Formation of Calcium Oxalate Patinas as Protective Layer on Basaltic Stone Surfaces of 17th Century Raigad Hill Fort, India

Round 1

Reviewer 1 Report

The manuscript is interesting, but it does not absolutely establish the difference between the anthropic or bologic origin of the patinas.

It would be good to improve the microscopic analysis, including petrographic analysis.

 

Author Response

The manuscript is interesting, but it does not absolutely establish the difference between the anthropic or bologic origin of the patinas.

It would be good to improve the microscopic analysis, including petrographic analysis.

Reply

We thank the reviewer for his remarks on this manuscript.

We have tried to improve upon and now incorporated explanations showing biological origin of the patina in the manuscript. We have added further images from the optical microscopic analysis, rock analysis, environmental parameters data etc. to improve the content of the paper, but regret to inform we could not perform petrological analysis. 

Reviewer 2 Report

The work focuses on the very interesting analysis of a superficial patina on a basaltic Indian heritage construction complex. One of the novelties is the substratum on which the patina is developed, which is not very frequently referred in the scientific literature. Various morphological and compositional techniques have been used to analyze the patina samples, concluding it is mainly constitute by calcium oxalates due to the intense microbial activity on the basalts surface, also helping the meteorological conditions they are exposed to.

One of the main areas of weakness is the testability of the hypothesis – in this case, the composition and origin of the patina -, which cannot been proved or demostrated with the obtained results.

Some more specific suggestions are to improve the structure of the manuscript, without mixing in the Introduction section the state of the art of th topic with the specific particularities of the case study, that should be incorporated (and enlarged) later on in a specific section that include the description of the case study. This description, as mentioned, should be separate from Introduction and more consistent: more graphic information is needed (the existing one is few and of bad quality), such as images of the detailed appearance of the basaltic stone, of the surface patina on it, of the microbial development, of the protective effect the patina provides to the stone, of the general and specific degree of conservation/decay, of the location of the samples, of the samples themselves, etc. 

For a more correct and complete Introduction, and for use in the discussion of results (this latter, an aspect that the authors have not addressed in this manuscript), Rampazzi's not so recent paper (Journal of Cultural Heritage 40, 2019, 195-214), an extense and thorough review in which the author processed information on the subject from 349 papers, is indispensable. I highly recommend the authors its reading.

The aim/aims of the research should be addressed; "This paper aims to document the climatic conditions favorable to patina formation" (line 112), is never developed nor documented.

The criteria followed for selecting the samples is never described (are they representative of the whole? what is the location of each of them - height from ground level, for instance?-). The distribution of the patina in the complex is never detailed. Is the patina homogeneously distributed throughout all the surface of the façades - lower and upper parts, all the orientations, both on basalts and mortars, if any? -.

Regarding the techniques used, it should be, as well, explained the criteria for their selection and the purpose of using each of them. As there is no information about the samples (only patinas were sampled? Patinas+substrate? What is the thickness of the patina?), inerpretation of the results is not very clear for the reader. With respect to FTIR results, authors should refer to any scientific paper or database (there are many free in the website, for instance, RRUFF database accounts for FTIR and XRD results). There are some interpretations of existing minerals, but many of the peaks the author refer to in the text cannot be detected. What is the explanation for the muscovite and gypsum presence? In relation to the Optical analysis section, the quality of the images is very poor, and the assigment of some crystals to calcium oxalate has no scientific basis at all. 

In the case of SEM-EDS analysis, the samples should have been analysed not only on the surface, but also in cross-section. In this way it would have been possible to analyse the patina in its full thickness (which is unknown), its homogeneity/heterogeneity, and its relationship to the substrate, all of which can contribute to determining the origin of the patina. The scale of the microscopic images is too large, the technique is not exploited in detail; it is also not known where the EDS analyses shown in table 3 (units?) have been done (they should have been marked on the images); it is also not very scientific to assign mineralogy solely on the basis of morphology, this should always be accompanied by EDS analysis). The statement that the samples are mainly composed of C, O and Ca is not true, as a higher Si, Fe, P and Al content than Ca is observed, none of which is explained or justified.

The basalts should have been analyzed, too. It is very important to know their chemistry and mineralogy, especially the concentration and abundance of Ca-plagioclase, as the authors mention them as Ca source for combining with oxalates. 

Indispensable in this study is the use of polarizing optical microscopy for a petrographic analysis, especially of cross-sections, for determining the structure of the patina and its relationship to the substrate.

Conclusions are poor and not consistent with the results obtained.

References. Besides the indispensable mentioned Rampazzi 2019, there are some others essential for this work, such those authors working/mentioning/referring to patinas on basalts (Columbu et al. 2018, Schiavon et al. 2013, Wilson 2001, Chen et al. 2000, Edwards 1991).

I strongly encourage the authors to improve the paper.

Author Response

The work focuses on the very interesting analysis of a superficial patina on a basaltic Indian heritage construction complex. One of the novelties is the substratum on which the patina is developed, which is not very frequently referred in the scientific literature. Various morphological and compositional techniques have been used to analyze the patina samples, concluding it is mainly constitute by calcium oxalates due to the intense microbial activity on the basalts surface, also helping the meteorological conditions they are exposed to.

One of the main areas of weakness is the testability of the hypothesis – in this case, the composition and origin of the patina -, which cannot been proved or demostrated with the obtained results.

Some more specific suggestions are to improve the structure of the manuscript, without mixing in the Introduction section the state of the art of th topic with the specific particularities of the case study, that should be incorporated (and enlarged) later on in a specific section that include the description of the case study. This description, as mentioned, should be separate from Introduction and more consistent: more graphic information is needed (the existing one is few and of bad quality), such as images of the detailed appearance of the basaltic stone, of the surface patina on it, of the microbial development, of the protective effect the patina provides to the stone, of the general and specific degree of conservation/decay, of the location of the samples, of the samples themselves, etc. 

For a more correct and complete Introduction, and for use in the discussion of results (this latter, an aspect that the authors have not addressed in this manuscript), Rampazzi's not so recent paper (Journal of Cultural Heritage 40, 2019, 195-214), an extense and thorough review in which the author processed information on the subject from 349 papers, is indispensable. I highly recommend the authors its reading.

The aim/aims of the research should be addressed; "This paper aims to document the climatic conditions favorable to patina formation" (line 112), is never developed nor documented.

The criteria followed for selecting the samples is never described (are they representative of the whole? what is the location of each of them - height from ground level, for instance?-). The distribution of the patina in the complex is never detailed. Is the patina homogeneously distributed throughout all the surface of the façades - lower and upper parts, all the orientations, both on basalts and mortars, if any? -.

Regarding the techniques used, it should be, as well, explained the criteria for their selection and the purpose of using each of them. As there is no information about the samples (only patinas were sampled? Patinas+substrate? What is the thickness of the patina?), inerpretation of the results is not very clear for the reader. With respect to FTIR results, authors should refer to any scientific paper or database (there are many free in the website, for instance, RRUFF database accounts for FTIR and XRD results). There are some interpretations of existing minerals, but many of the peaks the author refer to in the text cannot be detected. What is the explanation for the muscovite and gypsum presence? In relation to the Optical analysis section, the quality of the images is very poor, and the assigment of some crystals to calcium oxalate has no scientific basis at all. 

In the case of SEM-EDS analysis, the samples should have been analysed not only on the surface, but also in cross-section. In this way it would have been possible to analyse the patina in its full thickness (which is unknown), its homogeneity/heterogeneity, and its relationship to the substrate, all of which can contribute to determining the origin of the patina. The scale of the microscopic images is too large, the technique is not exploited in detail; it is also not known where the EDS analyses shown in table 3 (units?) have been done (they should have been marked on the images); it is also not very scientific to assign mineralogy solely on the basis of morphology, this should always be accompanied by EDS analysis). The statement that the samples are mainly composed of C, O and Ca is not true, as a higher Si, Fe, P and Al content than Ca is observed, none of which is explained or justified.

The basalts should have been analyzed, too. It is very important to know their chemistry and mineralogy, especially the concentration and abundance of Ca-plagioclase, as the authors mention them as Ca source for combining with oxalates. 

Indispensable in this study is the use of polarizing optical microscopy for a petrographic analysis, especially of cross-sections, for determining the structure of the patina and its relationship to the substrate.

Conclusions are poor and not consistent with the results obtained.

References. Besides the indispensable mentioned Rampazzi 2019, there are some others essential for this work, such those authors working/mentioning/referring to patinas on basalts (Columbu et al. 2018, Schiavon et al. 2013, Wilson 2001, Chen et al. 2000, Edwards 1991).

I strongly encourage the authors to improve the paper.

Reply

• We thank the reviewer for his suggestions on the weak points of this paper and have tried to improve upon to the extent possible as it is the first report from of its kind from India. Mentioning precisely 349 papers on the subject reflect expertise in the field and we express our gratitude to you.
• Regarding origin of the patina, the Raigad fort is located in thick forested area of west coast and the nearest small town is around 55 km. The fort is free from air and vehicular pollution and the same is now highlighted in the manuscript. There is no industrial set up around the fort. The tourists have to use rope-way or walk through the hillock footpath to reach the fort. The rootless plants found thickly growing on the basalt stone surfaces on the entire fort complex has already been characterised for their oxalic acid secretion and as pollution indicator and referred in this manuscript. The monument has hardly been applied any chemical coating in the past. Except biological origin, any other factors were not found supporting the formation of Ca-oxalate patina. Moreover, the basaltic rock of Raigad contains around 10% of Ca-plagioclase to take part in the formation of patina. Hope this explanation may be considered by the reviewer.
• As suggested by the reviewer, the case studies have been moved to sub-head discussion and we have also tried to enlarge it. Some of the references suggested by the reviewer 1&3 have also been incorporated in the manuscript.
• Locations of the collected samples has already been shown in the manuscript Table-2. As desired by the reviewer, images showing detailed appearance of basaltic stone with patina, microbial development, protective effect of the patina and images showing deterioration of the stone from those parts where patina has been removed have now been incorporated in the manuscript. Further, sampling details like height, sampling of patina plus substrate, information about the homogeneity of the patina has now been incorporated in the manuscript and shown in colour
• To increase the content of the discussion part, some more papers recommended by reviewer1 and 3 have been incorporated and shown in colour.
• A meteogram image from the Raigad area has now been incorporated in the manuscript towards documentation of climatic conditions around the fort as desired by the reviewer - 1 and shown in colour.
• As the monument is mainly constructed (about 95%) using ashlar masonry (without any binder), wherever traces of mud/lime plaster is present, there is the formation of homogeneous patina all over the surfaces including mud/lime layer in entire complex and the same is incorporated in the manuscript in colour and also now shown in figure-2. as desired by the reviewer.
• It was not possible to sample only patina and hence patina along with substrate were sampled and studied together. The thickness of the patina is now incorporated in the manuscript.
• The basalt stone of the area has already been analysed previously. As desired the average composition of basalt stone near Raigad fort area is now incorporated in the manuscript and shown in colour.
• The FTIR results have been described as per literature survey and more references have been added for FTIR and XRD results interpretation as desired by the reviewer-1.
• In accordance to the reviewer suggestion, the optical microscopic images of the surface stone and interior substrate has now been shown and incorporated in the manuscript.
• We regret to inform that we could not perform section analysis under SEM or petrological analysis. The entire observed area under SEM were taken for EDX data and description about the major elements has already been made in the manuscript.
• No gypsum was detected in the samples and muscovite was found in the substrate during XRD, FTIR analysis and the same is shown in the data.
• Rootless plants growing in the vicinity of Raigad has already been identified by the Botanical Survey of India, a Govt. of India Institution and are characterised for their oxalic acid secretion The references are now incorporated in the manuscript for the same.
• The oxalate film has already been characterised through FTIR, XRD and SEM-EDX analysis in this paper.

 We have tried to remove the weakness of this paper to the extent possible to improve the quality of the manuscript as per reviewer suggestions. Hope the paper may be considered in its revised form. We thank the reviewers for pointing about the weak points.

Reviewer 3 Report

 

1)      About oxalate films on rocks and relevant analysis for conservation purposes the investigation the microbial deterioration of sandstone/basalts surfaces eg  from the osirion's sarcophagus chamber as affected, the various chemical and mineralogical transformations of substrate at the interface with the atmospheric agents as function of intrinsic compositional and physical characteristics of the material and also are ancient treatments on the surface of geomaterials,  analyses on the surfaces of different volcanic lithology (basalts, andesite, pyroclastic rocks), and more the authors should read and cite these as pertinent to their work:

 

Kholod K. Salama, Mona F. Ali , Said M. El Sheikh (2019) A comparison between nano calcium carbonate, natural calcium carbonate and converted calcium hydroxide for consolidation SCIENTIFIC CULTURE, Vol. 5, No. 3, (2019), pp. 35-40 DOI: 10.5281/zenodo.3340107

Stefano Columbu, Giovanni Piras, Fabio Sitzia, Stefano Pagnotta, Simona Raneri, Stefano Legnaioli, Vincenzo Palleschi, Marco Lezzerini, Marco Giamello (2018) Petrographic and mineralogical characterization of volcanic rocks and surface-depositions on romanesque monuments, Mediterranean Archaeology and Archaeometry, Vol. 18, No 5, pp. 37-64 DOI: 10.5281/zenodo.1256051.

Abeer F. Elhagrassy and Amira Hakeem (2018) Comparative study of biological cleaning and laser techniques for conservation of weathered stone in failaka island, Kuwait, SCIENTIFIC CULTURE, Vol. 4, No. 2, pp. 43-50 DOI: 10.5281/zenodo.1214561.

Abdou A.O.D. El-Derby , Maisa M.A. Mansour and Mohamed Z.M. Salem (2016) investigation the microbial deterioration of sandstone from the osirion's sarcophagus chamber as affected by rising ground water level, Mediterranean Archaeology and Archaeometry, Vol. 16, No 1, pp. 273-281 DOI: 10.5281/zenodo.46360

2)      In Fig 6 how they discriminate Calcium oxalate?

3)      The XRD in line 271 does not quote a Fig!?

 

4)      The Fig 6 does not include scales in size

Author Response

Reviewer-3

1)      About oxalate films on rocks and relevant analysis for conservation purposes the investigation the microbial deterioration of sandstone/basalts surfaces eg  from the osirion's sarcophagus chamber as affected, the various chemical and mineralogical transformations of substrate at the interface with the atmospheric agents as function of intrinsic compositional and physical characteristics of the material and also are ancient treatments on the surface of geomaterials,  analyses on the surfaces of different volcanic lithology (basalts, andesite, pyroclastic rocks), and more the authors should read and cite these as pertinent to their work:

 

Kholod K. Salama, Mona F. Ali , Said M. El Sheikh (2019) A comparison between nano calcium carbonate, natural calcium carbonate and converted calcium hydroxide for consolidation SCIENTIFIC CULTURE, Vol. 5, No. 3, (2019), pp. 35-40 DOI: 10.5281/zenodo.3340107

Stefano Columbu, Giovanni Piras, Fabio Sitzia, Stefano Pagnotta, Simona Raneri, Stefano Legnaioli, Vincenzo Palleschi, Marco Lezzerini, Marco Giamello (2018) Petrographic and mineralogical characterization of volcanic rocks and surface-depositions on romanesque monuments, Mediterranean Archaeology and Archaeometry, Vol. 18, No 5, pp. 37-64 DOI: 10.5281/zenodo.1256051.

Abeer F. Elhagrassy and Amira Hakeem (2018) Comparative study of biological cleaning and laser techniques for conservation of weathered stone in failaka island, Kuwait, SCIENTIFIC CULTURE, Vol. 4, No. 2, pp. 43-50 DOI: 10.5281/zenodo.1214561.

Abdou A.O.D. El-Derby , Maisa M.A. Mansour and Mohamed Z.M. Salem (2016) investigation the microbial deterioration of sandstone from the osirion's sarcophagus chamber as affected by rising ground water level, Mediterranean Archaeology and Archaeometry, Vol. 16, No 1, pp. 273-281 DOI: 10.5281/zenodo.46360

Reply

• The authors thank the reviewer for minutely going through the paper and suggesting necessary changes in the manuscript to enhance its scientific content. All the citations suggested by the reviewer has now been incorporated in the manuscript at different points and shown in colors both in the paper and the references.

 

2)      In Fig 6 how they discriminate Calcium oxalate?

Reply

• The calcium oxalate was identified on the basis of envelope shape (tetragonal pyramidal,3D) structure of whewellite crystal formed due to oversaturation of Ca-oxalate in longitudinal oval shape/ bio concave barbell shape and the same is now highlighted in the manuscript

 

3)      The XRD in line 271 does not quote a Fig!?

Reply

• We are sorry for the omission. Now the figure no. with description is shown in the paper in color.

 

4)      The Fig 6 does not include scales in size

Reply

• The scale has already been shown in the SEM images.

We are thankful to the reviewer for his support and pointing all the drawbacks in the manuscript. This has definitely enhanced the scientific content of the paper and we hope now the paper may be considered for publication.

Author Response File: Author Response.doc

Round 2

Reviewer 1 Report

The paper has been improved. Congratulations to the authors