Chemical Composition and Micro Morphology of Golden Laminae in the Wall Painting “La Maestà” by Simone Martini: A Study by Optical Microscopy, XRD, FESEM-EDS and ToF-SIMS
, Andrea Scala 2, Marco Giamello 2, Marianna Uva 3, Riccardo Maria Pulselli 4 and Nadia Marchettini 5Round 1
Reviewer 1 Report
The article entitled “Chemical composition and micro morphology of golden laminae in the wall painting la maestà by Simone Martini: a study by Optical Microscopy, XRD, FESEM-EDS and ToF-SIMS” by Atrei et al. is an interesting application of modern analytical techniques to study the complex stratigraphy of gilding samples of the Italian 14th century.
The work is well organized and clear in all parts. I would suggest its publication after minor revisions.
Minor issues:
1) Abstract: Please use “glue” instead of “stick”. This change must be performed all over the article text.
2) Abstract lines 23-24. Please use the past tense of “show” and “consist” verbs as it was done in the rest of the text.
3) Line 99: what does “pf” mean?
4) Line 108: please change “conclusions” with “results”
5) Lines 110-112. I think there is something wrong in this part. Two times is indicated the thickness of the gold/metallic lamina: “below 5 micorns” and “2 to 5 microns”. Please keep only one value.
6) The magnification of figures 2a and 2b is too low to appreciate the gold lamina. Please couple these images with two at higher magnification. Moreover, authors should report in the article text if EDX was carried out as “spot analysis” or “area analysis”. I suppose that for the bulk, an area was chosen. Please report the dimension of that area in the article text as well as in figure (i.e dashed rectangular area).
7) Lines 131-132: figure caption is wrong. I think that figure 2a regards sample A, not B as indicated.
8) Line 154: Please change “close to those the elements…” with” ascribable to the chemical elements detected by EDX analysis”.
9) Lines:200-203: please indicate in figure caption that figures are of sample A.
10) Lines 205-207: Elements detected are not due to contamination but are ascribable to the bole /ground layer composition. Earth pigments are commonly found in this case which are constituted of Al, and Ca minerals. This is commonly found. Please give another explanation.
11) Line 217: actually I think that copper as well is a part of the gilding as an impurity.
12) Line 223: Actually Figure 5c does not exist
13) Line 225: “and the tin lamina” is repeated twice
14) Figure 5: please indicate if EDX was performed as a “spot” or “area” analysis. See issue 6.
15) Figure 6: the overlay picture does not show the red color (Sn) and the green color (Ag) but yellow color instead. This is strange. Please check if something is wrong.
16) Line 350: Actually, looking at the ToF-SIMS maps (figure 6b) Ag appears significant also in the Au layer. Please discuss this issue.
Author Response
We revised the paper according to the comments of the referees. The changes in the revised text are marked we in yellow.The list of the action taken in response to the comments of reviewer #1 is reported below.
Please note, that the number of lines in the reports of the reviewers refer to the original version of the paper while those used in the answer refer to the revised version.
Reviewer #1
1) Abstract: Please use “glue” instead of “stick”. This change must be performed all over the article text.
We changed the text according this comment
2)Abstract lines 23-24. Please use the past tense of “show” and “consist” verbs as it was done in the rest of the text.
We changed the text according this comment
3) Line 99: what does “pf” mean?
The mistyping has been corrected
4) Line 108: please change “conclusions” with “results”
We changed the text according this comment
5) Lines 110-112. I think there is something wrong in this part. Two times is indicated the thickness of the gold/metallic lamina: “below 5 micorns” and “2 to 5 microns”. Please keep only one value.
The first value refers to the average thickness (which is below 5 microns) whereas the other values concern the thickness of the leaf which varies from 2 to 5.
6) The magnification of figures 2a and 2b is too low to appreciate the gold lamina. Please couple these images with two at higher magnification. Moreover, authors should report in the article text if EDX was carried out as “spot analysis” or “area analysis”. I suppose that for the bulk, an area was chosen. Please report the dimension of that area in the article text as well as in figure (i.e dashed rectangular area).
It seems that the gold foil is visible in the OM image. We believe that adding another image would make the Figure 2 too crowded. As requested by the referee the analysed areas by EDX are now specified (caption of Figure 2)
7) Lines 131-132: figure caption is wrong. I think that figure 2a regards sample A, not B as indicated.
The mistake in the figure caption has been corrected.
8) Line 154: Please change “close to those the elements…” with” ascribable to the chemical elements detected by EDX analysis”.
We changed the text according to the comment of the referee
9) Lines:200-203: please indicate in figure caption that figures are of sample A.
In the caption of Figure 2 (a) it is now specified that the results are for sample A.
10) Lines 205-207: Elements detected are not due to contamination but are ascribable to the bole /ground layer composition. Earth pigments are commonly found in this case which are constituted of Al, and Ca minerals. This is commonly found. Please give another explanation.
Surface contamination of the sample is responsible for the observation of ion fragments of hydrocarbons in the ToF-SIMS specta. The sentence has been modified to clarify this point (lines 158-160).
11)Line 217: actually I think that copper as well is a part of the gilding as an impurity.
We agree that copper can be an impurity in the gold foil but we did not have a clear evidence for the presence of Cu in the gilding lamina.
12) Line 223: Actually Figure 5c does not exist
This error has been corrected
13) Line 225: “and the tin lamina” is repeated twice
This error has been corrected
14) Figure 5: please indicate if EDX was performed as a “spot” or “area” analysis. See issue 6.
This information is now reported in the caption of Figure 5
15) Figure 6: the overlay picture does not show the red color (Sn) and the green color (Ag) but yellow color instead. This is strange. Please check if something is wrong.
It seems to be correct. By adding red and green lights, yellow light is obtained.
16) Line 350: Actually, looking at the ToF-SIMS maps (figure 6b) Ag appears significant also in the Au layer. Please discuss this issue.
Indeed, the signal of silver is rather weak and the noise tends to blur to image. In the text it is specified that signal of silver, although visible on the gold leaf, is localized mainly on the tin lamina (line 230).
Reviewer 2 Report
Atrei and coworkers propose an interesting case study where two different gilding techniques were used to decorate a part of the “Sala del Mappamondo” in the city hall in Siena. The wall painting “La Maestà” is attributed to Simone Martini and dated back to the 14th century. A multi-analytical approach comprising OM, XRD, FESEM-EDS, and ToF-SIMS was used to investigate two kinds of gilding. The paper is well organized and written, and I think it can be published after considering the following minor comments.
P1 L9-13: Author’s affiliations are incorrectly listed
P2 L63-65: Please, specify magnification used for OM observations.
P2 L68: Report details about EDS system.
P2 L72-76: Please, provide experimental details such as lambda, angular range, step size and sampling time.
P3 L89: To avoid confusion in the reader, sampling points marked with circles (1-7) should be removed from figure 1.
P3 L99: The OM pf thin section….. What do the authors mean by the term OM pf ?
P5 Figure3: What about XRD signals for yellow ochres?
P6 Figure 4: Could be useful provide a schematic representation of the stratigraphy, showing in the total ion image where the preparation layer and gold leaf are located.
P6 Figure 4: Add a color scale bar indicating the ion intensity.
General: m/z values of the isotopes are usually not reported.
P7 L232: Can the authors argue something from the fact that silver is localized in the tin lamina? This could be an interesting detail regarding the gilding technique.
P7 L238: Fluorinated polymers were usually adopted as protecting coatings in metal artifacts (waterproofing). This point should be highlighted in order to help restorers and conservators in designing possible restoration projects.
P8 Figure 6: The authors can try to use a sort of a contour map to describe the stratigraphy. Alternatively, a snapshot from the ToF-SIMS microcamera view could be useful for the reader to localize ground layer and gold lamina in the ion maps.
Author Response
We revised the paper according to the comments of the referees. The changes in the revised text are marked we in yellow.The list of the action taken in response to the comments of reviewer #2 is reported below.
Please note, that the number of lines in the reports of the reviewers refer to the original version of the paper while those used in the answer refer to the revised version.
L9-13: Author’s affiliations are incorrectly listed
We checked the list of affiliations and it is correct. An error in the postal code of one affiliation has been corrected.
P2 L63-65: Please, specify magnification used for OM observations.
Since a bar showing the length of 50 microns is shown there is no need to specify the magnification which is about 300 times.
P2 L68: Report details about EDS system.
The details about the EDS system are reported (line 68)
P2 L72-76: Please, provide experimental details such as lambda, angular range, step size and sampling time.
The details about the XRD measurements are now reported (line 77).
P3 L89: To avoid confusion in the reader, sampling points marked with circles (1-7) should be removed from figure 1.
In Figure 1, all the sampling points are shown but the samples (A and B) for which the results of the analysis are presented are marked in a different way to avoid confusion.
P3 L99: The OM pf thin section….. What do the authors mean by the term OM pf ?
The mistyping has been corrected
P5 Figure3: What about XRD signals for yellow ochres?
We added a sentence to explain this point (line 151)
P6 Figure 4: Could be useful provide a schematic representation of the stratigraphy, showing in the total ion image where the preparation layer and gold leaf are located.
A dashed white line to localize the gold leaf has been drawn on the total ion image, as suggested by the referee.
P6 Figure 4: Add a color scale bar indicating the ion intensity.
General: m/z values of the isotopes are usually not reported.
Instead of the a color scale bar, the total count rates for the peaks of Ag and Au are now reported in the caption of Figure 4 (line 210). The m/z values are reported in the text.
P7 L232: Can the authors argue something from the fact that silver is localized in the tin lamina? This could be an interesting detail regarding the gilding technique.
A sentence has been added to discuss this point (line 231)
P7 L238: Fluorinated polymers were usually adopted as protecting coatings in metal artifacts (waterproofing). This point should be highlighted in order to help restorers and conservators in designing possible restoration projects.
We agree with the reviewer and it is remarkable that ToF-SIMS is able to reveal these compounds.
P8 Figure 6: The authors can try to use a sort of a contour map to describe the stratigraphy. Alternatively, a snapshot from the ToF-SIMS microcamera view could be useful for the reader to localize ground layer and gold lamina in the ion maps.
A white dashed line was drawn in Figure 6 to trace the zone of the tin lamina, useful for the reader to localize the preparation layer and the gold leaf in the ion maps.
Reviewer 3 Report
The work of Atrei et al is dedicated to the analysis of the wall painting “La Maestà” samples by microscopy and spectroscopy techniques. Paint layer structure was determined by optical and scanning electron microscopy. EDX analysis showed ratio of the main inorganic compounds in the paint. However additional time-of-flight secondary ion mass spectrometry imaging allows to detect metal traces that were not detected by EDX. As it was shown by Atrei et al it ToF-SIMS can be beneficial approach for sample characterization. Several issues should be corrected before publication:
1) Examples of ToF-SIMS studies of artwork objects should be given in more details in Introduction.
2) P. 2, L. 70. The device for sample coating should be specified.
3) P. 2, L. 79 Gold liquid metal ion guns are known to produce several ion species. Which one was used (Au1+ or Au3+). Also if electron flood gun was activated it should be stated in the text.
4) Fig. 4 should be revised. It is unclear what area is analyzed (compare with fig.5 where it is obvious). What is from the left side and right side of gold lamina? Hence it is recommended to replace fig. 4a by optical image of the analyzed sample. Alternatively it can be replaced by sample outline. Figure caption also should be corrected.
5) P.7. L. 216. “However, an 214 upper limit of ca. 1 at % to the silver concentration is a reasonable estimation since the signal of silver 215 was not detectable by EDX” The statement is not obvious. Either it should be clarified in details or reference should be provided.
6) P. 7. L. 243. “The peaks corresponding to the ion fragments of lead palmitate and stearate were also detected.” Did authors tried to measure the same area in negative secondary ions? Palmitic and steraric acids has m/z 255 and 283 respectively. Also It would be interesting if unsaturated fatty acids are present in the spectrum.
7) P. 7. L. 243. “Palmitic and stearic acids are the oxidation and hydrolysis products of linseed and other unsaturated oils during ageing of the original materials, as shown in many studies on oil painting ageing” Authors should clarify what kind of fatty acids they mean: free fatty acids or fatty acid fragments produced by ion bombardment.
Author Response
We revised the paper according to the comments of the referees. The changes in the revised text are marked we in yellow.The list of the action taken in response to the comments of reviewer #3 is reported below.
Please note, that the number of lines in the reports of the reviewers refer to the original version of the paper while those used in the answer refer to the revised version.
1) Examples of ToF-SIMS studies of artwork objects should be given in more details in Introduction.
Since it is not meant to be a review paper, we believe that the cited papers provide an overview of ToF-SIMS applied to cultural heritage studies (references 5, 8, 9, 10, 11, 15)
2) P. 2, L. 70. The device for sample coating should be specified.
This information is now reported (line 71).
3) P. 2, L. 79 Gold liquid metal ion guns are known to produce several ion species. Which one was used (Au1+ or Au3+). Also if electron flood gun was activated it should be stated in the text.
The required details are now reported (line 82-86).
4) Fig. 4 should be revised. It is unclear what area is analyzed (compare with fig.5 where it is obvious). What is from the left side and right side of gold lamina? Hence it is recommended to replace fig. 4a by optical image of the analyzed sample. Alternatively it can be replaced by sample outline. Figure caption also should be corrected.
Figure 4 has been modified by marking the zone of the gold leaf and the figure caption modified accordingly.
5) P.7. L. 216. “However, an 214 upper limit of ca. 1 at % to the silver concentration is a reasonable estimation since the signal of silver 215 was not detectable by EDX” The statement is not obvious. Either it should be clarified in details or reference should be provided.
The quoted upper limit the silver concentration should be considered as a rough estimation. A reference to a book on EDX analysis has been added (line 170).
6) P. 7. L. 243. “The peaks corresponding to the ion fragments of lead palmitate and stearate were also detected.” Did authors tried to measure the same area in negative secondary ions? Palmitic and steraric acids has m/z 255 and 283 respectively. Also It would be interesting if unsaturated fatty acids are present in the spectrum.
ToF-SIMS spectra measured collecting negative ions showed peaks which could attributed to deprotonated palmitic and stearic acids. A sentence has been added to clarify this point (line 243) However, as discussed in the text, the altered state of the organic materials did not permitted an univocal evidence for the presence of these compounds.
7) P. 7. L. 243. “Palmitic and stearic acids are the oxidation and hydrolysis products of linseed and other unsaturated oils during ageing of the original materials, as shown in many studies on oil painting ageing” Authors should clarify what kind of fatty acids they mean: free fatty acids or fatty acid fragments produced by ion bombardment.
According to the studies by mass spectrometry of oil painting samples, palmitic and stearic acids are the products of the oxidation and hydrolysis of linseed oil or other oils.
Reviewer 4 Report
The paper describes in a convincing manner the gold decoration on a wall painting. There are some minor observations, which should be revised:
The analytical methods deserve more attention. Few is said about the analytical conditions, for instance for FESEM and micro-XRD. For chemical analyses, the limits of detection and standards used are missing. Especially the ToF-SIMS deserves more attention as it is not a very commonly used method. What is m/z?
Figure 2: in the text it is stated that the thickness of preparation layer is in average 150 microns. However, in the image the preparation layer is much larger than 200 microns. mXRD: the lines which are attributed to "white lead' seem to be the lines of hydrocerussite. In any case, there is no minerals called white lead. This is either cerussite (PbCO3) or a mixture of cerussite (PbCO3) and hydrocerussite (Pb3(CO3)2(OH)2 Figure 2a shows a very inhomogeneous preparation layer, with at least 5 different components. This can be seen also in Figure 2b (which is not a FESEM image but, most likely, a back scattered electron image). Thus, something is not O.K. with the XRD if it shows only Pb-compounds. Or, the mXRD was collected exclusively on a small grain of 'white lead". This should be clarified. In fact Figure 2b spectrum shows clearly Fe, ca, K, Al and Si as compounds. These compounds were not addressed in the text. Line 207-208: "The peaks of the isotopes of Cu+(m/z 207 62.9 and 64.9) and of Pb+ (m/z 206.0, 207.0 and 298.0) are observed, in agreement with the EDX results". COMMENT: I do not see any EDX results so far. Line 220: 'sample B' not 'samples B'. Or are more B samples?
Author Response
Authors' Responses to Reviewer's Comments (Reviewer 4)
Author's Notes
We revised the paper according to the comments of the referees. The changes in the revised text are marked we in yellow.The list of the action taken in response to the comments of reviewer # 4 is reported below.
Please note, that the line numbers in the reports of the reviewers refer to the original version of the paper while those used in the answer refer to the revised version.
Reviewer #4
The analytical methods deserve more attention. Few is said about the analytical conditions, for instance for FESEM and micro-XRD. For chemical analyses, the limits of detection and standards used are missing. Especially the ToF-SIMS deserves more attention as it is not a very commonly used method. What is m/z?
Additional details about the FESEM-EDX, XRD and ToF-SIMS measurements have been added (Lines 68-71, 77 and 82-86). ToF-SIMS is not a quantitative technique and the limits of detection cannot be defined since they strongly depend on the chemical chemical state of the species which are analysed. In the case of EDX we added a citation to a book about chemical analysis by EDX (Ref. 16). m/z is ratio of the mass of the ion (in atomic mass unit) to the charge of the ion. In ToF-SIMS, as in all mass spectrometry methods, ions are separated on the basis of the different m/z ratios.
Figure 2: in the text it is stated that the thickness of preparation layer is in average 150 microns. However, in the image the preparation layer is much larger than 200 microns.
Indeed, 150 microns is the average thickness of the preparation layer. The OM image in Figure 2 was taken in a region were the thickness is much larger than the average.
mXRD: the lines which are attributed to "white lead' seem to be the lines of hydrocerussite. In any case, there is no minerals called white lead. This is either cerussite (PbCO3) or a mixture of cerussite (PbCO3) and hydrocerussite (Pb3(CO3)2(OH)2
White lead is the name of the white pigment 2Pb(CO3)2 Pb(OH)2 (caption of figure 3), a hydroxy carbonate of Pb, which occurs naturally as a mineral named hydrocerussite. For this reason, as the referee wrote, the lines of white lead are the same of hydrocerussite
Figure 2a shows a very inhomogeneous preparation layer, with at least 5 different components. This can be seen also in Figure 2b (which is not a FESEM image but, most likely, a back scattered electron image). Thus, something is not O.K. with the XRD if it shows only Pb-compounds. Or, the mXRD was collected exclusively on a small grain of 'white lead". This should be clarified.
Indeed, the preparation layer is inhomogeneous, containing grains of various materials as shown by the OM and FESEM images. The XRD measurements were performed on the entire preparation layer. The diffractogram is dominated by the peaks of white lead and Pb3O4 and probably those of yellow ochres are too weak to be detected. A sentence has been added to explain this point (line 151). On the other hand the aim of the XRD measurements was to identify the components containing lead.
Figure 2b spectrum shows clearly Fe, ca, K, Al and Si as compounds. These compounds were not addressed in the text
These elements (see table 1 and text, lines 38 and 121) are present in the preparation layer which is a mixture of clays, iron oxides and hydroxides.
Line 207-208: "The peaks of the isotopes of Cu+(m/z 207 62.9 and 64.9) and of Pb+ (m/z 206.0, 207.0 and 298.0) are observed, in agreement with the EDX results". COMMENT: I do not see any EDX results so far.
The results of the EDX analysis are always presented and discussed before those obtained by ToF-SIMS. For instance for sample A, EDX results in Table 1: Line 139). Presentation of ToF-SIMS results (line 155).
Line 220: 'sample B' not 'samples B'. Or are more B samples?
"samples "is a mistyping. It has been corrected.
