Spectral- and Image-Based Metrics for Evaluating Cleaning Tests on Unvarnished Painted Surfaces

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The paper is focused on a range of cleaning efficacy and homogeneity evaluation metrics for assessing cleaning trials on unvarnished painted surfaces, by applying different imaging techniques (VIS, VNIR, SWIR, FTIR, MIR, SEM-EDX) complemented by appearance measurements (glossimetry and colorimetry).

The aim is to face the issue of possible subjective evaluations of surface cleaning tests in conservation and restoration interventions.

 

The topic falls within the Aims & Scopes of the Journal, mainly regarding “Characterization techniques”, “Theoretical and computational modeling of surfaces and interfaces”, “Processes for coating deposition and modification”, and “Applied surface science” areas.

 

The introductory section correctly positions the scientific issue addressed in a critical-analytical dimension, considering subjectivity and objectivity, perceptual and contextual aspects, and disomoegenity in cleaning studies. 

One of the most critical issues in dealing with cleaning surfaces belonging to cultural heritage (whether it is possible to rely on objective criteria) is addressed, highlighting the uniqueness of each cultural heritage and each conservation situation, and tracing the scientific problem back to the integration of the necessary know-how of expert conservators with empirical analytical data.

 

Section “2. Materials and Methods” explains the case studies on which the methodology is experimented, mock-ups based on material analysis of Munch’s painting “Kjemi” and designed to study the agar gel spray cleaning technique for unvarnished, water-sensitive painted surfaces as a response to the soiling of the paintings within the Aula, and to test the applicability and suitability of the imaging techniques for the documentation of the cleaning trials.

All the details related to the simulation of mechanical and water-sensitive properties of the Aula paintings and for artificial soiling are clearly described, as well as agar gels preparations with the different cleaning solutions, and applications.  

Treatment evaluation metrics and scoring criteria are explained.

-        It is suggested to add a short explanation of ImageJ, mentioned for the first time at line 199 without any description as application for image processing.

 

In section “3. Results and discussion” image- and spectral-based metrics are discussed, listing measured properties for each metric inputted into the normalised difference equation used to calculate cleaning efficacy (image-based, appearance, spectral-based).

 

The references section is comprehensive, up-to-date and consistent with the topics covered. Out of 126 references, 56 are within the last 5 years, 17 are by the authors.

 

Overall, the paper presents the research, experimentation, objectives and results in a very clear manner, also addressing the critical-interpretative issues that usually are the limits in hyper-scientific applications on cultural heritage, when the interpretative needs of specific results on the basis of data that must go beyond numerical-analytical ones are lost sight of.

 

Minor comments

Check throughout the paper that all acronyms are “expanded” the first time they appear.

 

In the reviewer's opinion, the paper is accepted with very very minor revisions (general checking).

Author Response

Please see the attachment.

Author Response File: Author Response.docx

Reviewer 2 Report

Comments and Suggestions for Authors

 

Regarding the manuscript “Spectral- and image-based metrics for evaluating cleaning tests on unvarnished painted surfaces” submitted for consideration by MDPI Coatings.

The paper is focused on finding a range of cleaning efficacy and homogeneity evaluation metrics for appraising cleaning trials by measuring quantifiable changes in the appearance and characteristic spectral properties of surfaces. The metrics are on imaging techniques (optical imaging by photography), spectral imaging in the visible-to-near-infrared  and shortwave infrared ranges, chemical imaging by Fourier transform infrared spectral mapping in the mid-infrared range; and scanning electron microscopy coupled with energy dispersive X-ray spectroscopy element mapping.

The article “Spectral- and image-based metrics for evaluating cleaning tests on unvarnished painted surfaces is interesting and relevant from both fundamental and practical points of view.

 The introduction section brings the knowledge of cleaning up to date. More details are need.

I recommend to the authors to pay attention also to biocleanig and so add biocleaning information with enzymes entrapped in agar gel (Gomoiu I.et al., 2022, Biocleaning  of wall painting with microbial esterases immobilised in agarart, , Romanian Journal of Materials,52, 3, 238-251or with bacteria cells (G. Ranalli, et al, Onsite advanced biocleaning system for historical wall paintings using new agar‐gauze, Journal of applied microbiology, 2019, 126(6),1785). Gels are also used for cleaning of mortars (Gomoiu I. et al, 2020, Cleaning of mural paintings and mortars: review, Romanian Journal of Materials,50, 4, 485-492), archaeological metals (T. Giraud et al. , Use of gels for the cleaning of archaeological metals. Case study of silver-plated copper alloy coins, Journal of Cultural Heritage, 2021, 52, 73) or starch (H.E. Ahmed, F. N. Kolisis, An Investigation into the Removal of Starch Paste Adhesives from Historical Textiles by Using .the Enzyme α-Amylase, Journal of Cultural Heritage, 2011,12, 169).

Based on literature, the authors elaborated Example of cleaning criteria used in conservation studies, which is very important for artworks.

The manuscript reading is fluid, and I did not find difficult to follow the arguments. The experimental design is appropriate to achieve the goals.

Materials and Methods section are very well described and in detail.

The authors applied Agar gels as a direct spray and as a pre-formed rigid film.

I recommend to the authors to mention if the surface was contaminated (by microorganisms) or not. As a rule, agar spray is not used on a contaminated surface.

Results are the expression of the application of advanced methods and are scientifically interesting and important for artworks.

All metrics used by authors aimed to semi-quantitatively compare treatment results to aid in decision-making in a reproducible and shareable manner, and to complement professional observations made by eye. This could be a suggestion for restores.

I recommend to the authors:

- To explain why Cleaning efficacy results for images taken at microscale coincided better with visual observations than those taken at macroscale

- If it is correct the multidisciplinary approaches presented expand on the means currently available to conservators for empirically evaluating cleaning tests within a treatment context, please explain or to mention to perform a scientific cleaning in order to avoid empirical cleaning.

- Future research directions should be also clearly be mentioned.

- The conclusions section to be clear and concise.

 

Comments for author File: Comments.pdf

Author Response

Please see the attachment.

Author Response File: Author Response.docx