Chemical Composition, Crystal Structure, and Microstructure of Slags on the Korean Peninsula from the First Copper Production Remains of the 9th Century
Round 1
Reviewer 1 Report
Comments and Suggestions for Authors
Thanks to the Authors for the manuscript submitted for review to the journal Crystals, titled "Chemical Composition, Crystal Structure, and Microstructure of Slags from the First Copper Production Remains of the 9th Century on the Korean Peninsula "!
Relevance of the Work. The study of ancient smelting and metal production technologies, particularly copper, holds substantial significance for comprehending the evolution and formation of regional metallurgical traditions. As the remnants of ancient copper smelting operations on the Korean Peninsula are scarce and inadequately explored, the discovery and investigation of sites such as Jinan Daeryang-ri present a valuable opportunity to fill the gaps in knowledge regarding copper smelting processes in this region.
Scientific Novelty and Practical Significance. According to the authors' claims, their work represents the first comprehensive analysis of copper production-related slags uncovered on the Korean Peninsula. The authors have conducted a thorough examination of the chemical composition, crystal structure, and microstructure of the slags, enabling the identification of these materials as byproducts of the Cu-Fe-S formation stage during the smelting of chalcopyrite copper ore. These findings contribute scientific novelty and further our understanding of ancient copper smelting technologies in the region. Crucially, the publication's significance lies primarily within the context of regional studies, as it does not present any groundbreaking or unique discoveries. The identification of chalcopyrite in the composition is unsurprising, given its inherent density.
Regarding practical significance, the research outcomes hold relevance for reconstructing ancient metallurgical processes and advancing knowledge of copper production history on the Korean Peninsula. The obtained data can be utilized in archaeological investigations.
Strengths and Weaknesses of the Work. It is fair to acknowledge the study's strengths. Firstly, the authors have demonstrated a comprehensive approach, incorporating the analysis of chemical composition, crystal structure, and microstructure of the slags. Analytical techniques such as XRF, XRD, SEM-EDS, and Raman spectroscopy are employed. This approach represents a logical trajectory for the samples' investigation. The authors also compare their results with data obtained from other archaeological sites of copper production on the Korean Peninsula.
However, certain weaknesses are also evident, such as the limited number of samples (only 10 slags) available for analysis. There is a lack of information regarding sample selection methods and their representativeness. Furthermore, the description of the archaeological context and site dating is insufficient. The work lacks information on the state of copper production during that period. It remains unclear whether major production centers were known and, if so, what characterized them beyond the presence of furnaces and waste materials. Perhaps these characteristics are not specified because they do not exist. It would be interesting to hear the authors' thoughts on this matter. Another shortcoming is the absence of a deeper discussion on the technological aspects of the copper smelting process based on the obtained data.
Thus, the material submitted for review requires substantial revision. Comments and possible ways to address the issues are presented below:
In the "Introduction" section:
1. Page 1, Line 38 the thought is abruptly cut off with the statement that slags consist of a certain set of oxides. At this point, it would be appropriate to insert a block of information that orients the reader on the possibilities of slag analysis in more detail. The authors should provide an extensive informative agenda, mentioning the various solutions they found in analyzing the scientific literature related to the topic of the article. This will justify the chosen approach to conducting the research and connect the authors' work with other studies. This information is critically important because archaeometric papers are read not only by multidisciplinary specialists but also by professional archaeologists and historians who have limited understanding of physicochemical methods.
In the "Materials and Methods" section:
2. The material presented in section 2.1 "Description of ruins" may appear more organically if it is moved to the "Introduction" section. Moreover, transferring this text into the structure of the "Introduction" section would allow for a much more precise understanding of the stated research goals and objectives.
3. The material in section 2.1 suffers from a lack of information about the archaeological context and dating of the Jinan Daeryang-ri site. The authors could provide more detailed information about the archaeological excavations, stratigraphy, and collected findings.
4. The authors do not explain the reason for the limited number of samples (10 slags) for analysis. An explanation for the choice of sample quantity should be added, for example, indicating that this was a preliminary selection for initial study, or explaining that a larger number of samples was unavailable due to excavation limitations or the condition of the findings.
5. The sample preparation process for the study is described insufficiently. It remains unclear what tools and equipment the authors used for cleaning. What do the authors mean by the term "surface debris"? The samples were dried and ground into powder, but the method and the achieved dispersion level are not mentioned.
6. The analytical methods and analysis parameters are not described in sufficient detail in the "Materials and Methods" section. What equipment did the authors use for preparing metallographic samples (cutting machine, polishing machine, type of abrasive and suspension grades)? Was sample etching used for the metallographic study? How critical was the procedure of applying a platinum coating to the sample surface for SEM imaging? Why did the absence of this procedure in sample preparation hinder the study? What calibration samples were used for calibrating the equipment for elemental composition analysis (standard or specially manufactured)?
7. The paper does not mention possible sources of error and limitations of the applied methods. The authors could add information about research limitations, in which they could discuss potential sources of error, such as sample heterogeneity, the influence of sample preparation, limitations of the analytical methods used, and possible systematic errors. Acknowledging limitations would increase the credibility of the conclusions.
In the "Results" section.
8. The authors are advised to consider the possibility and necessity of moving some information blocks to other sections:
– p. 6, lines 147-150 – to the Introduction section (see comment #1);
– p. 8, lines 204-205 – to the Introduction section (see comment #1);
– p. 14, lines 267-268 – to the "Materials and Methods" section.
9. For the statement on p. 6, lines 147-150 "...During smelting, copper is primarily extracted from the ore in the form of matte or copper ingot, explaining the limited presence of CuO in the smelting slag...", a literature source from which this statement is borrowed should be provided.
10. In Figure 5, there is no legend with the interpretation of the compound markers on the XRD patterns. The authors should insert a legend indicating the mineralogical name and chemical formula of the compounds.
11. The description of the metallographic study results requires additional clarification with a description of the surface morphology of the studied samples.
12. On the microscopic images in Figures 6, 7, 8, 9, and 10, it is difficult to distinguish the scale bars.
13. In Figures 12, 13, and 14, it is necessary to assign numbering (a, a*, a**, or other) to the three images and coordinate the discussion of their content accordingly.
14. The use of the EDS method for the quantitative determination of carbon is not entirely correct. At the very least, the description of the EDS method does not specifically mention this point. Why do the authors indicate carbon in Tables 4, 5, and 6? The text does not provide any comments on this issue. In this case, the authors may consider removing carbon from the tables.
15. The resolution of Figure 11 needs to be improved to meet the journal's requirements.
16. P. 15, line 281. Correct the negligence in the formatting of the formula (subscripts).
17. The resolution of Figure 16 needs to be increased to meet the journal's requirements.
In the "Discussion" section:
18. In Figure 17, the sources for the SEM images are indicated, but references need to be inserted in the figure caption as well. The scale bars in these images are indistinguishable. In Table 7, references to the sources from which the data was taken need to be provided.
In the "Conclusion" section:
19. Line 418. The term "principal component analysis" is used. This creates an erroneous assumption that this applied statistics method was used in the work, which is not the case. This phrase should be replaced with another synonymous one.
Conclusion
Overall, the presented paper is a valuable contribution to the study of ancient copper smelting technologies on the Korean Peninsula. The authors conducted a comprehensive analysis of slags from the unique archaeological site of Jinan Daeryang-ri. The work has scientific novelty and practical significance for reconstructing ancient metallurgical processes. The strengths of the study include the use of modern analytical methods, illustrative figures, and comparison with other archaeological sites. At the same time, the weaknesses are the limited number of samples, insufficient description of the archaeological context, and insufficient depth in discussing the technological aspects of the copper smelting process.
Considering the comments provided in the review and the suggested ways to address them, the paper can be recommended for publication after revision. Eliminating the indicated shortcomings will improve the quality, informativeness, and significance of the work for the scientific community.
Reviewer's recommendation: Major revision.
Author Response
Please see the attachment.
Author Response File:
Reviewer 2 Report
Comments and Suggestions for Authors
Most of the references are from analysis of local materials related to the processing of copper and bronzes in Korea, I suggest including more current references from 2020, at least until 2023 even though there is little archaeometallurgical information from Korea, there should be specific references to the topic from other countries that could enrich the work.
- Page 5, line138: verify and clarify what they mean by "Quanta 300"; if they are referring to Bruker's "Quantax" tool for X-Ray Spectrometry, which consists of an EDS X-Flash detector and the Esprit software; or if they refer to a SEM brand FEI with models "Quanta" 200, 400, 600, and "Quanta" FEG 250, 650... apparently there are no "Quanta 300" model detectors. I recommend that this paragraph include the name of the software and software module used to obtain EDS oxide-based quantification; it is more common to present the results of EDS as chemical element-based quantification.
- Page 6, lines 154, 155: K2O should be replaced by K2O, ZrO2 should be replaced by ZrO2 and CeO2 should be replaced by CeO2.
- Page 6, line 175: the authors report a single phase of copper oxide (CuO), so copper oxides should be replaced by copper oxide in singular.
- Page 6, line 175: copper slag should be replaced by copper slags in plural. Table 2 should include columns for CeO2, NiO, Cr2O3, Y2O3, and PbO, which are mentioned in the second paragraph on page 6.
- Page 7, line 181: although it is mentioned that the JA-8 sample is amorphous and does not have peaks, it is suggested to append the diffractogram in Figure 5.
- Page 7, Section 3.2 XRD analysis results: the number of JCPDF or ICDD cards corresponding to the crystalline phases identified by XRD is not indicated. Nor is it mentioned in section 2.2 Samples for analysis, the database used to perform qualitative phase analysis by XRD. This information is important because the title of the article mentions "Crystal Srtucture" and little data is shown on the crystal structures identified by XRD. Mention the meaning of A, F, Q, Cr, M1, M2 and M4 in the figure 5.
- Page 8, line 202: the authors mention that Figure 5 shows the results from JA-1 to JA-10, but the results from JA-8 are missing.
- Page 9, line 237: it is not adequate the use of “elevated levels” because the EDS results were processed to report wt% oxide basis; then replace by wt% results.
- Page 14, Section 3.3 Raman microspectroscopy results: the authors do not refer to Figures 11, 12, 13, 14 and 15 in the text of this section; nor do they mention characteristic vibration values of the crystalline phases that they report and should.
- Page 14, lines 277-280: the authors mention that augite and diopside can be distinguished through qualitative analysis using EDS… that is impossible because EDS does not give chemical bond information and although the mapping shows the distribution of the chemical elements, it does not show the distribution of the oxides; there is no way to know what percentage of the total oxygen detected corresponds to each oxide, because it is determined with a software algorithm which considers the elements Ca, Na, Mg, Fe, Al, Ti, Si to be bonded with oxygen atoms. A semi-quantitative analysis of EDS can hardly be considered to represent the stoichiometric composition of a sample such as those analyzed in this work. Therefore, diopside cannot be differentiated from augite by mean of EDS analysis. In addition, in order to consider the EDS analysis to be quantitative, it must be calibrated using a standard that contains the same elements that the samples in known quantities.
- Page 15, figure 13 and 14: It is recommended to indicate which area of the first image was magnified in order to perform point analyses on each figure, as shown in Figure 12.
- Page 17, lines 334 -335: It is repeated in both lines that there is a high amount of sulfur and iron in the copper nanoparticles; these lines should be rewritten.
- Page 17, figure 16: the word "surfide" should be replaced by "sulfide"?
- Page 18, line 387: SO4 should be replaced by SO3.
- Page 18, lines 398-399: “In addition, tin (Sn) was detected in the alloying slags from the Gwanbuk-ri site, with cassiterite identified in the component analysis (see Figure 17, Table 7: C1, C3)”, SnO2 data are not available for this sample and the results from point C-3 are missing in Table 7. As I mentioned before, it is not possible to be sure that you have SnO2 in a slag sample by mean of EDS analysis, you need an analytical technique such as XRD, Raman, FTIR, XPS…
- Page 19, Figure 17: In this work, 10 samples were analyzed, from which sample are the SEM images? The SEM image must be labeled with the sample identification or this information must be written in the figure caption (they appear to refer to the JA-10 sample).
- Page 19, line 416: the word "compounds " is not appropriate for a discussion of X-ray diffraction, this line should be rewritten with the words “crystalline phases”.
- Page 19, lines 420-421: I didn't find 0.1% wt% ZnO in any EDS results table.
- Page 19, line 424: “Compound analysis” should be replaced by “XRD analysis”.
Author Response
Please see the attachment.
Author Response File:
Round 2
Reviewer 1 Report
Comments and Suggestions for Authors
Thank you to the authors for the work done in addressing the remarks and responding to the comments. The paper can be published in its current form.
