Characterization of Barium Hydroxide Used as Consolidating Agent for Monumental Surfaces in Venice
Round 1
Reviewer 1 Report
The reviewer thanks the authors and editors for the opportunity to review the manuscript.
The manuscript discusses the use of barium hydroxide as a strengthening agent for natural stone. In the reviewer's opinion, this is an important and valuable article from the point of view of the protection of historic building and architectural structures. It is particularly relevant in areas with a high concentration of such buildings and existing environmental conditions that accelerate the deterioration of natural stone.
General reviewer comment: The authors should consider expanding the study. Limiting it to only two stones gives a general judgement of the effectiveness of barium hydroxide. If the authors had extended their study with more samples, this would have confirmed the conclusions set out in the manuscript.
Nevertheless, the reviewer fully accepts and recommends the article for publication.
Author Response
The authors wish to really thank the reviewer for the appreciation demonstrated to the paper. The suggestions have been fully considered and the work is going to be implemented in the next feature, using more substrates and comparing other consolidation products usually applied on stone and lithoids materials.
Reviewer 2 Report
I am very excited to read your work. It is good to see old methods being retested and revisited. i find the methodology useful to answer your questions. even if you use real samples from unknown conditions (apart from the fact e.g. that is indoor) it is good to have access and test this materials. I found areas of the text confusing. You use the word surface and substrate to mean samples. Please tidy up the text (i include some information below). I would especially advise you to make the sentences shorted and more direct easier to follow. Revisit the methodology and the results, the way that the samples are described / named confuses with regards to the results, 2 points to make. I would have liked to see clifton's published works and XRD of the crystalline material. Also, I would have loved to see the repeatability of the treatment. what you mention about the formation of barium sulphate before gypsum i find very unpredictable. your first sentence in the conclusions in my opinion needs to go.
554 - states. However, wind and rain erosion cause the gradual removal of the product from the surface and the capacity of water absorption tends to untreated values ? English? nevertheless, if this is the case the treatment may form chemically stable compounds but based on this it does not seem to be a stable conservation treatment for outdoors.
also 559 In general, the application of the treatment allows the natural degradation of the stones to be slowed down - link this statement more with your results. can you base this on 2 samples?
_______
s 30 its use is still current - change to 'although it is still used'
§35 conservative product- do you mean conservation material?
table 1 conservative- change this word everywhere to conservation. The last column in table 1 needs explanation.
also- is the cold mixture a saturated solution - need to be able to show that your comparison uses the same factors, ie that you compare the same things.
2.1 please rewrite this section in order to pay the importance to the detail of your methodology. how many samples did you have? can I follow and repeat this methodology in the way that is presented? add a table with all your samples please to make it easier to follow.
s 36 This conservative product is 35 irreversible but potentially stable over time and can tolerate further treatments based on 36 barium hydroxide as well as the application of other consolidating products years later. - this needs reference (ie evidence, or it is a hypothesis, therfore add something like ...because of the way that it works?)
2.2. Evaluation of past conservative treatments 206 - the title does not reflect the content of the section. please change and unite if necessary with the methodology
Figure 22. I am sorry but one cannot be talking about whitening seen in a digital image without providing a colour scale in the same image. please add a images that were taken with a colour scale in their frame.
s178 - good thinking
table 2, please report your± values of your measurements
s263 avoid use of word substrates- say samples instead.
s269 biodeteriogens - better to say biological activity
figure 4. very useful, please make the label for each spectrum larger
lithotype (plural lithotypes) An etched stone surface for printing, having the design in relief. A print made from such a surface. A machine, with a keyboard like that of a typewriter, for making a lithographic transfer sheet. It produces a perforated strip of paper which controls the printing.
is this what you mean when using the word lithotype?
figure 6. how did you polish the samples? sorry i might have missed this. fig. add that this is the BSE imaging
figure 8- change it in the figure- obtained at 10 keV place this before the parenthesis eg. (a)
3.2.1. why not do XRD on the crystals?
s468 discussion
s470 add to the next paragraph- make it one
s471 as strengthening agent - change to consolidant (or for consolidation treatment)
Author Response
The authours would like to thank the reviewer for careful and through reading of the manuscript and for thoughtful comments and constructive suggestions, which help to improve the quality of the manuscript.
All the suggestions have been accepted and the paper has been revised according to the reviewer’s recommendations. Comments, corrections and integrations have been assimilated in the revised manuscript.
We have responded in detail to each observations and corrections, as follows:
554 - states. However, wind and rain erosion cause the gradual removal of the product from the surface and the capacity of water absorption tends to untreated values ? English? nevertheless, if this is the case the treatment may form chemically stable compounds but based on this it does not seem to be a stable conservation treatment for outdoors.
The authors thank the reviewer for the objection. The sentence has been clarified as follows: "However, wind and rain erosion cause the gradual removal of the product from the surface and the ammount of water absorbed by the samples surfaces tends to return to untreated values."
The superficial carbonate matrix of treated samples consists mainly of barium and calcium carbonates, which was developed by carbonation and re-carbonation reactions respectively. The carbonates salts produced are comparable with natural carbonates only in chemical terms. From the minero-petrographical point of view, artificial carbonates was not subjected to slow diagenesis process and, consequently, it cannot have the same cementing properties of natural calcite. Moreover, the formed superficial layer was less compact and more porous, tending not to be comparable to the inherent carbonate matrix of the primary stone (especially in case of Carrara marble). The structure of this superficial layer may be subjected to erosion from rain and wind that progressively remove it. Even if the compounds of the superficial layer are chemically stable, its physical morphology does not allow the permaneance of the treatment layer on the samples over time.
also 559 In general, the application of the treatment allows the natural degradation of the stones to be slowed down - link this statement more with your results. can you base this on 2 samples?
The suggestion of the reviewer has been considered and the sentence has been modified as follow: "The analyses of microfragments sampled from historical Venetian monuments and specimens allowed to confirme the results obtained from experimental samples. Moreover, they demonstrated that the application of the treatment allows the natural degradation of the stones to be slowed down, preserving the possibility of the re-treatment of the surface and ensuring a better conservation over time."
_______
s 30 its use is still current - change to 'although it is still used'
The sentence has been rephrased as suggested by the reviewer.
s 35 conservative product- do you mean conservation material?
"Conservative" term has been replaced with "conservation" everywhere in the paper, as kindly requested by the reviewer.
table 1 conservative- change this word everywhere to conservation. The last column in table 1 needs explanation.
The title of the last column of table 1 has been renamed "conservation condition". The content of this column describes the environment and the time of exposure for each treated object.
also- is the cold mixture a saturated solution - need to be able to show that your comparison uses the same factors, ie that you compare the same things.
The cold mixture of barium hydroxide, urea and glycerine was prepared following the recipe describe in introduction paragraph (lines 56-58).
2.1 please rewrite this section in order to pay the importance to the detail of your methodology. how many samples did you have? can I follow and repeat this methodology in the way that is presented? add a table with all your samples please to make it easier to follow.
Following the reviewer suggestions, the authors added the number of considered samples in table 1. In this way, reading the information in the table and the explanation of experimental procedure as described in paragraph 2.1, the authors consider now the methodology easier repeatable.
s 36 This conservative product is 35 irreversible but potentially stable over time and can tolerate further treatments based on 36 barium hydroxide as well as the application of other consolidating products years later. - this needs reference (ie evidence, or it is a hypothesis, therfore add something like ...because of the way that it works?)
The reference has been added in the text.
2.2. Evaluation of past conservative treatments 206 - the title does not reflect the content of the section. please change and unite if necessary with the methodology
According to the reviewer suggestion, the title of paragraph 2.2 has been rewritten in “Monitoring procedure for evaluating past conservative treatments”.
Figure 22. I am sorry but one cannot be talking about whitening seen in a digital image without providing a colour scale in the same image. please add a images that were taken with a colour scale in their frame.
The authors have produced a new figure in which color chart is present for better appreciating whitening effect, as proposed by the reviewer.
s178 - good thinking
The authors are sorry but thy cannot understand to what the revision is referred.
table 2, please report your± values of your measurements
The authors agree with the reviewer that deviation standards values in table 2 may confirm the goodness of data. However adding these values the table resulted unreadable because of space. For this reason, they prefer to remove from the table ΔL, Δa and Δb values.
s263 avoid use of word substrates- say samples instead.
The word “substrates” has been replaced using “samples”
s269 biodeteriogens - better to say biological activity
The authors has accepted the suggestion of the reviewer
figure 4. very useful, please make the label for each spectrum larger
Accepting the reviewer’s suggestion, the figure has been revised.
lithotype (plural lithotypes) An etched stone surface for printing, having the design in relief. A print made from such a surface. A machine, with a keyboard like that of a typewriter, for making a lithographic transfer sheet. It produces a perforated strip of paper which controls the printing.
is this what you mean when using the word lithotype?
Lithotype is the correct term currently use in minero-petrographycal field for defining a rock. As reported in mindat.org:
Lithotype: A rock defined on the basis of certain selected physical characters.
figure 6. how did you polish the samples? sorry i might have missed this. fig. add that this is the BSE imaging
The term “cross-section” reported in the caption of figure 6 means a specific preparation of the sample very common in this field. The microfragment is embeeded in a epoxy resin, then perpendicularly cutted, abraded and polished using grinding discs.
The specification requested has been added.
figure 8- change it in the figure- obtained at 10 keV place this before the parenthesis eg. (a)
The authors are sorry but thy cannot understand what the reviewer means.
3.2.1. why not do XRD on the crystals?
The crystals were analysed by XRD. Those crystallized on a slide resulted in baryte, whereas the analysis of powder from the treated samples showed the presence of both calcite and baryte.
The results were not included into the paper because they do not give relevant additional information to the paper.
s468 discussion
According with the reviewer, the title of the paragraph has been corrected.
s470 add to the next paragraph- make it one
Since the other reviewers did not give any suggestion about it, the authors prefer to maintain Discussion and Conclusion paragraphs separated.
s471 as strengthening agent - change to consolidant (or for consolidation treatment)
The authors thank the reviewer and the term has been replaced.
Author Response File: 
Author Response.docx
Reviewer 3 Report
Generally:
The title contains the word "strengthening", however, the paper does not discuss strengthening - I recommend to replace this word with "consolidating" not to confuse the reader.
reference concerning measurements of strengthening effect of barium hydroxide can be completed with: Slížková, Z., Drdácký, M., Viani, A.: Consolidation of weak lime mortars by means of saturated solution of calcium hydroxide or barium hydroxide. Journal of Cultural Heritage. 2015, 16 (4), (July-August). pp. 452-460. ISSN 1296-2074
Figure 1: "red circles" not visible - would it be possible to replace by whit circles
Line 121: is it possible to identify the amount of the penetrated agent?
Line 404 and 462: font size needs correction
Author Response
The authors wish to thank the reviewer for the kind suggestions that allowed to increase the quality of the paper. Every tip has been considered as follows.
1) The title contains the word "strengthening", however, the paper does not discuss strengthening - I recommend to replace this word with "consolidating" not to confuse the reader.
The authors welcome the reviewer’s suggestion and replace in the title the word “strengthening” with “consolidating”.
2) reference concerning measurements of strengthening effect of barium hydroxide can be completed with: Slížková, Z., Drdácký, M., Viani, A.: Consolidation of weak lime mortars by means of saturated solution of calcium hydroxide or barium hydroxide. Journal of Cultural Heritage. 2015, 16 (4), (July-August). pp. 452-460. ISSN 1296-2074
The proposed reference has been verified and added in the text.
3) Figure 1: "red circles" not visible - would it be possible to replace by whit circles
The authors agree with reviewer’s kind advice and in figure 1 all the red cycles have been replaced with white ones.
4) Line 121: is it possible to identify the amount of the penetrated agent?
The information requested by the reviewer was expressed in line 119: “the dry uptake observed in Carrara marble and Vicenza white limestone samples was dissimilar, in particular 0,03 g and 2,60 g respectively.”
4) Line 404 and 462: font size needs correction
The font size has been controlled and adapted to the style of the previous text.
Round 2
Reviewer 2 Report
s9 and 10. delete the first sentence and edit the second like: Barium hydroxide has been one of the most widely used materials for the consolidation of calcareous stones during the 19th and 20th centuries. Consolidation using this material is achieved by a carbonation reaction.
s13. EDIT. delete THE before the word results. the second part of the sentence does not make sense. Could re-write as : after ; results are often in conflict and more experimental work using modern analytical techniques is necessary to shed light on the mechanisms involved in the effectiveness of the method. S15This research aims to...
S17 delete SOME can replace by a small number of
S21 for future conservation
S21 delete and the synthesis of innovative compounds or explain what these are for. do you mean crystallographic data of new synthesised crystals, or new materials for conservation. ? - this is not clear
S46 replace having with with
S47-49 i understand what you try to say, but plz write shorter sentences to avoid misunderstandings. Long sentenses make this hard to follow.
S61 somebody- rephrase this like the effectiveness of the treatment was questioned___or just say who did this
S85, please add at the end of the sentence: over time on a series of selected objects treated in the past. [this helps with understanding better the methodology] ALSO ADD REFERENCE TO TABLE , It would be better to see one table for the experimental sample (laboratory samples) and the methods that were treated, and another for the real past conservation treatments/.
S86. For this purpose- delete
S136 etc plz change paragraph for each method that you used.
S162, how did you overcome problems with beam damage at 25KeV? earlier in the text S79 you menation that this is a problem with SEM-EDS S69
S210 do excuse me, but what is the solution and method of application? is the information in table 1 and just below this? plz change table 1 more to show all details of your samples. add numbers to each sample sample 1, etc to show how many samples you analysed
S303, I would have liked to see here XRD anaslyses and not SEM-EDX. in fact, the edx here does not add much information, especially when thinking that you mentioned the limitations of the method earlier. Please exclude the edx data, the ftir should be enough for the purpose of chemical analyses. It is a pitty you have not used the ftir microscope in reflectance mode. it would have been very interesting to map the distribution of the cxrystall composition across the sample (inward penetration, check the formation of a skin etc)
S356, ok, this is fine. good use of the sem-edx spectra here. i note that the spectra were not taken at the same time as the images. The images were taken at 20kv careful, plz explain this in the figure as you explain it in the txt.
S411 plz do not make one single sentence paragraphs.
S412 and S413 change to: satisfies several conservation choice criteria.
S413 the curring process occurs - change to: consolidation takes place
S415 - confusing. do you mean, the chemical nature of which ensures chemical compatibility with the carbonate substrate object.
S416 - change to: The presence of Ba in the crystals, permits its mapping with SEM-EDX in cross-sections to identify the penetration and assess the treatment.
S422 sorry i do not understand this. if it is not important just delete it till the end of the paragraph.
S425 - ok, but have you compared the method of application? PLZ MAKE SURE YOU COMPARE SIMILAR METHODS
s426, this is important for conservation. plz explain which solution gave better penetration? the one with the glycerine?
S430 YOU OMMIT IMPORTANT EXPERIMENTAL INFORMATION. plz make sure that the reader would be able to follow your methodology and if one repeats your work can come to the same findings. how long for was the impregnation? which solution do you refer o? which sample?
was the same person who brushed the samples? did they use the same asize brush?
S440, soldering is not the correct use of word here
S443 too much wetting of the surface can make the surface very heavy and if it it too fragile, it may fall. it appears that one can experience this when consolidating plaster. how did you overcome this problem?
S445, ok but what does the inner part of the sample mean? what is the depth of penetration??
S448 Wind and water erosion
S448 this s4entence does not add to your argument-delete. reduce the thickness of the superficial layer during weathering, as ascertained by microscopic observations and 449 by monitoring the capacity of treated stone to absorb water. In fact,
477-delete
483 confirm-TYPO
Author Response
The authors thank the reviewer for the suggestions.
The revisions have been taken into consideration by the authors, improving the quality of the paper, as follows in detail:
s9 and 10. delete the first sentence and edit the second like: Barium hydroxide has been one of the most widely used materials for the consolidation of calcareous stones during the 19th and 20th centuries. Consolidation using this material is achieved by a carbonation reaction.
The authors deleted the first sentence as suggested and changed the phrase as follows:
“Barium hydroxide has been one of the most widely used inorganic materials for the consolidation of calcareous stones during the 19th and 20th. The consolidation process occurs by a carbonation reaction.”
s13. EDIT. delete THE before the word results. the second part of the sentence does not make sense. Could re-write as : after ; results are often in conflict and more experimental work using modern analytical techniques is necessary to shed light on the mechanisms involved in the effectiveness of the method. S15This research aims to...
The authors rephrased the sentence as follows:
“Several researchers studied the consolidation mechanism; however, the results are sometimes in conflict and more experimental work using modern analytical techniques and a multi-analytical approach is necessary to shed light on the mechanisms involved. This research aims to …”
S17 delete SOME can replace by a small number of
The authors replaced “some” with “few”.
S21 for future conservation
Since the consolidation procedure is part of a restoration intervention, the author did not change the word used.
S21 delete and the synthesis of innovative compounds or explain what these are for. do you mean crystallographic data of new synthesised crystals, or new materials for conservation. ? - this is not clear
The sentence has been clarified as follows:
“The results prompted a number of considerations useful for future restorations and for developing innovative compounds for consolidation interventions.”
S46 replace having with with
The word “having” is preferred here because it allows to better specify the characteristics of the multi-layered solid solution of barium-calcium carbonate
S47-49 i understand what you try to say, but plz write shorter sentences to avoid misunderstandings. Long sentenses make this hard to follow.
The sentence has been rephrased as follows:
In the outer layers of the crystalline structure calcium ions are partially replaced by barium ions. For this reason, the calcium content would be high in the adjacent areas to calcite minerals, decreasing as the distance from them increases.
When the distance between calcite grains is significant, the amount of pure barium carbonate in the pores of the stone is greater”
S61 somebody- rephrase this like the effectiveness of the treatment was questioned___or just say who did this
The sentence has been changed as follows:
“Even though the effectiveness of the treatment was questioned, especially when applied by capillary absorption in situ,…”
S85, please add at the end of the sentence: over time on a series of selected objects treated in the past. [this helps with understanding better the methodology] ALSO ADD REFERENCE TO TABLE , It would be better to see one table for the experimental sample (laboratory samples) and the methods that were treated, and another for the real past conservation treatments/.
The authors prefer not to include “over time on a series of selected objects treated in the past” since also the weathering and artificial ageing used in case of experimental laboratory samples allowed the evaluation of the conservation treatment stability and effectiveness.
The reference to table has been added.
S86. For this purpose- delete
The suggestion has been accepted.
S136 etc plz change paragraph for each method that you used.
The suggestion has been accepted.
S162, how did you overcome problems with beam damage at 25KeV? earlier in the text S79 you menation that this is a problem with SEM-EDS S69
The method used provided an accelerating voltage from 25 to 10 KeV, not equal to 25 KeV. This value was useful to evaluate the limits of the experimentation.
S210 do excuse me, but what is the solution and method of application? is the information in table 1 and just below this? plz change table 1 more to show all details of your samples. add numbers to each sample sample 1, etc to show how many samples you analysed
The reader can find all the information related to the solution and method of application in paragraph 2.1 of chapter 2, Materials and Methods. In table 1, this information is summarized and the number of the specimens specified.
S303, I would have liked to see here XRD anaslyses and not SEM-EDX. in fact, the edx here does not add much information, especially when thinking that you mentioned the limitations of the method earlier. Please exclude the edx data, the ftir should be enough for the purpose of chemical analyses. It is a pitty you have not used the ftir microscope in reflectance mode. it would have been very interesting to map the distribution of the cxrystall composition across the sample (inward penetration, check the formation of a skin etc)
As explained in the previous response to reviewer, XRD analyses were performed on treated specimens without giving useful information for the aim of the research. Peaks of baryte and calcite were observed, as already detected by FTIR measurements. FTIR gave more information than XRD regarding not only the composition of the treated stones but also the alteration mechanism during time. For this reason, it was preferred to show FTIR spectra. The use of µFTIR on cross-sectioned samples implied the cutting of the specimens during the monitoring procedure. In this way the dimensions of the specimens would be necessary decreased over time. The distribution of the crystals, their composition, the penetration depth, and the formation of a superficial layer, as requested by the reviewer, were investigated by SEM-EDS analyses (figure 6). This analytical technique also confirmed the morphological aspect of the developed secondary products in the form of acicular crystals, having various grain sizes.
Moreover, the use of SEM-EDS was relevant in order to demonstrate the interpretation issue revealed in case of references 14, 20 and 21.
S356, ok, this is fine. good use of the sem-edx spectra here. i note that the spectra were not taken at the same time as the images. The images were taken at 20kv careful, plz explain this in the figure as you explain it in the txt.
The reviewer is right, SEM images were captured using 20 KeV, as reported in the figures a) and b), whereas EDX analyses were performed with 10 KeV, as described in the caption.
S411 plz do not make one single sentence paragraphs.
The first sentence is not a paragraph but the opening phrase of chapter 4.
S412 and S413 change to: satisfies several conservation choice criteria.
The reviewer’s request has been accepted.
S413 the curring process occurs - change to: consolidation takes place
The suggestion has been accepted.
S415 - confusing. do you mean, the chemical nature of which ensures chemical compatibility with the carbonate substrate object.
The sentence has been clarified as follows:
“The chemical nature of the restoration product (BaCO3), ascertained by FTIR and EDX, guarantees the good chemical compatibility with a calcium carbonate substrate (barium is vicarious of calcium).”
S416 - change to: The presence of Ba in the crystals, permits its mapping with SEM-EDX in cross-sections to identify the penetration and assess the treatment.
The suggested change varies the meaning of the concept. The authors decided to maintain the previous version of the sentence.
S422 sorry i do not understand this. if it is not important just delete it till the end of the paragraph.
The sentence has been clarified as follows:
The measured amount of calcium was higher in the analysed areas next to calcite crystals, because of a higher matrix effect, and it decreased as the distance from them increased.
S425 - ok, but have you compared the method of application? PLZ MAKE SURE YOU COMPARE SIMILAR METHODS
The application methods were comparable.
s426, this is important for conservation. plz explain which solution gave better penetration? the one with the glycerine?
A sentence was added in this regard:
“The solution based on barium hydroxide, glycerine and urea guaranteed a good distribution and penetration into Lumachella del Tasso substrate. In contrast, no trace of the treatment was observed in case of Carrara marble, which have a lower porosity, using both pure barium hydroxide solution and mixture of barium hydroxide, urea, and glycerine.”
S430 YOU OMMIT IMPORTANT EXPERIMENTAL INFORMATION. plz make sure that the reader would be able to follow your methodology and if one repeats your work can come to the same findings. how long for was the impregnation? which solution do you refer o? which sample?
The information related to solutions, application methods and experimental methods is described in Chapter 2.
was the same person who brushed the samples? did they use the same asize brush?
Yes, it was.
S440, soldering is not the correct use of word here
“colmatating” replaced now “soldering”
S443 too much wetting of the surface can make the surface very heavy and if it it too fragile, it may fall. it appears that one can experience this when consolidating plaster. how did you overcome this problem?
The authors are sorry but the aims of the paper is the consolidation of stone materials. No experimentation were done on plaster substrates by the authors. However, the reviewer’s suggestion will be taken into consideration for future works.
S445, ok but what does the inner part of the sample mean? what is the depth of penetration??
As explained at S425, the penetration depth depends on the porosity and state of conservation of the stone. Generally speaking, “the inner part” represents the layer of maximum penetration depth of the treatment solution in a substrate.
S448 Wind and water erosion
The authors are sorry but cannot understand the reviewer’s objection.
S448 this s4entence does not add to your argument-delete. reduce the thickness of the superficial layer during weathering, as ascertained by microscopic observations and 449 by monitoring the capacity of treated stone to absorb water. In fact,
The suggestion has been accepted.
477-delete
The authors disagree with the reviewer’s suggestion.
483 confirm-TYPO
The authors thank the reviewer for the revision.
