Study of the Effects of Cu/Cu-Zn Alloy Components Adjacent to Wood in Historic Architecture: Surface Performance Changes by Artificial Wood Degradation

Round 1

Reviewer 1 Report

Dear Authors, the article could be of interest but I suggest to have a more look among the differences of the species, and there are some major concern related to the FTIR analysis. Please have an overlook also the the references I suggested in the text and the references on waterlogged wood, they can be of interest for you.

English must be improved and figures also are placed not symmetric in the text. 

Further comments in the article 

Comments for author File: Comments.pdf

Author Response

Thanks very much for your precious advice.
Firstly, the Sugi (Cryptomeria japonica) and Keyaki (Zelkova serrata) were selected because these species are the typical softwood and hardwood species used in historic wooden architecture in Japan. By which the authors want to prove if the generation of oxalate is a common phenomenon regardless of wood species. Besides, the FTIR analysis was used for tracking the generation of oxalate in this study. The different FTIR spectral changes have been discussed in our previous works. We uploaded the articles in case you may have some interest.
Secondly, the references of iron contaminated waterlogged wood are very important for this study, some are listed in the new revision.

Thirdly, the English-editing service provided by MDPI was applied.

And we will consult with the editor to solve the layout problems.  

Further replies to comments in the article. 

Author Response File: Author Response.pdf

Reviewer 2 Report

Dear Authors,

your research is interesting and fitting the aims of the journal. However some aspects should be reviewed and analysed. The mechanical tests were carried out by means of both static and dynamic method. For the static tests you should pay attention to the difference between stress/load, strain/displacement and MOE/stiffness. The tests you performed (localized compression) produce load/displacement and stiffness data because the contact area is not a constant surface. In addition, possibly, for that test it is better to use the term "hardness test" which better describe the test itself. However, by definition the hardness test provides local data; thus, you should clarify how the local effect (of the early/late wood for insatnce) has been taken into consideration. Indeed, the results show a large variability for the transversal mechanical tests which could be explained by local measurements. It would be useful to know how many specimens were tested for each category. In general, the results from the mechanical tests (both static and dynamic) show a large variability which make difficult to interprete the stiffness behaviour of treated Sugi and for Zn-treated-Keyaki. Also, it would be useful to specify which statistic you used to analyse the data.

Here below some detailed comments:

• line 34: which is the previus work you refer to? citation 1?
• line 162-163: this is the linear limit, not the elastic one;
• figure 10: layout problems;
• figure 13a: the chose scale make impossible to read correctly the graph.

Thank you for your work.

Author Response

Thanks very much for your precious suggestions.

In this report, the authors will reply to the comments point to point. The reviewer’s comments are in grey, the authors’ replies are in black.

Author Response File: Author Response.pdf

Reviewer 3 Report

Please find my comments and suggestions in the attached file.

Comments for author File: Comments.pdf

Author Response

In this report, the authors will reply to the comments point to point. The reviewer’s comments are in grey, the authors’ replies are in black.
The manuscript has been restructured. The descriptions dealing with colour changes in every section are rearranged to the later part after descriptions dealing with other evaluations. And some descriptions have been rephrased. 

Author Response File: Author Response.pdf

Reviewer 4 Report

The paper “Study of the Effects of Cu/ Cu-Zn Alloy Components Adjacent to Wood in Historic Architecture: Surface Performance Changes in Artificially Degraded Cu(II)/Zn(II) Impregnated Wood” is potentially interesting and could have practical application in the conservation of cultural heritage architectural elements, but I think that the paper needs revision before being accepted for publication in the journal Coatings.

In general, I suggest an English revision of the text, possibly by a native speaker.

Moreover, I think that the title must be changed because the authors did not make tests on historical Architecture but only on laboratory samples, so I suggest to modify the title, for example: Surface Performance Changes in Artificially Degraded Cu(II)/Zn(II) Impregnated Wood samples to simulate Historic Architecture real cases.

Other comments:

• The first sentence in the abstract lack of the verb
• The second sentence in the abstract, i.e. “Following the field investigation results of Cu/Zn elements and fine particles of copper/zinc oxalate hydrate detected in the whitened wood, this study established the model experiments focused on studying the effect that Cu(II)/Zn(II) ions have on wood were performed by periodically evaluate Sugi (Cryptomeria japonica) and Keyaki (Zelkova serrata) plate samples under exposure conditions of 60°C and RH 90%, observing 1) the state of metal oxalates in the wood tissue(FTIR-ATR, SEM-EPMA), 2) the whiteness of the wood surface(colourimetric measurements), and 3) the mechanical performances of wood(compression test and flexural vibration tests).”

apart that is excessively long, it has various errors … ions have on wood were performed …?? … by periodically evaluate … it should be by periodically evaluating.

Abstract must be re-written by better defining the aims, the methodology used and a synthesis of the results, even if the results of the study seem not being definitive and validated.

• Introduction, line 33: architectures instead of architects
• Figure 1. The images in the figure 1 are too low in resolution, please supply photos of higher quality. Also the text in the images is at low resolution.
• Introduction, lines 53-60: “To verify the processes of how metal ions affect wood and ultimately result in the generation of metal oxalates, a model experiment was carried out by authors with wood powders of Sugi (Cryptomeria japonica) and Keyaki (Zelkova serrata), with different levels of Cu(II)/Zn(II) ion contents (percentage of dry weight: 0.00%, 0.05%, 0.50%, 2.50%), exposed to 60°C and relative humidity (RH) of 90%. The results of IC, HPLC and FTIR analysis of degraded samples proved a significant proportion of oxalate ions and monosaccharides, generation of metal oxalates, especially in the cases with 2.50% Cu content.”

This experiment is referred to a previous work? It is not clear from the text. Probably ref [9].

Moreover, I did not find ref [1] (probably the published paper is in the original language of the authors, and I cannot find it).

Did the authors publish their previous results in [1]?

• Materials and Methods, lines 89-91: “The wood plate samples were exposed under 60℃ and RH 90%, conditioned by a constant climate cabinet (SH-221, ESPEC, USA), and the samples were evaluated every 30-d.”

The exposure of the samples under controlled conditions was performed after impregnation with metal ion solutions? right? So, I suggest to move this part after the section Preparation of the Samples.

• Materials and Methods: Table 1 is not clear. The lines Cu(II) Content (wt%: mg/mg) Zn(II) Content (wt%: mg/mg) should be shifted down above the mean row.
• Paragraph 2.2.3, Colorimetric Measurements: please explain how you calculated the colour changes and how you reported the results.
• Paragraph 3.2, lines 222-224: “The appearance of additional particles with brighter tones scattered in the wood tissues in images of samples with higher Cu(II) content, since 30-d exposure.”

This sentence is not clear, the verb lacks. Please correct. Which image is it referred to?

• Page 9, lines 231-232: “In x 10,000 magnification morphology of the particles in S/K-B-Cu 3 at different exposure stages, the particles appear as aggregations of flake-like crystals.”

The sentence needs revision, … of the particles …, the particles …

• Page 11: please check the caption of figure 10
• Page 11, lines 276-279: “The Zn(II) contained samples show similar trends. In Cu(II) contained samples, increased tendencies of L* values appear to be positively correlated with Cu(II) content, while for a* and b* the correlation seems negative.”

The authors use Zn(II) contained samples and Cu(II) contained samples, but it is not correct. It should be: samples containing Zn(II) or samples containing Cu(II)

• Paragraph 3.4. For me this part is completely unclear. The authors affirm that “None of the wood plate samples show visible whitening discolourations after the 120-d exposure”. But, in the figure 11 the changes (%) appears high and significant, in some cases.

“In Cu(II) contained samples, increased tendencies of L* values appear to be positively correlated with Cu(II) content, while for a* and b* the correlation seems negative.”

Seems or is?

Also in this case you must better explain the results. What do you mean with: … while for a* and b* the correlation seems negative?

Probably, I suppose, you would like to say that the a* and b* parameters changes decrease with the increase of Cu(II) concentration, whereas the L* changes increase.

“In the case of S-B-Cu 3, the L* is most pronouncedly elevated, and the increases of a* and b* are less significant (Figure 11. a) in comparison with S-B-Cu 2/1.”

Not L* but the change % of it is the highest in respect to S-B-Cu 2/1.

“For Keyaki groups, blank sample K-B-0 shows the decrease in L*, b*, and constant a*. Most of the other metal contained samples show similar or opposite while insignificant changes, and their dependences on metal content are hardly observed. However, it is noteworthy that the parameters' decreases for K-B-Cu 3 are extremely unnoticeable in L*, while quite substantial in a* and b*, by comparison with K-B-0 (Figure 11b)”.

Also in this case, I don’t understand the authors’ comments: insignificant changes? For K-B-Cu 3 I see a change for a* of about -40%!!

The results about colour changes must be revised and, above all, it must be clearly reported how the authors calculated the % changes.

• Page 12, line 289-294: this part needs deep English revision. It is quite incomprehensible. Moreover, the authors must discuss separately the results of Sugi and Keyaki.
• Page 12, lines 297-298: why? It seems to me that also for the slope changes of the stress-strain diagram there are evident differences in results between metal containing and blank samples.
• Page 12, line 298: “The E’ of blank samples are increased after 120-d exposure.”

It should be: The E’ values of blank samples show an increase (or increased) after 120-d of exposure.

• Page 12, line 303: which decreased not is decreased. Later, … The tanδ are increased … The tanδ values increased …or underwent an increase.
• References: please check the format

Author Response

In this report, the authors will reply to the comments point to point. The reviewer’s comments are in grey, the authors’ replies are in black.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Dear Authors,

I would like to thank you for your clear replies to my comments, replies which are satisfactory to me. The English language is also improved.

Author Response

The minor revision has been done.

Thank you very much for your work in the review process of this paper.

Your suggestions have been very helpful in improving this paper.

Reviewer 3 Report

The authors have very much improved the manuscript. The narrative and structuring is much more clear and the phrasing is decent after language check. I recommend the manuscript for publishing. However, I do still have a few comments on the manuscript that should be addressed before publication:

1) Figure 6. The change of absorbance ranges over many orders of magnitude and it is probably justified to use a logarithmic scale here for the y-axis to improve the graph understandability

2) Figure 10. What do the black arrows indicate? Please say in text and/or figure caption.

3) Please indicate clearly in the manuscript text (e.g. in the text describing the figures 6, 10 and 11) how were the error bars which are shown on the figures calculated. Were the error bars calculated as the standard deviation? at what confidence level?

4) Please comment on the huge error bar of S-A-Cu3 of E, the change is given as -24% but according to the error bar it might be between -7% and -43%. Please indicate a possible reason for thus large spread.

Author Response

The minor revision has been done.

The point to point replies to your comments are listed in the revision report.

Thank you very much for your work in the review process of this paper.

Your suggestions have been very helpful in improving this paper.

Author Response File: Author Response.pdf

Reviewer 4 Report

After revision, the paper can be accepted for publication

Author Response

The minor revision has been done.

Thank you very much for your work in the review process of this paper.

Your suggestions have been very helpful in improving this paper.