A Study on Correggio Wall Paintings: Characterization of Technique and Materials of Abbey Church of S. Giovanni Evangelista in Parma, Italy

Round 1

Reviewer 1 Report

This paper should be a reference on scientific studies related to one of the most important artist´s worldwide, during 16th century. The proposal is of an huge interest, exposed in abstract. However, the paper should be improved in several aspects.

The introduction encompasses a general overview on previous research about this artist, revealing also past interventions.

Proposal goals with this reasearch are based on scientific support to the intervention actions. Althought it was highlight: “painting technique, the state of preservation, the possible additions made during previous restorations and also the current decay processes”, the paper needs more improvements and detailed informations.

In order to understand these goals, I recommend that authors include imaging techniques (UV images/ and other imaging exams used for diagnosis).

Details about the artistic execution used by this master is needed and to better understand the technique of artistic production the authors should mount the samples in cross-sections and then identify the layers build-up and pigments mixtures. Can the authors justify why they didn´t do it?

If authors want to keep this paper structure they should say that they analysed pigments and binding media.  They only identified the main technique, secco, but not the artistic processes envolved in the paint execution.

There are other aspects that can be improved (missing information and paper structure):

1. Proposal goals with this reasearch are based on scientific support to the intervention actions. However, in order to understand these goals, I recommend that authors include imaging techniques (UV images/ and other imaging exams used for diagnosis)
2. The figure 2 is presented in very low resolution, I encourage the authors to introduce a 300 dpi resolution image.
3. In table 1, the sampling points are indicated through the position of the scalpel and a type of tape. The use of this tape is hiding the sample points, and therefore I suggest, if possible, that the authors use the scalpel as a reference. If not possible, I would ask them to justify why they used this strategy.
4. Experimental part should include more detailed information about how the authors prepared the samples for the analysis and other few descriptions about experimental conditions (e.g. SEM-EDS Low vacum?/ images (BSE/ SE?)
5. Suggestion: Table 1 and table 2 can be set togheter, and the relationship between colours and sample points will be easily related to the materials identified. Authors can use figure 1 and 2 to identify sampling points in experimental part.
6. The results should also be justify/comproved with SEM-EDS and FTIR analysis, regarding the pigments identification. 70X magnification images made with optical microscope could be also included? SEM images could be also related to pigment´s morphology and pigments mixtures…e.g.
7. The authors should comment if the use of tape in sampling points can be related to the the presence of glue (detected by raman) and/or, on the other way, explain how did they performed the analysis to overcome this.
8. The paper can be enriched in references.

Author Response

THANK YOU FOR YOU SUGGESTION, THAT HAVE COMPLETED OUR PAPER

Author Response File: Author Response.docx

Reviewer 2 Report

The paper describes a scientific study of a beautiful 16th century wall painting by Correggio in the Church of S. Giovanni Evangelista in Parma. The authors used techniques fully consolidated in Heritage diagnostic research for the investigation of Correggio's painting materials and techniques. In particular, SEM-EDS and micro-Raman spectroscopy were used for pigments characterization and GC-MS and FT-IR spectroscopy for the analysis of organic binders and restoration/degradation products.

The manuscript is well written and the presentation of the techniques and the results achieved indicate that the chosen methods were suitable for the author's investigation purposes. In addition, some interesting details as Correggio’s technique “a secco” with a mixture of egg and animal glue as binding media and a particular use of cinnabar to mold the pigments palette, together with the general level of importance of studying a major Italian Renaissance painter as Correggio, make this paper worth publishing.  Nonetheless some suggestions for minor revisions are here proposed.

• First, just a brief methodological consideration about the number of samples: surely micro-sampling during restoration campaigns is often necessary and can be fairly done without a strong impact on the original pictorial layer, nonetheless it is worth asking to the authors if a reduced number of samples could have been preferred. Since no stratigraphic investigation was foreseen and considering only four samples were used for organic destructive GC-MS analysis (necessary to identify the organic binder), maybe some non-invasive portable methods as X-ray fluorescence could have been chosen for pigments identification instead of SEM-EDS and focusing Raman spectroscopy only where elemental data give no useful results (reasonably the cases of ultramarine and indigo blue). Could the authors discuss this choice?
• On page 12 a possible type error in the “laurite” word instead of “lazurite” (The presence of the same mixture of binders in samples B1, B7, B19 and B20, where Raman analysis evidenced laurite, smalt […]). Seems to be not intentional since the mineral laurite (RuS₂) is not mentioned elsewhere in the manuscript and not related to the context.
• In the Raman spectra in Fig.3, Fig.4, Fig.5 and Fig.6 it would be useful to associate the names of the samples related to the Raman spectra (it could be done directly on the image or in the figure captions).

Author Response

WE HAVE COMPLETED OUR PAPER

WE THANK FOR YOUR SUGGESTION

Author Response File: Author Response.docx

Round 2

Reviewer 1 Report

Thank you for your comments and upgrate.

My suggestions are:

- Justify in the text that you used UV imaging for diagnosis of state of conservation and for the selection of sampling points.

- justify in the texto, that at this stage you didn´t mount cross-sections and the methods used allowed comparison to previous studies regarding the anaysis of pigments and binding media

- In the comments you mentioned: “We wanted also to understand if we were facing fresco wall paintings, if there were areas made a secco and if these areas were due to the presence of pigments that require the use of organic binders for their application, such as azurite and malachite. We have certainly found the widespread presence of fresco painting, but we have identified the use of a secco technique, also with pigments, such as lazurite, smalt, hematite, green earth, goethite, that do not need the use of organic binding media on the wall.”

In fact, this is much clear now and you can improve your conclusion with this.

- About the sampling points, they are indicated through the position of the scalpel and a type of tape. My concern is also that the use of this tape is hiding the detail of the sample points. Do you have the record of this only with scalpel? And if you have 20X / 70X magnifications please, use it.

- Please, use another figure to include SEM-EDS results: the images obtained through BSE and the EDS analysis. In the method (experimental part) you should say how did you prepare the sample for the analysis (e.g. the analysis were performed in a fragment of a blue region, on the top of the sample, e.g., metal coating, SEM images in BSE/ SE mode).

- About my previous suggestion regarding Table 1 and table 2, that can be set together. I still think that they can be together and maybe an horizontal format can result. If possible, try to add also another column with 70X magnifications of the correspondent areas of sampling (details close to that).

Author Response

thank you for your suggestion

Author Response File: Author Response.pdf