New Evidence of Traditional Japanese Dyeing Techniques: A Spectroscopic Investigation

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This study provides insights into the production of Japanese folk textiles from the 19^th and 20 ^th centuries and is valuable for a deeper understanding of traditional Japanese dyeing techniques. However, a revision of the manuscript is necessary. In particular, some important literature references should be added and a table summarizing the spectral data should be inserted.

 

Page 2, line2 76-77: Botanical nomenclature (Polygonum tinctorium) - The abbreviated author's name should be added.

Page 2, line 87: Since the use of wisteria for the production of textiles is not so frequently described in the literature, the information should be further specified. Which Wisteria species were used for fiber extraction?

Page 3, line 102: The statement “The yarn generally received a previous mordanting step with tannins, or inorganic salts …“ is misleading. In the case of vat or direct dyeing, the use of tannins or inorganic salts is not necessary.

Page 3, lines 103-104: “…containing aluminium, iron or copper ions…" instead of “…containing aluminium, iron or copper…“

Page 3, lines 94-106: References to important literature such as those listed below are missing in this text section.

Cardon, D. Natural Dyes: Sources, Tradition, Technology and Science. Archetype Publications Ltd.: London, 2007. (e.g. pp. 379-386)

Page 4, line 164: ER-FTIR spectroscopy is mentioned for the first time in the text. In addition to the abbreviation ER, the full designation (External Reflection) should be given here. Subsequently, it is sufficient if the abbreviation is used. Please check the following text, as sometimes the abbreviation (ER-FTIR spectroscopy) and sometimes the full designation (External Reflection Fourier Transform Infrared spectroscopy or External reflection FTIR spectroscopy) is used.

Page 7, line 255: Please check the spelling - visible reflectance.

Page 7, line 255: SNV = Standard Normal Variate?

Pages 7-10: Were further minimally invasive investigations, e.g. using LC-MS/MS, carried out to confirm the results described in section 3.1? Have systematic studies been carried out on the influence of dye concentration and the presence of mordants on the reflectance spectra of the colorants under consideration?

The spectral data are currently discussed in several text sections and presented in several figures. An overview of the investigated colorants and the spectral data, e.g. in the form of a table, should be added.

Previous studies (see below for example) should also be considered when discussing the results.

Vermeulen M, Tamburini D, Müller EMK, Centeno SA, Basso E, Leona M. Integrating liquid chromatography mass spectrometry into an analytical protocol for the identification of organic colorants in Japanese woodblock prints. Scientific Reports. 2020;10(1):20921. doi:10.1038/s41598-020-77959-2

Page 8, line 281: Please add information on the colorants yamahaji and Hansa yellow (e.g. main coloring component). yamahaji = aqueous extract of Japanese sumac wood? Hansa yellow = synthetic dyestuff containing an azo group?

Page 11, lines 336-339: Spectral features of cotton reference and differentiation from bast fibers such as hemp, i.e. the absence of ligning signals should be briefly mentioned. Were additional microscopic examinations carried out on the plant fibers?

Page 12, line 360: Were characteristic marker bands for indigo at 1462 and 1482 cm^-1 also detected?

Author Response

We thank the reviewer for the positive feedback. He could grasp the meaning of our work and he raised some issues which have been solved improving the overall quality of the paper.

The references requested have been added, as well as the botanical information. The typos and the issue of the abbreviations have been solved. The spectral features which led to the identification of pigments and dyes are summarized in Table S1, available in the Supporting material. As for the other points, our answers follow.

Page 3, line 102: The statement “The yarn generally received a previous mordanting step with tannins, or inorganic salts …“ is misleading. In the case of vat or direct dyeing, the use of tannins or inorganic salts is not necessary.

We clarified the sentence, as follows (lines 104-107 of the revised manuscript):

“Except for vat or direct dyeing, the yarn generally underwent a prior mordanting step with tannins, or inorganic salts containing aluminium, iron or copper ions, which made the fibre-dye bond stronger and more durable, even influencing the final hue of the textile

Pages 7-10: Were further minimally invasive investigations, e.g. using LC-MS/MS, carried out to confirm the results described in section 3.1? Have systematic studies been carried out on the influence of dye concentration and the presence of mordants on the reflectance spectra of the colorants under consideration?

The owner of the collection did not grant us permission to take any samples from the objects under study, so the use of HPLC-MS was not considered. Conversely, the application of portable Raman spectroscopy or XRF could have provided complementary information, but these techniques were not available at the time of the analyses. As highlighted by much of the available literature, FORS or visible reflectance spectroscopy should be viewed as preliminary techniques, with results strengthened by other complementary portable or minimally invasive methods (Mounier 2018, Cesaratto 2018, Tamburini 2019, Tamburini 2020, Vermeulen 2020).

In this study, we used FTIR spectroscopy to obtain additional information about indigo, Prussian blue, and ochre pigments. However, it proved unsuitable for detecting other organic dyes due to the excessive intensity of the bulk material absorption. Most attributions of organic colorants were based on visible reflectance spectroscopy results, as we have confidence in the quality of the visible reflectance spectral data and the reference spectra used for comparison. Literature has demonstrated that the technique is reliable as far as a) pure colours are considered and b) when a large set of reference spectral data is collected from mock-up samples dyed with known raw materials (Angelini 2013, Aceto 2014, Maynes-Royas 2017, Gulmini 2013).

Prior to this investigation, we devoted significant time and effort to creating a comprehensive database, including nearly all traditional Japanese dyes and pigments. We carefully evaluated the effect of concentration by replicating 3 to 5 different mock-ups with varying concentrations, and we considered the influence of mixing two dyes or pigments (some plots showing it are available in the supplementary material). Regarding the mordant, we only considered alum, as it is the most frequently cited in the literature. We have added this information within the text, at lines 205-215 of the revised manuscript.

Currently, our compilation of synthetic dyes is limited, but we are expanding it to address wider variability. This is a substantial task because the number of synthetic dyes far exceeds the variability of natural compounds, and it is challenging to obtain samples of early synthetic dyes. We believe that the small yet significant number of these dyes tested is adequate for the present project. To account for this variability, we have revised the text (results and discussion sections) to convey that our analyses are not definitive but rather a prompt for further research in the field. We have also addressed the limitations of visible reflectance analysis at lines 173-190 of the revised manuscript.

Previous studies (see below for example) should also be considered when discussing the results.

We have added some references to studies performed on ukiyo-e prints at lines 160-161 and 537-543 in the revised manuscript.

Page 8, line 281: Please add information on the colorants yamahaji and Hansa yellow (e.g. main coloring component). yamahaji = aqueous extract of Japanese sumac wood? Hansa yellow = synthetic dyestuff containing an azo group?

We clarified the sentence, as follows (lines 306-315 of the revised manuscript):

“Yellow areas give evidence of the use of different dyes, although their identification is considered quite problematic due the similarity of their spectra (Figure 3). In area 59_8, the presence of yamahaji can be proposed, as the spectrum of the sample clearly matches the reference spectrum. Yamahaji is a traditional Japanese dye based on the flavanonol fustin, extracted from the wood of Japanese sumac (Toxicodendron vernicifluum) [12,50]. In sample 69_5, the yellow parts were probably achieved using a synthetic dye from family of arylide, or Hansa, yellow [51]. The second derivative graphs obtained from the spectra of the sample and the reference (Hansa yellow PY3) both show a maximum at 480 nm and a minimum at 510 nm. The slight differences in the reflectance spectrum are attributed to the varying concentrations of the dye on the support [43], as proved by Figure S1.”

Page 11, lines 336-339: Spectral features of cotton reference and differentiation from bast fibers such as hemp, i.e. the absence of ligning signals should be briefly mentioned. Were additional microscopic examinations carried out on the plant fibers?

We added the spectral features of cotton and clarified that no signals from lignin or modified cellulose were found, as explained at lines 372-386 of the revised manuscript. As extensively explained in a previous work from us, FTIR spectroscopy is adept to discriminate among cellulosic fibres (Geminiani et al, 2022). We are confident that the results obtained with ATR-FTIR spectroscopy could be expanded to ER-FTIR spectra, as we are going to fully write down in a further publication. Being our analyses conducted in a non-invasive way, microscopic examination couldn’t be performed.

Page 12, line 360: Were characteristic marker bands for indigo at 1462 and 1482 cm^-1 also detected?

Other characteristic marker bands for indigo are indeed detected at 1462 and 1482 cm^-1, especially when the textile is particularly rich in indigo. They have been marked in Figure 7. However, we decided to focus on the spectral features which are not coinciding with the cellulosic substrate. The revised text can be found at lines 407-412 of the revised manuscript.

 

 

 

Reviewer 2 Report

Comments and Suggestions for Authors

Dear Athours

Dear Authors, I would like to extend my congratulations on your manuscript that sheds light on the traditional Japanese textile dyeing technique. Your meticulous attention to detail in the introduction and discussion, particularly in relation to the technique's implications for data interpretation, is truly commendable. The fusion of technical aspects with data reading is a crucial element in heritage studies, and your manuscript exemplifies this beautifully.

I do not have specific comments but I would like just to point out two minor things:

Figure 2 – please, instead of reporting Offset Y values (here and in the other figures), report the correct unit and add (a.u.) arbitrary unit. In the upper part of the graph, there is a light purple line that does not refer to a specific point. Is it the average among them? Probably 69_2 needs to be in light purple

 

Page 9 line 22  – I appreciate the simulation of the two dyes. It would be interesting to get additional info on the mix, if possible, indicating eventually how much the contribution of one dye respects the other.

Regards

 

Author Response

We thank the reviewer for the positive feedback. He could grasp the meaning of our work and he raised some issues which have been solved improving the overall quality of the paper. In particular, we have revised the graphs as suggested by the reviewer, and added some extra information about the simulation of the mixture of dyes in Section 2.5.

Reviewer 3 Report

Comments and Suggestions for Authors

Feedback Japanese Dyeing paper

I think this is an interesting paper, especially since it reveals quit some contextual information about Japanese dyeing techniques. The paper is clearly written. Although I appreciate the aim to investigate the textiles using non-invasive techniques, the paper clearly misses a critical reflection on this. First of all, if a non-invasive approach is chosen, a multi-analytical approach is certainly needed since one technique can add to the other. The authors mention this themselves (line 160-161), but decided to focus on IR and UV-Vis. Especially XRF us a technique widely available, very fast and relatively easy to apply for the identification of inorganic compounds, such as mordants. A second technique mentioned is Raman, which could be more conclusive with respect to colorant identification, including Prussian blue. Saying this, it could be that especially cellulosic fibres shows strong fluorescence but at least the authors should show that. Secondly, the non-invasive techniques also comes with disadvantages, which should be addressed.

Especially for the colorants, techniques are used which are not conclusive. As example, there are many compounds with similar spectra as Ponceau red 2R. Based on UV-Vis you can state that the dye found belongs to the acid red dye class and likely to the ponceau group, but without either LC-PDA or MS you can not distinguish between them. This is also true for yamahaji which seems to be a sumac extract. Even with a technique as LC and MS, it is impossible to distinguish between different source for sumac, unless there is a specific compound which is likely not the case. Prussian blue cannot be easily identified with UV-Vis or FTIR, it would help to perform XRF for the inorganic elements although Raman would be even better. Regarding madder, the author already indicate that the spectrum is not perfect, that is fine. Rhodamine B might be very well distinguishable via UV/Vis, but it would be good to present the results of other rhodamines as well to show that they really result in different spectrums. Based on this, the identification of most colorants are not conclusive, so the paper can not be accepted in this way. Either provide additional data (of closely related compounds using the same technique, or with complementary techniques) or, if that is not feasible, the conclusions should be adjusted stating that the results are indicative at best. In that case, the paper is weakened.

In the conclusion, a much more critical reflection on the techniques is required. It is obviously an advantage that these techniques can be applied non-invasively, which should not be underestimated. But due to the lack of separation of the colorants, it is not very conclusive. But sometimes knowing a dye class, instead of the specific dye molecule, is already a sufficient answer, for example if you like to know if synthetic or natural dyes are present and how objects are created and maybe treated.

Some specific comments:

Is Prussian blue really so unexpected (line 447)? It is known as the only inorganic colorant able to dye textiles. And is Prussian blue really used to paint, so using a binding medium (line 536)? If so, binding medium should be identified as well. If not, it could have been used to dye.

Line 281: Provide the botanical name for yamahaiji and describe what kind of compounds are present.

Line 223: here it is stated that sampling is done with ER-FTIR, I think the authors mean analysis since no samples were taken.

Note: in several occasions abbreviation are introduced without proper explanation, I could not find a list of abbreviations (maybe I missed it), but otherwise it is custom the first write the full name with abbreviation between brackets, afterward the abbreviation can be used (unless you have a header / title of a section).

Author Response

We thank the reviewer for the feedback and for the appreciation. The owner of the collection did not grant us permission to take any samples from the objects under study, so the use of HPLC-MS was not considered. Conversely, the application of portable Raman spectroscopy or XRF could have provided complementary information, but these techniques were not available at the time of the analyses. As highlighted by much of the available literature, FORS or visible reflectance spectroscopy should be viewed as preliminary techniques, with results strengthened by other complementary portable or minimally invasive methods (all references cited in the text: Mounier 2018, Cesaratto 2018, Tamburini 2019, Tamburini 2020, Vermeulen 2020).

In this study, we used FTIR spectroscopy to obtain additional information about indigo, Prussian blue, and ochre pigments. We are confident that the identification of Prussian blue is reliable, as ER-FTIR spectroscopy has proven to be extremely sensitive to this compound, both in our experience (Rampazzi et al, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 176 (2017) 142–154; Rampazzi et al, Microchemical Journal 157 (2020) 105017) and in other works (Vetter et al, e-Preserv. Sci. 8 (2011) 10–22; Biron et al, Color Res Appl. (2020) 45: 262–274). However, it proved unsuitable for detecting other organic dyes due to the excessive intensity of the bulk material absorption. Most attributions of organic colorants were based on visible reflectance spectroscopy results, as we have confidence in the quality of the visible reflectance spectral data and the reference spectra used for comparison. Literature has demonstrated that the technique is reliable as far as a) pure colours are considered and b) when a large set of reference spectral data is collected from mock-up samples dyed with known raw materials (lines 181-185 of the revised manuscript). We have also addressed the limitations of visible reflectance analysis at lines 186-190 of the revised manuscript. Prior to this investigation, we devoted significant time and effort to creating a comprehensive database, including nearly all traditional Japanese dyes and pigments. We carefully evaluated the effect of concentration by replicating 3 to 5 different mock-ups with varying concentrations, and we considered the influence of mixing two dyes or pigments (some plots showing it are available in the supplementary material). Regarding the mordant, we only considered alum, as it is the most frequently cited in the literature. We have added this information within the text, at lines 205-215 of the revised manuscript.

Currently, our compilation of synthetic dyes is limited, but we are expanding it to address wider variability. This is a substantial task because the number of synthetic dyes far exceeds the variability of natural compounds, and it is challenging to obtain samples of early synthetic dyes. To account for this variability, we have revised the text to convey the notion that our analyses are not definitive but rather a prompt for further research in the field. The reviewer can find the revised text within results and discussion sections, highlighted in red.

As for the specific points raised by the reviewer, our answers follow.

Is Prussian blue really so unexpected (line 447)? It is known as the only inorganic colorant able to dye textiles. And is Prussian blue really used to paint, so using a binding medium (line 536)? If so, binding medium should be identified as well. If not, it could have been used to dye.

The identification of Prussian blue is unexpected because in a textile dyed with aizome technique the different shades of blue are assumed to have been obtained by dipping the textile a different number of times in the dye bath. As a pigment, its use is not surprising as there are both historical sources and scientific studies attesting its presence in Japan since the beginning of 19^th century or even before. On the contrary, its use as dye it is not attested in Japan. In some objects it has been identified together with glue, but not in all the tested areas. The text has been clarified at lines 500-508 of the revised manuscript. Table 1 summarizes our findings. Due to the limitations of the non-invasive approach, it is not possible to deepen the issue.

Line 281: Provide the botanical name for yamahaiji and describe what kind of compounds are present.

We clarified the sentence, as follows (lines 312-313 of the revised manuscript):

“Yamahaji is a traditional Japanese dye based on the flavanonol fustin, extracted from the wood of Japanese sumac (Toxicodendron vernicifluum) [12,51].”

Line 223: here it is stated that sampling is done with ER-FTIR, I think the authors mean analysis since no samples were taken.

We clarified the sentence, as follows (lines 243-245 of the revised manuscript):

“Analyses were conducted using both techniques in the same area whenever possible. However, there were instances where collecting ER-FTIR spectra was not feasible due to limitations in the maximum height accessible to the instrument.”

Note: in several occasions abbreviation are introduced without proper explanation, I could not find a list of abbreviations (maybe I missed it), but otherwise it is custom the first write the full name with abbreviation between brackets, afterward the abbreviation can be used (unless you have a header / title of a section).

The reviewer is obviously right. We have revised the text accordingly.

 

 

Round 2

Reviewer 3 Report

Comments and Suggestions for Authors

I think the authors improved the paper well, following my previous comments. The paper can be published

Author Response

We thank the reviewer for the words of appreciation.