model, hand-prepared samples with coatings made according to old recipes simulating historical coatings and, on this basis, the analysis of coatings on the original relief.

Thank you for reviewing our manuscript and for your suggestions. We have taken into consideration the observations made and organized the answers to the raised concerns here following.

I have the following comments.

We receive information that this is a fragment of a larger project partly in the introduction and partly in the conclusions. It seems to me that this information should be included in the introduction and not in the conclusions. Then the reader knows that the presented results do not exhaust all issues but present a certain research concept. Another option could be to add one section titled "future work" (containing the content of the last paragraph in the current conclusions). I think that the conclusions should only include conclusions from the current work.

The reviewer is right. For clarity, we have moved the information about the general project to the introduction, with explanation on the goal and description of the future work to produce more mock-ups and test more analytical techniques (from line 25 page 2).

Another issue is to specify more precisely the purpose of the research presented in the current work. I think it is best to do it in points, and then refer to these points in the conclusions and show their execution. In other words, it is intended to separate the goals of the overall project from the goals of the current article.

In the final part (from line 40 page 2) of the introduction, we have specified the aim of this preliminary work, i.e. to start building a collection of reference materials and related analytical data to be shared among researchers working on this subject and to set an investigation protocol mainly based on not invasive techniques. In the conclusions, we added a table (Table 3) where We hope that the purpose of this preliminary work and the achievements are now clear in the framework of the broader project.

I think it would be important for readers to discuss in more detail the capabilities and suitability of each of the methods used for the analysis of small-sized objects.

This is a key point of the work. In principle, there is no size upper limit for all the analyses proposed. Big objects require multiple acquisitions that have to be stitched in a single image.

For small-size objects the only limit is set by the instrument lateral resolution: depending on the technique, the spot size defines the minimum acquisition area. Each instrument is well described along the text and the specifications set the measurement conditions. For Eddy Current, which is a contact technique, the main limit is the necessity to have a flat surface that can host the instrument head. For non-contact imaging techniques (MP and OCT) the constraint is the surface flatness related to the focal depth (set by the objective focal length).

How do the authors expect to find correlations between the original coating and patterns made in the laboratory? Visually or using machine learning methods?

The samples, which were developed in the framework of a wider project, do not intend to reproduce any specific pattern. The samples provide a sufficiently wide typology of coatings (both for their composition and thickness/morphology) that could allow us to set and test a measurement protocol that can be effectively applied to real cases.

The goal of the present paper is a proof of concept of the usefulness of the presented techniques for the non-invasive in situ analysis of bronze artworks. In specific, we want to demonstrate the suitability of the multimodal approach to chemically and physically characterize different coatings.

To clarify this point, in accordance to the reviewer 3 comments, we have added a table with the comparison of the instruments’ performance.

Page 3, what kind of abrasive paper (granulation) was used to prepare the surface, and was the surface degreased?

We added this information in the 2.1. Mock-ups simulating historical reconstructions and Renaissance relief paragraph

In Figure 2, the markings a, b, ...., and g are missing.

DONE

Table 1 should be narrowed by reducing the width of the second, third and fourth columns.

DONE

In the references, in [26], the title of the journal should be in abbreviated form. The title of the article is missing in {33]. In [35] should be Wiley. Many places are missing spaces.

We have corrected all these issues in the references.

Comments on the Quality of English Language

I have no comments, the text is understandable.

Reviewer 3 Report

Comments and Suggestions for Authors

The paper studies the implementation of patina on historical bronze applied to small-size statues. However, there are several things that could be done to improve the paper.

1. The formulation and application of patina have been discussed. This paper is also focused on the non-invasive characterization of coatings. It would be better if authors could provide an image or schematic on how to prepare samples for each technique. A schematic of the best protocol for patina fabrication on such artwork should be provided. Thus, reader can visualize clearly.

2. A table of advantages and disadvantages of each non-invasive method would be great for comparison.

3. It would be better if you could provide data on aging materials in this paper since it would increase the novelty and impact of the paper.

Author Response

The paper studies the implementation of patina on historical bronze applied to small-size statues. However, there are several things that could be done to improve the paper.

Thank you for reviewing our manuscript and for your comments. Here below you can find our replay.

1. The formulation and application of patina have been discussed. This paper is also focused on the non-invasive characterization of coatings. It would be better if authors could provide an image or schematic on how to prepare samples for each technique. A schematic of the best protocol for patina fabrication on such artwork should be provided. Thus, reader can visualize clearly.

The description of the patina fabrication of the mock-ups (ingredients, process) is already included in the Appendix (Table 3)

2. A table of advantages and disadvantages of each non-invasive method would be great for comparison.

Thank you for this suggestion. We included a new table (Table 2) in the text.

3. It would be better if you could provide data on aging materials in this paper since it would increase the novelty and impact of the paper.

This is a key point of the project. The samples were not aged yet, this will be the follow up of the present work, as specified in the introduction (page 2, line 31).

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

I am satisfied with the changes made by the authors and I think that the manuscript could be published, but I think that the References still need to be sorted out:

1. The style of citation of references is not consistent with the requirements of the Coatings journal. It should be: the author's surname, the first letter of the name, and so on.

2. The names of journals are written in different ways:

- as a dotted abbreviation, e.g. Stud. Conserv.

- as an abbreviation without dots, e.g. Herit Sci

- as a full name, e.g. Journal of Cultural Heritage

This should be standardized according to the requirements of the Coatings journal, i.e. as an abbreviation with dots.

Reviewer 3 Report

Comments and Suggestions for Authors

The authors have addressed all comments.