Investigations of Feldspar-Quartz Raw Materials After Firing: Effect of Various Na₂O/K₂O Ratio and Synthetic Pigments Addition

Round 1

Reviewer 1 Report

This revised version of the manuscript is a significant improvement and addresses the previous comments of this reviewer, resulting in a nice paper with interesting new results and a novel approach to colour of ceramics that should be of wide interest to reader of this journal. The only changes still required are to the formatting of the references, several of them do not have subscripts in chemical formulae in the article titles, e.g. refs 8, 18, 22, 31 and others. Once this is done the paper should proceed to publication

Author Response

Response to Reviewer 1 Comments

Point 1: The only changes still required are to the formatting of the references, several of them do not have subscripts in chemical formulae in the article titles, e.g. refs 8, 18, 22, 31 and others.

Response 1: Formatting of the references, i.e. subscripts and superscripts in chemical formulae and some other deficiencies in the article titles have been changed/corrected in the following refs: 8, 18, 22, 31, 32, 33, 34, 45, 50, 51. The changes have been highlighted using “Track changes” function in Microsoft Word (see attached file).

The Authors wish to kindly thank the Reviewer for his/her support that encouraged us to significantly improve and re-submit the article.

Author Response File: Author Response.pdf

Reviewer 2 Report

The authors have added the optical absorbance spectra as measured by the total reflectance of their samples. They have thoroughly discussed these spectra based on the literature. All the text relating with the topic of colour has been improved and is clear.

In the abstract, please correct "d-d charge transfer transitions" by "d-d transitions" (line 27)

In the experimental part, please comment about the obtention of absorbance spectra from reflectance spectra. From the reflectance spectra, the Kubelka-Munk transformation allows to obtain the F(R) which is analogous, but not exactly the same, as absorbance. Please complete to be more rigorous on this point and correct the y-axis label on your spectra if necessary ("absorbance%" seems odd).

Author Response

Response to Reviewer 2 Comments

Point 1: In the abstract, please correct "d-d charge transfer transitions" by "d-d transitions" (line 27).

Response 1: The adjustment has been made and now the proper term “d-d transitions’ is used (line 27)

Point 2: In the experimental part, please comment about the obtention of absorbance spectra from reflectance spectra. From the reflectance spectra, the Kubelka-Munk transformation allows to obtain the F(R) which is analogous, but not exactly the same, as absorbance. Please complete to be more rigorous on this point and correct the y-axis label on your spectra if necessary ("absorbance%" seems odd).

Response 2: Of course, the measured parameter was the reflectance (R) and it was converted into the absorbance (A). To make such a transformation, it is necessary to know the transmittance (T) of the sample, since A+R+T=1. However, for opaque objects or if the thickness of the sample (d) is much higher than the wavelength (λ), i.e. d >> λ, as in this case (the thickness of the samples was d≈10 mm whereas wavelength was λ=220-2200 nm), the transmittance is equal to 0 and therefore A+R=1.

To clarify any doubts concerning measured optical spectra, the following comment has been added to the Materials and Methods section (lines 115-118): ‘The measured parameter was the reflectance (scale 0-100%), which was converted into the absorbance and analyzed. Such a calculation was feasible because the samples thickness was incomparably greater than the wavelength of the light used (10 mm vs. 220-2200 nm).’ See also the attached file.

As the reflectance is expressed as a percentage and consequently the absorbance is also expressed as a percentage, the y-axis description in Figure 7 has remained unchanged.

 

The authors wish to thank the Reviewer for the constructive comments and suggestions that help to improve the article significantly.

 

Author Response File: Author Response.pdf

This manuscript is a resubmission of an earlier submission. The following is a list of the peer review reports and author responses from that submission.

Round 1

Reviewer 1 Report

This is a well-written and novel study of colour effects in feldspars through additions of Fe2O3 and TiO2. The authors present a balanced and well-researched case, and overall the study is worthy of publication. A few minor changes are required prior to publication, as follows:

 

• Table 1. State whether weight or mol %
• Explain calibration and uncertainties on XRF analyses.
• Explain assumption that recoil-free fraction Fe2+/Fe3+ obtained from Mossbauer spectroscopy affects redox ratio obtained from spectral areas, with referencing.
• Table 2 caption. Analysed weight % composition....
• Explain firing cycle of samples in more detail, e.g. ramp rate, holding time, cooling rate, so a full thermal profile is shown.
• Explain pellet-pressing procedure and sample sizes.

 

Reviewer 2 Report

The article deals with the origin of color in ceramics materials obtained by firing raw feldspar-quartz minerals and additional iron and/or titanium oxides. The context is the importance of controlling the color stability of ceramics tiles. However, one question I have here is : ceramics tiles are not made only of the raw feldspar-quartz of this study, other raw materials are added (clays, carbonates...). The color results from the transformation of the whole phase system and I am not sure about the relevance of studying the color in one component sub-system only.

I find the study well presented and argumented regarding the transformations of the raw material to ceramics, thanks to the XRD work and the convincing discussion with respect to the relative K2O and Na2O content. However, I find that the other theme of the study, the color, is not properly experimentally supported and argumented. Many inferences about the speciations of coloring ions are made only on the basis of the colour coordinates... First, color coordinates are not sufficient to trace back the speciation, and second it should be the reverse! From proper characterization of the speciation, infer an understanding of the color coordinates. So there is a fundamental problem, I find, with the structure of the demonstration.

The only speciation data about the colouring ions are the Mössbauer spectra for Fe. There is nothing for Ti. The crystalline phases Fe2TiO5 and FeTi2O5 that are suggested as an origin of the darkening of the color are not detected by XRD (below detection limit presumably) and nothing proves that they indeed exist. The existence of intervalence charge transfer between Fe2+ and Ti4+ is also a (more convincing) hypothesis for the darkening of the materials bearing the two oxides (Fe and Ti), but there are no UV/Vis absorbance spectra to demonstrate it. A demonstration would be to follow the temperature dependency of the absorbance spectrum, because intervalence charge transfer varies with temperature (as in a study of Galoisy et al about the dark color of obsidians). Moreover, the text is not clear about the different optical absorption phenomena, I raised many unclear and confusing sentences. These more specific comments are in the joint file.

Therefore I would not recommend plublication, without major changes with the reduction of the discussion about color, OR if color remains an important theme, the supply of absorption spectra, if possible with complementary data (XANES of Ti K edge or Fe K or L edge), to support the discussion about color.

 

Comments for author File: Comments.pdf