What You Clean Is What You Get: A Novel Chemical Cleaning Technique and the Interpretation of Corrosion Products Found in Late Roman Copper Alloy Coins Retrieved from the Sea
Round 1
Reviewer 1 Report (Previous Reviewer 3)
The authors improved the manuscript content by sufficiently following the reviewer's suggestions
Reviewer 2 Report (Previous Reviewer 2)
After the resubmission the paper was greatly improved.
Reviewer 3 Report (New Reviewer)
General Comment:
Overall, this paper is an appropriate contribution in terms of content and methodology. Its interest is very relevant for the knowledge of the conservation of archaeological artefacts from underwater provenance.
Overall the article is well formulated and covers the objectives set out by the authors and mentioned in the body of the text focused on the cleaning process of ancient copper alloy objects from marine environments, ensuring a novelty contribution to the field. Furthermore, I warmly recommend it for publication in MDPI Heritage.
Some observations of a formal nature:
The bibliography lacks some relevant publications directly related to the conservation of copper alloy in archaeological artefacts:
*Casaletto, M., Caruso, F., De Caro, T., Ingo, G., & Riccucci, C. (2007). A novel scientific approach to the conservation of archaeological copper alloys artefacts. In Metal 07. Triennial meeting of the ICOM-CC Metal Working Group (No. 2, pp. 20-25). ICOM.
**De Viviés, P., Bayle, M., Houssin, P., Memet, J-B. (2021) Science, part of DNA of conservation. In Sand, A. Aragon,E. and Rodriguez, J. (Eds.). #ISCUA2019. Proceedings. The 1st International Symposium of Conservation for Underwater Archaeology. Universo de Letras. Madrid.
*** MacLeod, I. D. (1987). Conservation of corroded copper alloys: a comparison of new and traditional methods for removing chloride ions. Studies in conservation, 32(1), 25-40.
This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.
Round 1
Reviewer 1 Report
No suggestions
Author Response
Please see the attachment.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
The research is interesting and deals with a theme that is still very open but above all innovative, and which concerns the conservation of finds / objects that come from the marine environment.
The work can be improved, there are some unclear aspects but it is suitable for Heritage journal. A broader overview of the discovery context, the wreck, should be made. Some considerations and suggestions are below:
Abstract
Line 17 – please change "while incurring minimum damage to the surviving metal" with "limiting damage to the.....".
Line 20 - Did the authors mean "incoherent materials" when they write “bulk”?
Line 20 - Change irregular with different
Line – 20-22 -In this sentence is not very clear if this was how the coins looked when they were recovered from the sea. Authors need to rewrite the sentence and make it more understandable
Introduction
Line 37 - Please change “a newly-devised chemical technique hitherto applied to only one specimen. “ in “..a chemical technique of new conception so far applied to a single specimen.”
LINE 42 – Plaese add a reference after “copper alloy”
Line 55 - Change “will comprise” with “ will covered by…”
Line 56 What the authors mean with “impede effort to detremine…”? Perhaps they mean that the presence of surface residues does not allow for an accurate scientific investigation? Please specify
Line 68 - 1H3PO4:5CH3COOH:4HNO3 (PAN). peroxyacetylnitrate? please specify in full why it is the first time it appears in the text
Materials and Methods
Site and Coins
I believe that the description of the site, in this case, the MMB shipwreck, should be in a separate paragraph, before the materials and methods. Something like "The underwater site" .... where attention is paid to the historic/archaeological context of discovery and to the importance of the research which, for several years now, has been involving underwater finds/objects and their conservation/protection. In a journal like Heritage, the authors must also give importance to the historical context and not only to the scientific impact of the research. In this regard, I suggest some references to be taken into consideration related to "cultural heritage", not just coins, from the marine environment and their studies and conservation strategies that will allow for a global overview of the problem of submerged finds/objects/artefacts (Gregory, D.J., Manders, M. Best practices for locating, surveying, assessing, monitoring and preserving underwater archaeological sites(2015) SASMAP Guideline Manual 2.; DOI 10.1016/j.matdes.2020.109278 Definition of analytical cleaning procedures for archaeological pottery from underwater environments: The case study of samples from Baia (Naples, South Italy); Davidde Petriaggi, B.Methods and strategies for the conservation and museum display in situ of underwater cultural heritage (2004) Archaeol. Maritima Mediterr, 1, pp. 137-150; Evaluating the use of laser in analysis and cleaning of the islamic marine archaeological coins excavated from the red sea.)
Line 92 - 103 - Based on the 53 coins found in the wreck, why did the authors study 15 of them?Line 110 - When the authors write "reveal further information" please specify what. Perhaps the iconography of the coins?
Figure 1 The caption of the figure is unclear. It should be specified if some images are front/back, is this correct? Moreover, there are 38 coins in all. Why? Please clarify better.
Line 115 When the authors write “The concretion layer could not be removed in some areas”, what did they mean with “concretion”?”. From the images it is not clear what the type of concretion is. Sediments/minerals? just patina? benthic microorganisms?
Analytical Methods Line 128 The term "cadre" sounds inappropriate, please replace with something like "different or several analytical methods
Results
LINE 165 What do the authors mean with “dark blue patches”?
Table 1 In the caption, rather than "concretion coating" it would be better to "concretion layers", as in the text. Coating seems more to refer to a coating of another nature, such as a chemical coating
Which database was used to compare the Raman bands? please indicate it as a bibliographic reference
In figure 6, the authors should overlay the Raman spectrum of the identified minerals (quartz, sanidine, etc.) or perhaps it would be better to talk about quartz and feldspathic sands.
Line 378 Please consider the previous comment, perhaps it is more appropriate to talk about sediments or quartz and feldspathic sands
Line 341 and 379 - When authors talk about plastic deformation, they should add references, or give a greater explanation of the process (Characterization of bronze Roman coins of the fifth century called nummi through different analytical techniques; Residual stress in struck and cast coins https://doi.org/10.1784/insi.2020.62.3.139)
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 3 Report
The work presented by the authors is certainly interesting. However, I have suggestions for authors to improve the manuscript and make it interesting for a wider audience.
-In the introduction, the authors state that sandblasting fails in
removing all the concretion and therefore they developed a chemical method. However, mechanical cleaning to clean coins which consists of scraping and brushing is the preferred method of cleaning any antique coin as well retain its patina. There is not only sandblasting but different mechanical methods that use different types of tools. I ask the authors to explain in more detail why cleaning the 15 coins carried out with the mechanical method was not enough. What in particular made you say that the coins weren't clean enough?
-Has the chemical cleaning method of the coins you proposed been tested on specimens before? If so, can you provide preliminary results?
-Specify better what you have been able to clean with the chemical method that the mechanical method cannot do.
The patina is known to protect coins from rotting. With the chemical method, the patina is destroyed. Have you ever thought of any method to restore a protective patina after cleaning the coins?
Regarding the structure of the manuscript:
please move lines 66 to 72 from the introduction to the materials and methods section.
Author Response
Please see the attachment.
Author Response File: 
Author Response.docx
