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  • Stefania D’Ottavio1,
  • Angelo Tatì2 and
  • Loretta Bacchetta2
  • et al.

Reviewer 1: Anonymous Reviewer 2: Jorge Alberto Duran Suarez Reviewer 3: Anonymous

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The review comments have been uploaded.

Comments for author File: Comments.pdf

Author Response

1.The manuscript mentions multiple methods, but none of them are supported by on-site testing photographs.

Thank you for pointing this out. We have improved the methods description and included some explanatory images (Materials and Methods section, Figures 2 and 3, Tables 1,2 and 3)

2. Figures 2–5 have poor image quality and appear very blurry. Please replace them with high-resolution versions.

Sorry for the inconvenience, high quality figures are now included in the manuscript.

  1. For all tables, the table title should be placed above the table.

Thank you for the advice, the legends were moved above the tables.

  1. In Lines 59–68, the numbering style should be revised from “1, 2, 3” to “(1), (2), (3)”.

Thank you for the suggestion, the numbering style was revised

  1. At the end of the Introduction, the authors did not clearly highlight the research gap or shortcomings of existing studies, nor did they emphasize the innovation of the present work.

Thank you for pointing this out. The non-contact probe technique has been rarely applied in Cultural heritage materials. ENEA laboratory has developed an automatic system for ultrasonic mapping using non‑contact probes for examining samples that cannot be inspected with immersion-in-water or contact ultrasonic techniques. The technology consists of a high‑energy ultrasonic pulse generator, a band‑pass receiver, and U.S.-patented probes that enable the transmission of ultrasonic waves through air. This technique, also known as air‑coupling, does not require any additional transmission medium—such as gel or other liquids—to provide mechanical continuity. The distinctive feature of this system lies in the combination of a point-based setup, represented by an ultrasonic probe, and a precision positioner capable of moving along Cartesian axes, consisting of linear guides that displace the ultrasonic probe One of the author (A. Tatì) applied and improved the use of the  probe (Pagliaroli T., Pagliaro A., Patanè F, Tatí A., Peng L., Wavelet analysis ultra-thin metasurface for hypersonic flow control, Applied Acoustics, Volume 157, 2020,107032; Luprano, V.A.M., Tundo, A., Tatì, A.,Grinzato E., Marinetti, S., Bison, G,  (2022). Non Destructive Defect Characterization in Civil Structures Reinforced By Means Of FRP, 9ht European Conference on NDT_Berlin 2006; Tatì A. I sistemi di mappatura non distruttiva UT,  2022, EAI 10.12910/EAI2021-099). Therefore, we improved the reference section and modified the introduction section, according to this suggestion

  1. The study is largely qualitative, with insufficient quantitative analysis. The authors are encouraged to address this issue in the Discussion section, or at least acknowledge the limitations of the

Thank you for pointing this out. The discussion section was modified, and the Conclusion section was added.

  1. Ultrasonic testing is already a relatively mature technique. The authors are advised to refer to the following relevant study: two-step detection of concrete internal condition using array ultrasound

We agree that ultrasound testing is a quite mature technique, as we acknowledged in the paper. Since the paper is focused on the Ultrasonic technique that uses non-contact probe, we have modified the introduction and reference sections to point this out. Thank you for suggesting this study about  deep‑learning approaches  combined with ultrasonic technique. The study  suggested was quoted in lines 413-417  as a futher development of the work.

  1. It is suggested to consider adding microstructural analysis and long-term aging tests.

This is a very interesting suggestion: we consider including these features in the future development of the work

  1. The proposed detection method is based on laboratory samples. Its effectiveness for real samples under complex environmental conditions is unclear. The authors are encouraged to supplement the study with validations using real-world samples or more complex simulated samples.

Thank you for the suggestion. We acknowledge that tests on replica samples alone are not sufficient; however, our current efforts focus on developing suitable methods for examining fragile surfaces and objects. In the next step, we intend to conduct tests on real case studies. We added this point in Conclusion section.

  1. Although the manuscript emphasizes the “complementarity” between ultrasonic testing andp eel-off testing, it does not propose an integrated framework or metric for multi-source data

Thank you, this is an excellent suggestion. We will consider the possibility of developing an evaluation index that integrates all relevant variables

 

  1. The quality of English writing should be further improved.

Thanks for the note. We have worked on improving the quality of the English.

  1. Many references cited at the end of the manuscript are relatively old. The authors are advised to include more recent and high-quality journal publications.

Thank you for the suggestion. Some of the “outdated” references are in fact foundational papers in the field, and they continue to be cited because they established the core principles on which much of the subsequent research is built. Anyway, the bibliography has been updated with more recent references.

 

Author Response File: Author Response.docx

Reviewer 2 Report

Comments and Suggestions for Authors

Dear Authors, the study entitled Advanced Ultrasonic Diagnostics for Restoration: Effectiveness of Natural Consolidants on Painted Surfaces, is highly relevant to the field of art materials and heritage conservation and restoration. Overall, the study appears somewhat overly optimistic, as the results do not strictly correspond to the discussions and conclusions presented in this research work. It would be highly advisable to include a graphical abstract (general) and, in some cases, a flow chart. Tables and figures are missing that would complement the work, given the large number of pigments, binders/techniques, and consolidants used. Images of the materials used are also lacking, as well as their colorimetric notations, each presented independently of the agglutinated mixture, whether consolidated or not.

Below are several points that could facilitate understanding and improve the quality of the study:

  1. It would be highly beneficial to include a graphical abstract or a flow chart clearly illustrating the entire experimental process developed.
  2. Provide a detailed table specifying the physicochemical characteristics, manufacturer, and brand (where applicable) of the Arabic gum, Funori, and Nopal (Opuntia ficus-indica), along with bibliographic references regarding their advantages and disadvantages in heritage conservation and restoration.
  3. In the Materials and Methods section, include a diagram showing the preparation process of the replicas for the different techniques, indicating the support and its layers.
  4. Include a table listing the pigments used, with their denomination, Color Index, and, if possible, some chromatic coordinates (e.g., CIELab 1976) for the pigments used.
  5. Provide a table detailing the physical and chemical properties of the binders used in the study, along with their colorimetric notation (e.g., CIELab 1976).
  6. Specify the nature of the mortars supporting the tiles, whether made with air lime or hydraulic lime, mixtures, percentages, aggregates, and additives, preferably in a table.
  7. Lines 101–104: How was complete carbonation of the mortars ensured? Which analytical method was used to determine full carbonate presence? Is it merely an estimation that three months in a climate chamber guarantees complete carbonation? What type of binders were used in the mortars to indicate full polymerization? Please include this information in a content table.
  8. Colorimetry results: Provide at least the reference pattern underlying ΔE, i.e., the L*, a*, b* values of the baseline color (prior to consolidation).
  9. Lime tempera and Arabic gum show a mean value of 0.7 and a standard deviation of 1.3—this appears inconsistent.
  10. Egg tempera with all three consolidants yields the same mean and standard deviation; particularly with Funori, the mean is 3.2 and the standard deviation is 5. Does this imply that the difference is visible to the naked eye? Please justify and clarify these terms.
  11. Peeling Test – Scotch Tape Test: In Figure 2, the quantities detached are unclear. Provide a table or adjust the Y-axis scale in graphs a, b, and c.
  12. Section 3.3 Automated Ultrasonic Mapping System: Why are these results referred to as “mapping”? The text emphasizes the importance of mapping, yet no graphical mapping of the studied samples is presented.
  13. In Figure 3, indicate what the Y-axis value represents: microseconds? Ultrasonic velocity in m/s? This must be specified.
  14. Regarding ultrasonic results and discussion: Please elaborate on the greater influence of pigments compared to binders. How was this detected? What is the underlying reason? Include bibliographic references supporting this discussion.
  15. Contact angle: Provide frames or images of the measurements performed with each consolidant relative to the binders.
  16. In Figure 5 (contact angle), include a scale clearly marking the angle at 90°, as this value indicates hydrophobicity.
  17. It appears that before consolidation, egg-based and egg-oil binders already exhibit values equal to or greater than 100°, implying inherent water repellency. However, after consolidation with Opuntia, Arabic gum, and Funori, hydrophobicity is null or decreases. Why does this occur? Please justify with references where applicable.
  18. What explains the increase in hydrophobicity for Lime and Lean cases, while in the other two binders it decreases in all instances? Discuss and justify these aspects.
  19. The Discussion section is insufficiently clear. It should expand on certain aspects revealed by the study and attempt to explain the heterogeneity of results, particularly in ultrasonic and contact angle tests.
  20. Include a structured Conclusions Section, highlighting the major and minor achievements of the study.

Kind regards

Author Response

  1. It would be highly beneficial to include a graphical abstract or a flow chart clearly illustrating the entire experimental process developed.

Thank you for the suggestion. The graphical abstract was uploaded to the platform.

  1. Provide a detailed table specifying the physicochemical characteristics, manufacturer, and brand (where applicable) of the Arabic gum, Funori, and Nopal (Opuntia ficus-indica), along with bibliographic references regarding their advantages and disadvantages in heritage conservation and restoration. In the Materials and Methods section, include a diagram showing the preparation process of the replicas for the different techniques, indicating the support and its layers. Include a table listing the pigments used, with their denomination, Color Index, and, if possible, some chromatic coordinates (e.g., CIELab 1976) for the pigments used. Provide a table detailing the physical and chemical properties of the binders used in the study, along with their colorimetric notation (e.g., CIELab 1976). Specify the nature of the mortars supporting the tiles, whether made with air lime or hydraulic lime, mixtures, percentages, aggregates, and additives, preferably in a table.

Thank you for these comments. We acknowledge that our previous description was overly concise, compromising clarity. We have therefore revised the entire Materials and Methods section, providing additional details regarding both the methodologies employed and the materials used in the preparation of the replica tiles. Table 1 reports the preparation process of replicas for different techniques; Table 2 was added on the physicochemical characteristics, advantages and limitations of the Arabic gum, Funori, and Opuntia ficus-indica mucilage. Figure 2 describes Ultrasonic mapping Software, showing the C-scan maps (a and b) and the amplitude of the reflected signal C. Figure 3 depicts the peeling test and contact angle techniques. In supplementary material 4  are  provided  the data about the pigments.

 

  1. Lines 101–104: How was complete carbonation of the mortars ensured? Which analytical method was used to determine full carbonate presence? Is it merely an estimation that three months in a climate chamber guarantees complete carbonation? What type of binders were used in the mortars to indicate full polymerization? Please include this information in a content table.

Agree. We did not measure the carbonatation by  analytical method. The phrase was changed accordingly

  1. Colorimetry results: Provide at least the reference pattern underlying ΔE, i.e., the L*, a*, b* values of the baseline color (prior to consolidation).

Thank you for the suggestion: the complete data set  with L*, a*, b* values was added to the supplementary materials 5

  1. Lime tempera and Arabic gum show a mean value of 0.7 and a standard deviation of 1.3—this appears inconsistent. Egg tempera with all three consolidants yields the same mean and standard deviation; particularly with Funori, the mean is 3.2 and the standard deviation is 5. Does this imply that the difference is visible to the naked eye? Please justify and clarify these terms.

The difference perceptible to the naked eye is determined by the absolute value,, not by the       standard deviation. In the case of funori, the standard deviation is higher because numerous   spots and superficial whitening were present; consequently, the distribution of the replicates          was, understandably, irregular. A comment was added in lines 370-371.

 

  1. Peeling Test – Scotch Tape Test: In Figure 2, the quantities detached are unclear. Provide a table or adjust the Y-axis scale in graphs a, b, and c.

Thank you for the suggestion, the Y-axis  scale was adjusted

  1. Section 3.3 Automated Ultrasonic Mapping System: Why are these results referred to as “mapping”? The text emphasizes the importance of mapping, yet no graphical mapping of the studied samples is presented.

Thank you for pointing this out. ENEA laboratory has developed an automatic system for ultrasonic mapping using non‑contact probes for examining samples that cannot be inspected with immersion-in-water or contact ultrasonic techniques. The technology consists of a high‑energy ultrasonic pulse generator, a band‑pass receiver, and U.S.-patented probes that enable the transmission of ultrasonic waves through air. This technique, also known as air‑coupling, does not require any additional transmission medium—such as gel or other liquids—to provide mechanical continuity. The distinctive feature of this system lies in the combination of a point-based setup, represented by an ultrasonic probe, and a precision positioner capable of moving along Cartesian axes, consisting of linear guides that displace the ultrasonic probe. Tatì A. I sistemi di mappatura non distruttiva UT  2022, EAI 10.12910/EAI2021-099  

Threfore, we added figure 2 in M&M section and provided a more detailed explanation of the method.  

 

  1. In Figure 3, indicate what the Y-axis value represents: microseconds? Ultrasonic velocity in m/s? This must be specified.

Thank you for pointing this out. The ultrasonic probe generates a low-level electrical signal in the millivolt range, which is amplified to volt-level before digitization. The amplified waveform, which is bipolar (positive and negative), is sampled by an 8-bit analog-to-digital converter (ADC) with a range from −128 to +127. These digitized values are dimensionless integers and do not represent voltage directly. For image mapping, the absolute value of the waveform is computed, and for each pixel, only the maximum absolute amplitude within the acquisition window is retained. This value is then normalized to a scale from 0 to 128, meaning each pixel represents a relative amplitude index rather than a physical voltage. It is critical to note that quantitative comparisons between different samples or between pre- and post-treatment conditions are only valid if all acquisition parameters remain unchanged. These include gain, acquisition time, number of points, averaging, pulse type, probe model, and instrument model. Any variation in these factors alters the system response and invalidates direct amplitude comparisons.

For this reason, the Y-axis for Ultrasonic signal reported in graphics is a pure number. We added the details to the legend.

  1. Regarding ultrasonic results and discussion: Please elaborate on the greater influence of pigments compared to binders. How was this detected? What is the underlying reason? Include bibliographic references supporting this discussion.

Agree. This was an unexpected result that needs to be further investigated in the future development of the work .

  1. Contact angle: Provide frames or images of the measurements performed with each consolidant relative to the binders. In Figure 5 (contact angle), include a scale clearly marking the angle at 90°, as this value indicates hydrophobicity.

Thank you for the suggestion. We added the scale marking the angle at 90°, and a new Figure 3 showing two images of contact angle technique

  1. It appears that before consolidation, egg-based and egg-oil binders already exhibit values equal to or greater than 100°, implying inherent water repellency. However, after consolidation with Opuntia, Arabic gum, and Funori, hydrophobicity is null or decreases. Why does this occur? Please justify with references where applicable. What explains the increase in hydrophobicity for Lime and Lean cases, while in the other two binders it decreases in all instances? Discuss and justify these aspects.

We agree with the reviewer, but we reported the results that were observed Perhaps the consolidants partially dissolved hydrophilic components of the formulations, making the surfaces more porous and therefore more wettable? Or, after consolidation, the surface somehow became ‘cleaned’ of any dust (often hydrophobic), so the surfaces were a bit more hydrophilic after consolidation.

 

  1. The Discussion section is insufficiently clear. It should expand on certain aspects revealed by the study and attempt to explain the heterogeneity of results, particularly in ultrasonic and contact angle tests.Include a structured Conclusions Section, highlighting the major and minor achievements of the study.

Thank you for the suggestion: Discussion was extended and Conclusion section was added to the text

Kind regards

 

 

 

 

Author Response File: Author Response.docx

Reviewer 3 Report

Comments and Suggestions for Authors

The manuscript submitted for review is valuable. As a scientist, I am involved in ultrasound research mainly in the automotive industry, and I found the presented research area not only interesting but also very valuable. I believe that the authors have done a good job.

The topic of the work has been chosen correctly. The keywords have also been chosen correctly. I believe that the abstract is well written, although it would be worth adding the most important numerical results.

The submitted article concerns the use of non-contact ultrasonic diagnostics to assess the effectiveness of natural consolidants used in the conservation of wall paintings. The authors address an important and topical scientific problem, combining issues of cultural heritage protection, non-destructive testing methods, and sustainable, environmentally friendly conservation materials.

The main advantages of the article include:

- The innovative use of an automatic ultrasonic mapping system to assess the consolidation of paint layers on plaster,

- A well-designed research methodology, including a comparison of non-destructive methods (ultrasound, colorimetry, contact angle measurement) with a semi-destructive test (peeling test),

- A valuable comparative analysis of three natural consolidants (gum arabic, Funori, and Opuntia ficus-indica mucilage),

- A detailed and logical interpretation of the results, including a critical assessment of apparent contradictions between the results of ultrasonic testing and the peel test.

The article is of a high standard and makes a significant contribution to research on non-destructive diagnostics in the conservation of works of art. The work is original, well-documented, and can serve as a reference point for further research in this area.

I believe that the authors have done a good job.

Comments for author File: Comments.pdf

Author Response

Thank you very much for your thorough and thoughtful evaluation of our manuscript. We sincerely appreciate your positive assessment of our work and your recognition of the relevance of combining non-contact ultrasonic diagnostics with the study of natural consolidants for wall painting conservation.

We are grateful for your comments highlighting the strengths of our methodology, the comparative analysis of the consolidants, and the interpretation of the results. 

Once again, thank you for your constructive feedback.

Kind regards

 

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

I have no other comments.

Author Response

We are very grateful for your suggestions, which helped make the paper more understandable and improved its overall quality.   Very kind regards,   Chiara Alisi

 

 

Reviewer 2 Report

Comments and Suggestions for Authors

Dear authors, thank you for the effort made to provide an improved text and a stronger academic approach to the submitted article. The corrections and discussions included in the comments are coherent and scientifically well justified. I would like to reiterate that the new additions to the text truly contribute to a significant improvement from both scientific and technical perspectives. Sincerely,

 

Author Response

Thank you so much for the suggestions, we really appreciate your contribution to the good outcome of this work.

Very kind regards,

Chiara Alisi