Temperature Assessment Through Decal Color in Microwave-Fired Porcelain

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

This research presents a method to evaluate microwave firing temperature using color analysis, which is innovative and has potential for application. However, this paper has some problems and needs to be revised to improve its quality and academic value.

1. The abstract is concise but would benefit from more detailed quantitative data and specific findings to provide a clearer overview of the study's contributions and significance.
2. The use of "approximately four samples per test" raises concerns about statistical validity. Include error bars, standard deviations, or ANOVA results to confirm consistency.
3. Figure 8-9 Measurement conditions (e.g., light, observer angle) should be clearly stated. Tables 1–3 are fragmented and difficult to interpret. Consolidating temperature data into a single, structured table would improve readability.
4. The study focuses on low-fire blue and silver decals. The generalizability of the method to other pigments or complex multi-color decorations is unclear. A discussion of pigment-specific thermal sensitivity and calibration requirements is needed.

The research data of the article is detailed, but it needs to be further improved in terms of theoretical discussion, data analysis, and literature comparison in order to improve the persuasiveness of the research conclusions.

Author Response

Reviewer comments and suggestions are presented in black, while author responses are provided in blue.

 

First of all, the authors would like to sincerely thank the Reviewer for their thorough evaluation and constructive comments. The authors truly appreciate the time and effort dedicated to reviewing the manuscript and have carefully considered each point raised.

This research presents a method to evaluate microwave firing temperature using color analysis, which is innovative and has potential for application. However, this paper has some problems and needs to be revised to improve its quality and academic value.

Authors Response:
To address the concerns raised by the Reviewer, we would like to emphasize that several aspects of the manuscript were revised and improved. In addition to the specific points outlined below, we have also revised the Introduction to incorporate more focused and relevant literature, particularly related to pigments. Despite this effort, we found it challenging to find detailed and specific scientific references concerning the thermal behavior of decorative pigments. As now stated in Page 3 Lines 93-100 of the Revised manuscript “Although decorative pigments are extensively used in ceramic applications, there is a notable lack of scientific literature addressing their specific thermal behavior regarding color stability and firing calibration. This information is often considered a trade secret by manufacturers, as is the case with other confidential data historically associated with ceramic production [9,10]. Furthermore, by quoting [10] ‘Why cannot ceramists get all the data they need … many datasets are available online, but are distributed in a difficult-to-navigate maze of unconnected databases, in many different formats, using nonstandard terminology.’.”

Regarding the research design and methodology, we share the perspective of Reviewer #2 and did not introduce substantial modifications, as we are confident that both are appropriate and sufficiently described. Where relevant, we also acknowledge limitations and point to potential future improvements.

Regarding the presentation of results and the conclusion, we believe that the revisions made have significantly enhanced the clarity and quality of the manuscript. In particular, the improvements to Figures 8 and 9 contribute to a more intuitive understanding of the key findings. These changes also support the article’s main conclusions more effectively. An additional results analysis is presented, Page 14, Lines 398-431 of the revised manuscript, improving both results and Conclusions.

Concerning the quality of English, we acknowledge that we are not native speakers. To ensure clarity and correctness, we utilized IA language assistance tools, as mentioned during submission via the JMMP platform. We agree with another Reviewer that stated: “The English is good and requires no improvement.” While the manuscript may not be flawless in its language use, we believe that it is clear and easily comprehensible. The objectives, rationale, and significance of the study, particularly regarding the challenges of temperature assessment in microwave-fired materials, are effectively communicated throughout the text.

Additional language revisions were made during the resubmission process to further improve readability.

All modifications made to the manuscript are clearly marked using the Track Changes tool.

 

Additional issues raised by the Reviewer#1 are addressed in detail in the responses that follow.

1. The abstract is concise but would benefit from more detailed quantitative data and specific findings to provide a clearer overview of the study's contributions and significance.

Authors Response:
We appreciate the Reviewer's comment and have carefully considered it. If we understand the suggestion correctly, providing more detailed quantitative data would require conducting additional tests with a statistically more representative number of samples, including variations with other decals, pigments, and colors. As these fall outside the scope of the present study, and considering that the current abstract already summarizes the key findings and addresses the main issues investigated, we did not make significant changes to it. Nonetheless, we remain open to further adjustments should the Reviewer consider them essential. 

2. The use of "approximately four samples per test" raises concerns about statistical validity. Include error bars, standard deviations, or ANOVA results to confirm consistency.

Authors Response:
We appreciate the Reviewer’s valuable comment. This has been graphically corrected, with the inclusion of error bars in both Figures 8 and 9, and in this way providing a clearer representation of data variability. Additionally, a new Figure 9b has been included to present an overall view of the ab coordinates pairs, offering a broader context. The updated Figures 9c and 9d (previously Figures 9b and 9c) now serve as zoomed-in views of the specific areas of interest highlighted in the new Figure 9b. These modifications aim to improve the clarity and consistency of the data presentation. 

3. Figure 8-9 Measurement conditions (e.g., light, observer angle) should be clearly stated. Tables 1–3 are fragmented and difficult to interpret. Consolidating temperature data into a single, structured table would improve readability.

Authors Response:
This point is divided into two parts.

Regarding Figures 8 and 9:
The requested measurement conditions have been clarified in the manuscript (Page 7, Lines 305-307), where the following sentence was added:
“The color coordinate measurements were performed under daylight illuminant (D65) and 10° standard observer angle, using a Konica Minolta CM-700D spectrophotometer equipped with an ∅8 mm target mask.”

Regarding Tables 1–3:
We maintained the table structure for the following reasons:

• Table 1 presents PTCR’s temperature measurements at different positions inside the microwave furnace.
  
  
• Table 2, although complementary to Table 1, presents a distinct data set. Combining Tables 1 and 2 would result in a less readable table, due to the required reduction in font size, which would also conflict with the journal’s formatting guidelines.
  
  
• Table 3 displays temperature measurements from/in the electric and industrial furnaces/kilns. These datasets refer to different types of equipment, not related to microwave, and we believe that keeping them as separate tables enhances clarity and readability.

For these reasons, we have opted to retain the current structure. However, as a correction, in Table 3, the label “TP” was changed to “TT” to more accurately reflect the use of thermocouples rather than pyrometers in the electric and industrial furnaces/kilns. The abbreviations “TP” and “TT” have been clarified and added to the list of abbreviations at the end of the manuscript.

4. The study focuses on low-fire blue and silver decals. The generalizability of the method to other pigments or complex multi-color decorations is unclear. A discussion of pigment-specific thermal sensitivity and calibration requirements is needed.

Author’s Response:
We thank the Reviewer for this pertinent observation, which we address in two parts:

1. Generalizability to Other Pigments and Multi-Color Decorations:

The study does not intend to generalize the findings to all pigment types or complex multi-color decorations. After reviewing the manuscript, we believe it is clear that no such generalization is made.

What we say is that regarding multi-color decals, as the examples in Figure 10 show, and as mentioned in Page 20 Lines 626-628, “... research indicates that microwave-fired decorated porcelain can match the quality of conventionally fired pieces in a faster and less demanding energy heat work.”. Moreover, we acknowledge potential limitations and variability, particularly with multi-color decals. This is one of the reasons why we say on the Page 2 Line 81 that “Multi-color decorations may require multiple decoration firing stages.”. Nevertheless, nowadays, some commercially available decals are designed for single firing, as is the case for those used and presented in Figure 10.

2. Pigment-Specific Thermal Sensitivity and Calibration Requirements:

This is an important and complex topic. We revisited the literature to identify relevant studies on the thermal behavior and sensitivity of decorative pigments. Unfortunately, as noted in the revised manuscript (Page 3 Lines 93-103) “Although decorative pigments are extensively used in ceramic applications, there is a notable lack of scientific literature addressing their specific thermal behavior regarding color stability and firing calibration. This information is often considered a trade secret by manufacturers, as is the case with other confidential data historically associated with ceramic production [9,10]. Furthermore, by quoting [10] ‘Why cannot ceramists get all the data they need … many datasets are available online, but are distributed in a difficult-to-navigate maze of unconnected databases, in many different formats, using nonstandard terminology.’. 

In a kind of review article [9] it is confirmed that different pigments and colors require distinct “maturation” temperatures, which are further affected by the specific manufacturing techniques used in pigment preparation [9,11].“.

While a detailed analysis of pigment-specific sensitivity and calibration would undoubtedly enrich the study, it falls beyond the scope of this work. As highlighted in the Conclusions section (Page 19, Lines 611–612), “Present research focuses on the microwave firing of decorated porcelain, aiming to achieve the same aesthetic results as in conventional kilns.” Likewise, in the Discussion (Page 17, Lines 515–518) notes that “Since some colors change with temperature, these transformations have been used as indicators to assess the effectiveness of microwave processing. Analysis of L*, a*, and b* color coordinates have shown that microwave-fired samples exhibit differences in color tone compared to their electrically-fired counterparts.”

This work should be seen as a proof-of-concept case study that arose from an opportunity not initially foreseen. Upon observing significant color and brightness shifts, particularly a pronounced red-to-gray transformation, we expanded the investigation to evaluate whether this effect could serve as an indicator of the thermal energy applied during microwave firing.

We must also emphasize that this research was conducted without dedicated funding:
"This research received no specific grant from any funding agency in the public, commercial, or not-for-profit sectors."
Consequently, we currently lack the financial and logistical resources to extend this study further to include pigment-specific sensitivity analyses, or others.

Nonetheless, we believe the present findings lay a solid foundation for future work and introduce a novel direction in the assessment of thermal treatment effectiveness in ceramics. As stated in the revised manuscript (Page 19, Lines 594-604), ”Although some issues require further refinement, the present study provides strong evidence that the color change of a pigment can be used to assess the firing temperature or the thermal energy to which a ceramic piece has been exposed (the heat work). Furthermore, the study suggests that, particularly when using pigments with high firing temperature sensitivity, especially near a known temperature, this method could be used to map the temperature distribution across the entire surface of the piece. This would enable the creation of a 3D thermal map through post-firing analysis. While real-time 3D in situ monitoring is not practically feasible, this approach offers a valuable tool for assessing thermal homogeneity inside a microwave furnace, mapping it, and aiding process optimization and kiln design improvements, albeit reactively, that is, post-firing.”.

We hope this clarifies our approach and the limitations of generalization and pigment-specific analysis in the current work.

The research data of the article is detailed, but it needs to be further improved in terms of theoretical discussion, data analysis, and literature comparison in order to improve the persuasiveness of the research conclusions.

Author's Response: We appreciate the Reviewer’s comments and acknowledge the importance of strengthening the theoretical framework and contextualizing our findings through comparison with the existing literature. In that sense, some extra references were added to the revised manuscript. One of those additions is found in Page 3, Lines 111-117: “As referred in [13], ‘Any variation from the desired temperature and atmosphere of the kiln can alter the color that develops during the firing process.’ Another study [14] highlights the influence of firing conditions on color tonality in beige and dark brown glazes for tile applications. The results demonstrate that the samples are sensitive to firing parameters, with the beige pigment showing greater sensitivity to variations in temperature and soaking time”. And in Page 5, Lines 223-227: “Microwave heating has also shown clear advantages in pigment sintering and synthesis, offering more efficient and environmentally friendly processes compared to conventional ones [46,47]. The pigment temperature-complex permittivity dependency [46], particularly the loss factor, is crucial when applying microwave firing in decorated ceramics”.

Many of the concerns raised at this point have already been addressed in the responses above. Nevertheless, we would like to reiterate and clarify the following:

Regarding pigment behavior and color sensitivity, this is certainly a topic of interest to the ceramics research community and would benefit from further open-access investigation. We consider that an in-depth study of this aspect, although valuable, lies beyond the main focus of the current work.

As well, the observed shift in the ab* pair data curve in Figure 8, particularly the increase in a* values above approximately 1000°C, is indeed intriguing and potentially relevant. This consideration also applies to the data shown in Figure 9. However, understanding the underlying cause of this shift would require additional targeted experiments and a broader set of data. In our view, such an investigation, although worthwhile, would risk diverting the focus of the paper away from its central goal: assessing the feasibility and effectiveness of microwave firing as an alternative to conventional ceramic decoration firing methods, and the use of decorated ceramics for the firing temperature evaluation and even surface temperature mapping.

While we recognize the value of expanding the theoretical discussion and conducting more exhaustive literature comparisons, we encountered significant limitations in available scientific references addressing the specific thermal behavior of decorative ceramic pigments. As previously noted, such information is often proprietary and not widely documented. Should the Reviewer be aware of relevant literature that addresses these points, we would be very grateful to receive those references for further study and incorporation in future work.

Moreover, as referred in Page 14, Lines 424-426 of the revised manuscript, and only referring to the last part of the added text, “...Although these inflection points are visible, a deeper investigation into their underlying causes lies beyond the scope of the present study. Therefore, we limited ourselves to reporting and highlighting these experimental observations.”.

In summary, we believe that although these discussions would enhance the scope and depth of the study, they are best addressed in follow-up research focused specifically on pigment behavior and thermal calibration. As such, we respectfully consider these beyond the scope of the present work.

Furthermore, concerning the article size, mainly with its emphasis on porcelain references and details, while we have shortened some of the content as recommended by another Reviewer, to satisfy both recommendations, certain parts of the porcelain-related content were removed. However, additional content was included to highlight the current gap in the literature and to justify the relevance of the present research. Even if some of this added content does not introduce highly detailed data, it is intended to clarify the difficulty of accessing comparable studies, particularly regarding pigment behavior in ceramics firing.

Reviewer 2 Report

Comments and Suggestions for Authors

Dear Authors

1. p6v46 Please shorten the description of the CIE Lab system. I suggest deleting some part about porcelain in the introduction - it is too long
2. p3v100 lack of subscripts
3. Figs 8 and 9, please add a description of Fig. between 8 and 9, because it is difficult to understand what it is
4. results about colour, I suggest adding some calculations that can show the difference between colours, e.g. delta E

Author Response

Reviewer comments and suggestions are presented in black, while author responses are provided in blue.

 

First of all, the authors would like to sincerely thank the Reviewer for their thorough evaluation and constructive comments. The authors truly appreciate the time and effort dedicated to reviewing the manuscript and have carefully considered each point raised.

1. p6v46 Please shorten the description of the CIE Lab system. I suggest deleting some part about porcelain in the introduction - it is too long

Authors Response:
This point can be divided into two parts, and both were addressed in the revised manuscript.

First, we appreciate the Reviewer's comment and have carefully considered it. Regarding the suggestion to shorten the description of the CIE Lab system, the corresponding section was reviewed and condensed to ensure that only the most essential information remained, making the content more concise and focused on its relevance to the study.

With respect to the length of the Introduction and its emphasis on porcelain, while we have shortened some of the content as recommended, we also took into account the comments from Reviewer #1, who indicated the need to improve the theoretical discussion, data analysis, and comparison with existing literature. To satisfy both recommendations, certain parts of the porcelain-related content were removed. However, additional content was included to highlight the current gap in the literature and to justify the relevance of the reported research. Even if some of this added content does not introduce highly detailed data, it is intended to clarify the difficulty of accessing comparable studies, particularly regarding pigment behavior in ceramic firing.

To illustrate this point, we included the following statement in the revised manuscript (Page 3 Lines 93-100): “Although decorative pigments are extensively used in ceramic applications, there is a notable lack of scientific literature addressing their specific thermal behavior regarding color stability and firing calibration. This information is often considered a trade secret by manufacturers, as is the case with other confidential data historically associated with ceramic production [9,10]. Furthermore, quoting [10] ‘Why cannot ceramists get all the data they need … many datasets are available online, but are distributed in a difficult-to-navigate maze of unconnected databases, in many different formats, using nonstandard terminology.’.“

2.p3v100 lack of subscripts

Authors Response:
Thank you for pointing this out. The issue regarding the missing subscripts has been addressed in the revised manuscript Page 3, Line 127.

3. Figs 8 and 9, please add a description of Fig. between 8 and 9, because it is difficult to understand what it is

Authors Response:
This issue has been addressed in the revised manuscript on Page 12, Line 384, where we added the following clarification: “Figure 9 presents the color coordinates of the low-fire silver-stamped decal samples fired between 800 °C and 1400 °C in the microwave and electric furnaces, as well as those of the gas-fired references, including dE* color difference relative to reference samples color.“.

Additionally, we believe that the overall revisions made to the results section have significantly improved the clarity and readability of the manuscript. The presentation of data, particularly in Figures 8 and 9, is now more intuitive and accessible to readers, better supporting the interpretation of the article's main findings.

4. results about colour, I suggest adding some calculations that can show the difference between colours, e.g. delta E

Authors Response:
This issue was addressed, with new Figures added to Figure 8 and 9, Page 11, Line 378 and Page 13, Line 390. The text “Regarding the total color difference (dE*) analysis for each case and its reference set, it is worth highlighting the consistency with previous color coordinate discussions. dE* values approaching zero near the temperatures of the reference samples. For silver-colored samples, dE* is lowest at 1000 °C in electric-fired samples showing a better match to Ref.1100 °C than the microwave-fired counterpart at the same temperature.” was introduced in the revised manuscript, Page 14, Lines 427-431, complementing the text introduced above that (Page 14, Lines 398-426).