A Study and Comparative Analysis of the Action of the Deacidifying Products Bookkeeper® and Nanorestore Paper® on Plant Textile Fibres
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsSee attached file
Comments for author File: 
Comments.pdf
Author Response
Reviewer 1
Revision of manuscript “Study and comparative analysis of the action of the deacidifying products Bookkeeper® and Nanorestore Paper® on plant textile fibers”
The authors present an interesting work where commercial formulations, Nanorestore Paper® and Bookkeeper®, normally used as deacidifying products for paper, are tested on cotton, linen, and jute canvas mock-ups as protecting deacidifying agents. Although designed for paper, these commercial products have been used often by conservators on other cellulose-based artifacts, with no particular attention about the potential risks for the objects. This study has the merit to evaluate the actual impact of these products on cellulose-based textiles of very common use in art, like canvas, which could benefit from the applications of deacidifying agents. To this purpose, the mock-ups were artificially degraded, treated with the various formulations, and then artificially aged at high temperature and relative humidity (60°C, 90%) for many days to test the efficiency of the treatments in terms of pH, discolorations, morphology. The study shows that unwanted effects, like very high local pH, formation of deposits, discoloration, can occur when these products are used for applications on items different than the ones these products were designed for. I’ve particularly appreciated the care the authors used in evaluating not only the chemical effects, but also the visual effects (deposits, discolorations). However, before publications, some issues need to be properly addressed (see major and minor revisions).
The authors thank reviewer_1 for having understood the purpose of this work. In the following pages, they will respond in detail to all the comments, aiming to clarify and better explain in the text the experimental work carried out.
Major revisions: -
Comment 1: The authors seem to be more favorable to the use of Bookkeeper for cellulose-based canvas, due to the milder effect on pH. However, Bookkeeper, at least in the formulation used by the authors, poses series health issues, since perfluoroalkanes, used in this product as solvents, are recognized as persistent chemical pollutants, with long biological permanence in the tissues. Even very small amounts of them can be a main concern (e.g., for PFOA even amount of 20 ppb are considered a potential risk) and actually ECHA is evaluating to remove perfluoroalkyl substances (https://echa.europa.eu/-/five-european-states-call-for evidence-on-broad-pfas-restriction). Therefore, the authors should at least say something about this point, since the Bookkeeper in the formulation used by the authors is not likely to be usable in the future.
Response 1: The authors do not express any value judgment regarding the choice of one product over another, nor do they intend to make any assessment about the potential future use of the tested products. In this respect, there is no intention to promote the use of Bookkeeper over Nanorestore products. The selection of the products was based solely on their widespread use in restoration practice. The aim of this work was therefore to evaluate their effects on textile fibres within an operational restoration context.
Comment 2: In Table 2, the authors state that NP3P, NP3S and NE3S applications result in pH higher than 9 on cotton and linen, but in the figures 1 and 2 the pH values at “0” days are below 8, which is a very good value for cellulose. The authors should explain this discrepancy.
Response 2: The values reported in Table 2, referring to the application of the various products in their different formulations, correspond to the moment immediately after application (time 0). In Figures 2, however, the first measurement shown represents the pH value recorded after 1 day of artificial degradation. The graph is based on pH measurements taken on days 1, 4, 11, 26, 57, and 128.
Time 0 was deliberately excluded from the graph for reasons of clarity: including it would have compressed the data along the y-axis and rendered it visually indistinguishable from time 1 on the x-axis.
The rapid increase in pH was observed immediately after application; although the value stabilised after just one day, the authors consider this information to be relevant, since in real-life applications, the risk of damaging the structural and pictorial materials, due to the possible penetration of the products, must be carefully considered.
However, in response to the valuable comments received, Figures 2, 3, and 4 have been revised to improve clarity and completeness. Specifically, the pH value corresponding to time zero, which was previously omitted for graphical reasons, has now been included. Additionally, a logarithmic scale has been applied to the x-axis in order to better represent the early stages of the ageing process and to enhance the readability of the data distribution over time.
Comment 3: Lines 86-94: The protocol used is not well described. 1) The method proposed by Nechyporchuk, and used on the mock-ups, is not just an “acidification”, is an artificial ageing/degradation method for cotton canvas, combining oxidation and hydrolysis (actually, both H2O2 and H2SO4 are used, with H2O2 being an oxidant and H2SO4 the acidifying substance). The authors should specify this point. Since after this protocol the authors use a thermal and high RH ageing, I propose to re-define “artificial degradation” the protocol, when in the article it is referred to it.
Response 3: The authors have chosen this protocol because, according to the literature, it presents the most aggressive action and is commonly selected as it ensures the production of stably acidified substrates, thus ready for the deacidification protocol. However, the observation is absolutely acceptable, as it is indeed a combined acidifying and oxidising action. Therefore, in the text, the protocol has been changed and is now referred to as “artificial degradation.”
Comment 4: The authors state that “the mock-ups were divided..[] and soaked in a solution of…for a total of 72 hours” (Lines 91-92). I suppose that this is still part of the original Nechyporchuk protocol (by the way, it is written “H2O” instead of “H2O2”), and I suppose that the mixture with this proportion of hydrogen peroxide and sulphuric acid was the right one to have pH=4. So, the authors should explain better, something like:”The correct percentage of H2O2 and H2SO4 for getting a pH=4 in the specimens was a mixture of 330 mL of…and .. The mock-ups were divided etc.”
Response 4: O. Nechyporchuk's protocol specifies two different mixtures. In order to identify the most suitable formulation for the specific case, tests were carried out taking both into consideration: 1 ml of Hâ‚‚SOâ‚„ in 200 ml of Hâ‚‚Oâ‚‚ and 10 ml of Hâ‚‚SOâ‚„ in 200 ml of Hâ‚‚Oâ‚‚ . These were tested on a total of 4 samples, two of linen and two of cotton, in order to assess the degree of acidification achieved. The samples were left immersed in their respective solutions for a total of 72 consecutive hours, after which they were rinsed by immersing them in deionised water for 5 minutes, repeating the operation twice. Once the acid residues had been removed, the fabrics were left to dry in an oven at a temperature of 40°C for a total of 48 hours. At each step of the process, the respective surface pH values were measured in order to calibrate the rinsing times and to compare their trends in relation to the final values measured after drying. Based on the results of the final measurements of the different fabrics, it emerged that, in relation to the operating methodology used, the moderately acidic solution (1 ml of Hâ‚‚SOâ‚„ in 200 ml of Hâ‚‚Oâ‚‚ ) was sufficient, which, in addition to ensuring the achievement of a pH value suitable for the specific case, it allowed the use of a smaller quantity of sulphuric acid and therefore a lower risk for the operator.
In agreement with the reviewer, the explanation and justification of the protocol have been expanded in the Materials and Methods section.
The typo "Hâ‚‚O" instead of "Hâ‚‚Oâ‚‚" has been corrected.
Comment 5: Lines 129-130: “The specimens…in a ventilated oven at a constant temperature of 60°C and in a room temperature chamber with a relative humidity of 90%”. This is not clear to me: were the samples placed before in a ventilated oven at 60°C and then in a chamber at room temperature? In this case, what was the RH of the oven? How long the time in the oven? How long in the chamber? Or were the samples placed inside a chamber with RH 90%, and the chamber was inside a ventilated oven at 60°C? The authors must make clear this point, describing better the artificial ageing procedure.
Response 5: The authors have added a sentence to better clarify the type of treatment. The ageing process involved placing the samples for half of the time between each measurement in a humidification chamber at room temperature, and for the other half in a ventilated oven at 60 °C. From an operational standpoint, the total treatment time was calculated.
This approach was chosen in order to observe and objectively assess the behavior of the deacidifying agents in a context simulating environmental variation, characterized by temperature peaks (associated with low humidity) and humidity peaks (at low temperature).
Comment 6: Minor revisions: Lines 36: “e.g., air pollutants” (add a comma after e.g.). Lines 84-85: what does it mean “canvas with minimal reinforcement (1:1)”? Is maybe (1:1) referred to the weave? In this case, the sentence should be better reformulated.
Response 6: The expression “unbleached fabrics with minimal reinforcement (1:1) and not subjected to any treatment” (lines 84–85) refers to the type of weave of the selected fabrics, namely one weft thread for each warp thread (ratio 1:1).
General comment After this study, I would not recommend either Bookkeeper or NanorestorePaper for the use on canvas. However, while Bookkeeper is not going to be used longer in this formulation in the future, a different formulation of Nanorestore could be designed to be used specifically on canvas.
Author Response File: 
Author Response.docx
Reviewer 2 Report
Comments and Suggestions for AuthorsDeacidifying of textiles heritage is an important task for its longtime conservation. This research aims to evaluate the effectiveness of deacidifying treatments for the restoration of textiles used as supports for works of art using two commercial products: magnesium oxide from Bookkeeper™ and calcium hydroxide from Nanorestore™. The authors compare their advantages and disadvantages and provide suggestions, which is very important for specific application. However, before publication, the following issues should be addressed.
- The authors claim that they performed SEM test, which is illustrated in Figure 7. Nevertheless, there is no Figure 7 in the draft. They must provide Figure 7 and reasonably explain why the SEM images are missing.
- I think that Figure 4 and Figure 5 can be combined as one.
- Why is the artificial ageing time arranged as 1, 4, 11, 26, 57 and 128 days? From 57 to 128 days, the time span is too long.
- In my opinion, the authors need compare the prices of Bookkeeper™ and Nanorestore™ to comprehensively understand the advantages and disadvantages of them.
- Why is the brush application methodology in Bookkeeper™ absent?
- I think that Figure 4-Figure 6 should be included error bar. They made numerous experiments.
- The quantity of references included is insufficient. It is recommended that the number of references should be 25 or more. Additionally, there are numerous researches on nanolime that have been conducted. I think that the following reference needs to be considered.
Nano Ca(OH)2: A review on synthesis, properties and applications. J. Cult. Herit. 50:25-42.
Author Response
Reviewer 2
Deacidifying of textiles heritage is an important task for its longtime conservation. This research aims to evaluate the effectiveness of deacidifying treatments for the restoration of textiles used as supports for works of art using two commercial products: magnesium oxide from Bookkeeper™ and calcium hydroxide from Nanorestore™. The authors compare their advantages and disadvantages and provide suggestions, which is very important for specific application. However, before publication, the following issues should be addressed.
Comment 1: The authors claim that they performed SEM test, which is illustrated in Figure 7. Nevertheless, there is no Figure 7 in the draft. They must provide Figure 7 and reasonably explain why the SEM images are missing.
Response 1: The authors apologize for the inconvenience; the issue was likely due to a problem during the image upload process. All high-resolution images are, in any case, available in the supplementary materials. The authors have reinserted Figure 7 in the text.
Comment 2: I think that Figure 4 and Figure 5 can be combined as one.
Response 2: The authors’ decision to present them separately is motivated by the demonstrated reduction in quality when using a single combined image.
Comment 3: Why is the artificial ageing time arranged as 1, 4, 11, 26, 57 and 128 days? From 57 to 128 days, the time span is too long.
Response 3: We thank the reviewer for the observation. We adopted a monitoring method based on a pseudo-exponential trend, which is commonly used in the field of chemistry to highlight both rapid variations (in the initial part of the curve) and slower changes (in the final part). This approach was chosen in order to better capture the dynamics of the ageing process over time. A clarifying sentence has been added in the Materials and Methods section.
Comment 4: In my opinion, the authors need compare the prices of Bookkeeper™ and Nanorestore™ to comprehensively understand the advantages and disadvantages of them.
Response 4: The authors do not intend to frame this as an economic issue, as it is considered secondary—especially given that the amounts involved are not substantial—and because prices vary significantly from country to country and from supplier to supplier. However, if such a comparison cannot be avoided: a 150 g spray can of Bookkeeper costs €77 on the CTS website, while Nanorestore is priced between €98 and €122 per liter, depending on the formulation (with propanol-based versions being more expensive).
The authors wish to emphasize that the purpose of this work, as clearly stated in the manuscript, is not commercial but purely scientific. The analytical observation of the behavior of two deacidifying products commonly used in the field of restoration is aimed solely at objectively describing their behavior in operando.
Comment 5: Why is the brush application methodology in Bookkeeper™ absent?
Response 5: The brush application for Bookkeeper has not been tested because the aim of the work is to test the application methods that a painting restorer may realistically encounter in the laboratory. To this end, the application methods tested were those indicated by the manufacturer in the technical data sheet: unlike Nanorestore products, the Bookkeeper product does not indicate the possibility of applying the product with a brush.
Comment 6: I think that Figure 4-Figure 6 should be included error bar. They made numerous experiments.
Response 6: The error bars are included in the graphs but are not visible because they are covered by the markers. The average error observed ranges between 0.01 and 0.015 pH units.
Comment 7: The quantity of references included is insufficient. It is recommended that the number of references should be 25 or more. Additionally, there are numerous researches on nanolime that have been conducted. I think that the following reference needs to be considered.
Response 7: As suggested by the reviewer, some publications have been added to the article, although the authors believe that citations should serve the work, and not the other way around.
Nano Ca(OH)2: A review on synthesis, properties and applications. J. Cult. Herit. 50:25-42.
Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for AuthorsThe paper "Study and comparative analysis of the action of the deacidifying products Bookkeeper® and Nanorestore Paper® on plant textile fibres" by Amalia Nani, Chiara Ricci, Alessandro Gatti, and Agostino Angelo could be an interesting study aimed to compare two different methodologies for deacidifying purposes in the field of textiles used as supports for works of art. Indeed, I believe that in the present form it cannot be accepted for publication due to the strong major criticities as below illustrated.
Without specifying what was the exact amount in mg/cm2 of the nanoparticles applied onto the mock-ups it is impossibile to discuss the changes in pH, colorimetric propreties, and SEM morphologies, as already well exposed in ref. 16.
Due to the fact that the spray/brush application procedures cannot be considered - without the above mentioned amount of nanoparticles deposed - identical for all the specimens, it is obvious that changes in pH, colorimetric and SEM morphological properties clearly cannot be explained in terms of MgO or Ca(OH)2 particles concentration effect. Indeed, the confirmation of this is the anomalous -positive - result of NE3P with respect to the three other Nanorestore treatments. The Authors do not try to explain why the same product (Ca(OH)2 nanoparticles) succeeds in keeping quite low the pH with respect to the other three treatments: brush cannot be the reason (NP3P at the same concentration with 2-propanol by brush gave pH > 9); the solvent cannot be the cause, since it is simply the dispersant medium not acting as active for changing the pH; moreover, ethanol is more hygroscopic than 2-propanol and therefore NP3P should be gentler than NE3P and the results shows the opposite! The only explanation could be that in the case of NE3P the Authors applied by brush a smaller amount in mg/cm2 of the alkaline naoparticles. But this could be confirmed only repeating the experiments changing for each application the amount in mg/cm2 of the applied nanoparticles.
I find an inconsistency between Table 2 and Figs. 1-3: The values reported in Table 2 after the application of the products I suppose are at time = 0 with respect to the successive artificial ageing cycles but the values at time = 0 in Figs. 1-3 do not exceed pH =9!
Lines 128-131: "The specimens were subjected to an artificial ageing cycle in a ventilated oven at a constant temperature of 60°C and in a room temperature chamber with a relative humidity of 90%" . Two different steps? But then in Figs 1-3 the Authors report the check of the pH throughout the artificial ageing process: what process ventilated oven or room temperature chamber?
Figs. 8 and 9 are not reported at least in the version I received.
Due to the above described criticities I suggest the Authors to made new experiments, re-write the paper, and submit again a new paper to solve the strong weaknesses of the paper in the present form.
Author Response
Reviewer 3
The paper "Study and comparative analysis of the action of the deacidifying products Bookkeeper® and Nanorestore Paper® on plant textile fibres" by Amalia Nani, Chiara Ricci, Alessandro Gatti, and Agostino Angelo could be an interesting study aimed to compare two different methodologies for deacidifying purposes in the field of textiles used as supports for works of art. Indeed, I believe that in the present form it cannot be accepted for publication due to the strong major criticities as below illustrated.
Comment 1: Without specifying what was the exact amount in mg/cm2 of the nanoparticles applied onto the mock-ups it is impossible to discuss the changes in pH, colorimetric properties, and SEM morphologies, as already well exposed in ref. 16.
Due to the fact that the spray/brush application procedures cannot be considered - without the above mentioned amount of nanoparticles deposed - identical for all the specimens, it is obvious that changes in pH, colorimetric and SEM morphological properties clearly cannot be explained in terms of MgO or Ca(OH)2 particles concentration effect. Indeed, the confirmation of this is the anomalous -positive - result of NE3P with respect to the three other Nanorestore treatments.
Response 1: The authors respectfully disagree with the statement made by reviewer 3.
Indeed, the concentration of all the applied products is correctly reported in the Materials and Methods section. By definition, the concentration of a solution expresses the ratio between the amount of solute and the amount of solvent; it is therefore an intensive property, constant at every point in the solution, regardless of the volume taken. Since pH also represents a measure of the concentration of hydrogen ions in solution, all the measured data are fully representative.
The evaluation of surface coverage in mg/cm² is simply an expression of the concentration on a thin layer and is linearly correlated to the initial concentration of the solution. Moreover, the authors never claimed that the quantities applied were identical, precisely because different application methods were used. This choice was intentional and motivated by the desire to simulate an in operando condition, that is, an application carried out by a conservator according to the operational guidelines provided by the manufacturers of the tested products.
Naturally, all applications were carried out by the same conservator, aiming to ensure the highest possible level of repeatability.
Comment 2: The Authors do not try to explain why the same product (Ca(OH)2 nanoparticles) succeeds in keeping quite low the pH with respect to the other three treatments: brush cannot be the reason (NP3P at the same concentration with 2-propanol by brush gave pH > 9); the solvent cannot be the cause, since it is simply the dispersant medium not acting as active for changing the pH; moreover, ethanol is more hygroscopic than 2-propanol and therefore NP3P should be gentler than NE3P and the results shows the opposite! The only explanation could be that in the case of NE3P the Authors applied by brush a smaller amount in mg/cm2 of the alkaline naoparticles. But this could be confirmed only repeating the experiments changing for each application the amount in mg/cm2 of the applied nanoparticles.
Response 2: The aim of this study was to evaluate the action of certain products commonly used in the field of restoration, adopting an application method as realistic as possible. To this end, both brush and spray applications were carried out by a restorer, with particular attention paid to maintaining the greatest possible consistency in terms of quantity and quality, according to the instructions provided by the manufacturers.
Considering that, in practical situations, these products are applied directly by a restorer, it is not possible to completely rule out some variability in the application. However, it is important to highlight that, in certain cases involving works particularly sensitive to alkaline environments, this variability may represent a potential risk (as in the case, for example, of azurite-based paint layers, which degrade rapidly in basic pH environments and could therefore be damaged by the penetration of the products, even if applied on the reverse side of the support).
The aim of this work is therefore to evaluate realistic application methods for restorers, in order to offer an objective, albeit modest, contribution to raising awareness on these aspects, helping to inform more conscious choices during restoration interventions.
Regarding the anomalous, and positive, result observed for the NE3P treatment compared to the other three Nanorestore Paper® treatments, the authors attributed it to the higher volatility of ethanol, which altered the rheological properties of the suspension on the brush, thereby reducing the amount of product transferred to the textile support. As previously mentioned, these aspects are inherent to the application method for which these products were designed and inevitably reflect a certain degree of subjectivity, although controlled, inherent in manual application by the restorer.
Comment 3: I find an inconsistency between Table 2 and Figs. 1-3: The values reported in Table 2 after the application of the products I suppose are at time = 0 with respect to the successive artificial ageing cycles but the values at time = 0 in Figs. 1-3 do not exceed pH =9!
Response 3: The data reported in Table 2 refer to the pH measured immediately after the application of the products, i.e., at time 0. In the previous version of Figure 2, however, the first recorded measurement corresponded to the pH value observed after one day of artificial degradation. The graph, in fact, displays measurements taken on days 1, 4, 11, 26, 57, and 128.
Initially, time 0 was excluded for clarity reasons, as its inclusion would have compressed the data along the y-axis and made the point visually indistinguishable from that of day 1 on the x-axis. The updated graphical representation now allows for a more complete and detailed reading of the pH evolution from the very first stages of the treatment.
However, in accordance with the comments received, Figures 2, 3, and 4 have been modified to include the value at time zero and to adopt a logarithmic scale on the x-axis.
Comment 4: Lines 128-131: "The specimens were subjected to an artificial ageing cycle in a ventilated oven at a constant temperature of 60°C and in a room temperature chamber with a relative humidity of 90%" . Two different steps? But then in Figs 1-3 the Authors report the check of the pH throughout the artificial ageing process: what process ventilated oven or room temperature chamber?
Response 4: In response to the reviewer’s comment, the authors have added a clarifying sentence to better explain the nature of the treatment protocol. The ageing process consisted in placing the samples for half of the time between each measurement in a humidification chamber at room temperature, and for the other half in a ventilated oven maintained at 60 °C. From an operational perspective, the total duration of the treatment was calculated accordingly.
This approach was deliberately adopted to allow for the observation and objective assessment of the behaviour of the deacidifying agents under conditions that simulate realistic environmental fluctuations, specifically alternating periods of elevated temperature (associated with low relative humidity) and high humidity (at lower temperatures), as may occur in uncontrolled storage or display environments.
Comment 5: Figs. 8 and 9 are not reported at least in the version I received.
Response 5: The authors apologize for the inconvenience; the issue was likely due to a problem during the image upload process. All high-resolution images are, in any case, available in the supplementary materials. The authors have reinserted Figure 7 and 9 in the text (Figure 9 does not exist).
Comment 6: Due to the above described criticities I suggest the Authors to made new experiments, re-write the paper, and submit again a new paper to solve the strong weaknesses of the paper in the present form.
Response 6: The authors wish to express their appreciation for the constructive feedback received and believe they have carefully and comprehensively addressed all the concerns and observations raised, providing the necessary clarifications and revisions throughout the manuscript
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
Comments and Suggestions for AuthorsTo my opinion, the article is now very clear and can be published.
Author Response
The autors thank the referee for his work.
Reviewer 3 Report
Comments and Suggestions for AuthorsComment on Response 1.
I totally agree about the concept of concentration: it is obvious! During each conservation procedure that involves the use of solutions/dispersions at a certain concentration (correctly an intensive property), it is fundamental to specify two other properties, besides the concentration, of the applied solution/dispersion: (i) modality of application (and the Authors specify two different modalities, namely spray and brush), and (ii) amount of the solution/dispersion applied in volume, from which it easily deducible the amount in mole or weight of the solute/dispersed material, that normally is the active agent for the desired conservation treatment (cleaning, consolidation, protection, deacidification, etc.). From this second datum, knowing the the application surface, it is possible to deduce another important datum, which is the amount of the active agent applied on a square centimetre of surface. This amount, expressed as an example in mg/cm2, is not “simply an expression of the concentration on a thin layer”: it is the amount in mg of the active agent – in our case MgO or Ca(OH)2 – applied on 1 cm2 of surface to be treated. It is equally obvious that the guidelines for the application given by the supplier cannot contain the amount of the solution/dispersion to be applied, since it strictly depends on the conservation status, the type of support, the environmental conditions, and other parameters changing from a situation to another one. I believe that the Authors should stress in a part of the paper – where they believe it is better – that this datum is important and that “the quantities applied on the same surfaces were not identical, precisely because different application methods were use”. On the other hand, “this choice was intentional and motivated by the desire to simulate an in operando condition, that is, an application carried out by a conservator according to the operational guidelines provided by the manufacturers of the tested products”.
Comment on Response 2.
I appreciated the tentative explanation for the good performance of NE3P (I suggest to change the label in NE3B and from NP3P to NP3B, since if S refers to Spray, I believe for Brush it would be better adopt B), but I think this explanation should be added along the text, specifying what the Authors state in the Response 2 as follows or in a similar form. “Regarding the positive result observed for the NE3B treatment compared to the other three Nanorestore Paper® treatments, a possible explanation could be the higher volatility of ethanol with respect to 2-propanol, which altered the stability of the dispersion on the brush, thereby reducing the amount of nanoparticles transferred to the textile support, due to its adsorption onto the brush bristles. This suggests that during application it is fundamental not only to select the appropriate application procedure, but also to possibly change the concentration of the dispersion purchased by the supplier by diluting it when the dispersant medium is 2-propanol”.
A possible easy experiment to test if the tentative explanation is correct could be to do the same application with diluted NP3B until reaching the same pH as for NE3B: in this way not only the explanation could be confirmed, but also the approximate amount of nanoparticles remained entrapped within the bristles.
Comment on Response 3.
Thanks for clarifying with the new figure. In my opinion it should more correct to put as x-axis label simply Days, since the logarithmic scale is evident.
Comment on Response 4.
Thanks for the clarification. Now it is OK:
Comment on Response 5.
Thanks for adding the figures. In both figures I cannot succeed in reading the bar in micron, so that it is impossible to deduce the magnification. In Fig. 7 the addition on the micrograph of some boxes (circles or rectangles) indicating the agglomeration claimed would help the reader.
Comment on Response 6.
In my opinion the manuscript could be further improved addressing the issues described in the previous comments to responses. Indeed, the Authors have carefully and comprehensively addressed all the concerns and observations raised, but in some cases only in the responses to the Reviewer than in the paper. They should try to address the issues also in the manuscript before publication.
Final Comment.
I think that the Authors should specify better in the conclusions not only the right precautions against too strong alkalinity, but also the powerful of Nanorestore for preventive conservation during the 128 days of the simulation. Moreover, they should stress about the possibility to overcome the problem of the high pH at time = 0 by adjusting the correct concentration of the dispersion. Finally, I see that this quite strong alkaline pH (for three Nanorestore application over four) lasts only for one day over the whole simulation period: since the Authors correctly warn for possible damage in terms of azurite degradation and cellulose depolymerisation, they equally correctly should demonstrate whether this short time at pH > 9 is critical against the possible degradation mechanisms or not.
Author Response
Reviewer 3
Comment on Response 1. I totally agree about the concept of concentration: it is obvious! During each conservation procedure that involves the use of solutions/dispersions at a certain concentration (correctly an intensive property), it is fundamental to specify two other properties, besides the concentration, of the applied solution/dispersion: (i) modality of application (and the Authors specify two different modalities, namely spray and brush), and (ii) amount of the solution/dispersion applied in volume, from which it easily deducible the amount in mole or weight of the solute/dispersed material, that normally is the active agent for the desired conservation treatment (cleaning, consolidation, protection, deacidification, etc.). From this second datum, knowing the the application surface, it is possible to deduce another important datum, which is the amount of the active agent applied on a square centimetre of surface. This amount, expressed as an example in mg/cm2, is not “simply an expression of the concentration on a thin layer”: it is the amount in mg of the active agent – in our case MgO or Ca(OH)2 – applied on 1 cm2 of surface to be treated. It is equally obvious that the guidelines for the application given by the supplier cannot contain the amount of the solution/dispersion to be applied, since it strictly depends on the conservation status, the type of support, the environmental conditions, and other parameters changing from a situation to another one. I believe that the Authors should stress in a part of the paper – where they believe it is better – that this datum is important and that “the quantities applied on the same surfaces were not identical, precisely because different application methods were use”. On the other hand, “this choice was intentional and motivated by the desire to simulate an in operando condition, that is, an application carried out by a conservator according to the operational guidelines provided by the manufacturers of the tested products”.
Response 1. The authors, in agreement with the reviewer, have added to the text that the quantities applied on the same surfaces were not identical, as different application methods were used.
Comment on Response 2. I appreciated the tentative explanation for the good performance of NE3P (I suggest to change the label in NE3B and from NP3P to NP3B, since if S refers to Spray, I believe for Brush it would be better adopt B), but I think this explanation should be added along the text, specifying what the Authors state in the Response 2 as follows or in a similar form. “Regarding the positive result observed for the NE3B treatment compared to the other three Nanorestore Paper® treatments, a possible explanation could be the higher volatility of ethanol with respect to 2-propanol, which altered the stability of the dispersion on the brush, thereby reducing the amount of nanoparticles transferred to the textile support, due to its adsorption onto the brush bristles. This suggests that during application it is fundamental not only to select the appropriate application procedure, but also to possibly change the concentration of the dispersion purchased by the supplier by diluting it when the dispersant medium is 2-propanol”.
Response 2. The authors have updated the sample nomenclature, in accordance with the reviewer’s suggestions. As for the potential differences in concentration, both in the pristine conditions and following the application methods used, these fall within the scope of the guidelines provided by the manufacturers, while, as already stated, the focus of the present work lies on the application side, that is, on those who actually use the various products in operational contexts, namely conservators.
Comment on Response 3. Thanks for clarifying with the new figure. In my opinion it should more correct to put as x-axis label simply Days, since the logarithmic scale is evident.
Response 3. The authors have revised the name of the axis.
Comment on Response 4. Thanks for the clarification. Now it is OK:
Comment on Response 5. Thanks for adding the figures. In both figures I cannot succeed in reading the bar in micron, so that it is impossible to deduce the magnification. In Fig. 7 the addition on the micrograph of some boxes (circles or rectangles) indicating the agglomeration claimed would help the reader.
Response 5. The reviewer is probably referring to Figure 8 (where agglomeration can be observed). It is difficult to add circles or boxes, as the deposited particles are visible on nearly all the fibres (they appear as white spots present on each fibre). The caption has been revised accordingly.
Comment on Response 6.
In my opinion the manuscript could be further improved addressing the issues described in the previous comments to responses. Indeed, the Authors have carefully and comprehensively addressed all the concerns and observations raised, but in some cases only in the responses to the Reviewer than in the paper. They should try to address the issues also in the manuscript before publication.
Response 6. Even though most of the responses given to the reviewer were already included in the article, authors have incorporated other parts of the responses directly into the text in order to better explain and support the choices made.
Final Comment. I think that the Authors should specify better in the conclusions not only the right precautions against too strong alkalinity, but also the powerful of Nanorestore for preventive conservation during the 128 days of the simulation. Moreover, they should stress about the possibility to overcome the problem of the high pH at time = 0 by adjusting the correct concentration of the dispersion. Finally, I see that this quite strong alkaline pH (for three Nanorestore application over four) lasts only for one day over the whole simulation period: since the Authors correctly warn for possible damage in terms of azurite degradation and cellulose depolymerisation, they equally correctly should demonstrate whether this short time at pH > 9 is critical against the possible degradation mechanisms or not.
Response to Final Comment. As already extensively clarified, the authors do not aim to assess the effectiveness of one product over another, nor to encourage any commercially driven comparison. The present study focuses on the analysis of data obtained from the practical application of materials commonly used in conservation, and on the associated chemical implications (such as pH variation and chromatic alteration). These parameters are routinely monitored in standard restoration practice.
Regarding the potential effects of high alkalinity on substrates, as well as on preparatory layers, pigments, and varnishes, an extensive scientific literature is available, addressing both the kinetics and the mechanisms of degradation.
Author Response File: Author Response.pdf
Round 3
Reviewer 3 Report
Comments and Suggestions for AuthorsI appreciated the efforts by the Authors to address my issues. The paper appears to me to be publishable in the present revised form. Nevertheless, I believe, for the reasons already mentioned in my two previuos reports, that the quality of the paper remains in the rating suggested during the first revision process, i.e. between low and average.
