Colour Homogenisation and Photostability of Beech Wood (Fagus sylvatica L.) as Affected by Mild Steaming and Light-Induced Natural Ageing

Comments 1: In the abstract (line 17), the authors state that the CIELab system includes the parameters LabCh. This is incorrect. The CIELab system consists only of the parameters L, a, and b, whereas C (chroma) and h° (hue angle) belong to the alternative CIELCh system. Although the authors mention the CIELab system, they also describe C and h values, which are not part of it. An explanation of the CIELCh system should be included in the methods section.

Response 1: Thank you for your valuable comment. You are correct that the CIELAB system formally includes only the parameters L*, a*, and b*. However, we would like to clarify that the colorimeter used in this study directly provided values for chroma (C*) and hue angle (h°), in addition to the standard CIELAB values. Although these derived parameters are typically associated with the cylindrical representation of color — the CIELCh color space — we used all of them as part of our evaluation to gain a more comprehensive view of color changes. To address this point, we have corrected the terminology in the abstract and clarified the distinction and relevance of both CIELAB and CIELCh in the Methods section.

Comments 2: In the materials section, there is no specific description of the material preparation process. Only citation 18 is provided. However, readers may not have access to all references, and the manuscript should offer sufficient detail to allow the tests to be reliably reproduced. Many factors affect wood color and its change, beginning with the growth site, felling season, initial drying conditions, temperature, and duration of processing. All of this information is currently missing and is essential for accurately interpreting the results and the observed color changes after aging.

Response 2: We appreciate the reviewer’s observation regarding the insufficient detail provided for the material preparation process. While citation [18] outlines the general procedure, we recognize the importance of making this manuscript fully self-contained to ensure reproducibility. We have now expanded the Materials section to include all relevant details.

Comments 3: In the introduction (line 40), the authors note that UV light is primarily responsible for color changes. However, it is well known that standard window glass blocks most UV radiation. Can the authors provide a more precise characterization of the radiation levels received by the samples during the 35-day aging period, possibly including numerical values?

Response 3: Thank you for this relevant observation. We fully agree that standard window glass significantly reduces the amount of ultraviolet radiation that reaches indoor surfaces. Unfortunately, during the 35-day indoor aging period, we were t unable to record the exact radiation intensity or spectrum received by the samples.

Nevertheless, the samples were exposed under natural indoor conditions, placed near a south-facing window in a location that receives regular daylight. Although most UV-B and UV-C components are effectively blocked by the window glass, a portion of UVA radiation and visible light does penetrate and contribute to surface colour changes over time. The observed changes thus reflect real-life conditions typical for indoor wood surfaces, which was the aim of our study. We have clarified this limitation and context in the manuscript.

Comments 4: In section 2.4 (ATR-FTIR), the authors describe the device and method used, but do not include any information on sample preparation (e.g., size, pretreatment, handling procedures, or the number of specimens). This information is critical for reproducibility.

Response 4: Experimental samples were used for infrared analysis without further preparation, because the ATR technique does not require further treatment for the analysis of smooth surfaces of solid samples. I have added a description of the spectrum evaluation procedure.

Comments 5: In the results, discussion, and conclusions, the authors claim that the color of steamed wood is more stable. While it is true that steamed wood experienced less color change than untreated wood, it is important to acknowledge that steaming itself alters the wood’s initial color. Moreover, based on Figure 1 and Table 2, the final color of aged steamed and natural wood is nearly identical. This raises the question of whether the steaming process is necessary, especially considering its potential cost implications.

Response 5: Agree. We have updated text in the manuscript.

Comments 6: Finally, the conclusions could be more specific and clearly supported by the study's findings. As written, they remain overly general.

Response 6: Agree. We have updated text in the manuscript.

Comments 1: The Introduction section is too general. For instance, in lines 46–53, the references to “quantitative methods” and “properties” are vague. Clarify what properties are being measured and how environmental or wood-specific factors influence color. The role of extractives in color change is mentioned but insufficiently explained—especially whether this is exclusive to tropical species. Incorporating and discussing prior relevant research would provide a better theoretical framework.

Response 1: Thank you for the comment. The paragraph (lines 46–53) has been reworded to provide a clearer and more focused theoretical background.

Comments 2: Section 2.1 lacks critical information about the origin of the beech wood samples and the specific instruments used for steaming and conditioning. For reproducibility, please include the manufacturer and city for all equipment.

Response 2: Thank you for your observation. A similar comment was made by another reviewer, and we fully agree on the importance of providing sufficient detail for reproducibility. We have now added information about the origin of the beech wood samples, including the location, as well as detailed descriptions of the steaming and conditioning process. The manufacturer and city of all instruments used for steaming, conditioning have also been specified. These additions are now included in Section 2.1 of the revised manuscript.

Comments 3: Section 2.2 would benefit from a schematic drawing or photo of the ageing exposure setup. Additionally, more location-specific information (e.g., GPS coordinates, site orientation, shading, solar radiation, sunshine hours) would provide a more comprehensive context for the ageing conditions.

Response 3: Agree. We have updated text in the manuscript.

Comments 4: Line 91: Define abbreviations (h° for hue angle, C* for chroma) at their first mention. Use consistent notation throughout (h or H), including in captions and summary sections.

Response 4: Agree. We have, revised it (section 3.2).

Comments 5: Statistical evaluation would support the findings of this article greatly. Please indicate which differences in values are statistically significant.

Response 5: Thank you for your valuable comment. We have now supplemented the manuscript with comprehensive statistical analyses, including means, standard deviations, and three-way ANOVA results. The statistical evaluation highlights which differences between treatments, tissue types, and ageing times are significant. All statistically significant effects and interaction terms are clearly indicated in the revised results and discussion sections to support and strengthen the findings of this study.

Comments 6: Figure 1 is not cited in the main text; this should be corrected. Please correct “Falshe heart”  sign.

Response 6: Agree. We have, modified it.

Comments 7: Consider presenting some results in diagrams rather than tables for greater clarity.

Response 7: Thank you for your suggestion regarding the presentation of results. While we agree that diagrams can enhance clarity, we believe that including additional figures at this stage might lead to duplication of data already clearly presented in the tables. Due to time and resource constraints, we have therefore focused on ensuring that the tables are well-organized and thoroughly explained. We will consider incorporating more visual representations in future studies to improve clarity further.

Comments 8: Including the ΔE* values in the results table would help quantify color differences and indicate whether they are perceptible to the human eye. Specify the threshold above which changes are considered significant or visible.

Response 8: Thank you for your valuable suggestion. We have now included the ΔE* values in the results table to better quantify the colour differences observed. This information has been incorporated into the results section to clarify the practical significance of the colour changes.

Comments 9: Quantify described results—e.g., provide numerical differences or percentage changes rather than generalized statements.

Response 9:

Comments 10: Figure 3: The spectra should be vertically offset to avoid overlapping. Use superscript for “-1” in cm⁻¹. Consider adding dashed lines to mark key absorption peaks. Please cite the references in which these absorption bands were identified.

Response 10: The figures were edited and the required data was added.

Comments 11: Notation text in the captions of Figures 3–5 should be reduced in size and consistently applied across all figures. Add missing legend/notation text where applicable.

Response 11: The text in the captions was corrected.

Comments 12: Line 223 contains a typo: “skelet” should be corrected.

Response 12: It was corrected.

Comments 13: Include more detail on the chemical and structural differences between mature wood and false heartwood and how this affects the treatment outcomes.

Response 13: Thank you for your valuable suggestion. This information has been incorporated into the discussion section.

Comments 14 It should be clearly stated that steaming does not improve the biological durability of wood (e.g., resistance to fungi or insects).

Response 14: Agree. We also acknowledge that steaming primarily improves the colour stability and visual appearance of beech wood but does not enhance its biological durability, such as resistance to fungi or insects.

Comments 15: This manuscript provides new, practically useful data on beech wood color, photostability and steaming.

Response 15: Thank you for recognizing the practical relevance of our study. We are pleased that the manuscript contributes valuable new data on the colour characteristics, photostability, and effects of steaming on beech wood.