User Preferences on the Application of Wooden Wall Coverings in Interiors Made of Oak Veneer Residue

Abstract

Guided by the principles of visual perception and basic design, this research was conducted to examine users’ preferences on how they perceive natural unique wood phenomena of Pedunculate Slavonian Oak veneers (Quercus robur L.) such as color changes, wood rays, sapwood, and knots, which in the production and technical sense represent defects and wood residue, but could be used in the design of sustainable and ecological wall decorations. The goal was to detect samples with the most positive attributes and to observe their connection with activities and functional space if they are viewed as wall coverings in the interior. The results confirm that discoloration and wood rays are considered the most harmonious (“prettiest”) decors. Discoloration is associated with quiet cognitive or medium-intensity activity that can be used in libraries, hotel rooms, and classrooms. Wood rays are connected with very quiet activity in ambulance waiting rooms or religious buildings and museums. Knot decors are considered the most natural and are recommended for interiors with very or medium-intensive activities such as restaurants, cafes, and hotel receptions, but attention should be paid to the way the wall decors are arranged on the walls. Sapwood–hardwood decors are the subject of further research and improvement concerning the relationship between the dark and light parts of the veneer. In conclusion, the results provide useful guidelines for manufacturers with a large veneer residue in production and who want to design decorative wall panels, as well as for designers and architects designing interiors for a specific purpose and function where certain user behavior and psychological stimulation are desired.

1. Introduction

Historically, wood has always been used as a traditional material in construction, furniture making, and interior decoration [1]. In traditional wooden houses, the walls were made of massive, often rough-hewn boards, so the structure of the wood remained visible even from the “inside” [2]. Today, we see this phenomenon as a desirable effort to preserve naturalness in interiors.

The desire to return wood to interiors is reinforced by efforts to preserve the environment, human health, well-being, and sustainable construction that reduces CO2 emissions [3]. Considering the impact on the environment, the goal is to utilize raw wood materials more efficiently, and new wood-based materials are continuously developed and introduced to the market [4,5]. Attitudes about the influence of wood on the behavior and health of users are also being examined more intensively [6,7], as well as the possibilities of how wood in interiors can improve people’s well-being, comfort, and energy efficiency [8,9].

Wood is a biological material with inherent aesthetic properties that can give the final product a competitive advantage over other materials [10]. However, the main question that has been raised recently is whether the aesthetic appeal and positive emotional impact of wood can act as a holistic approach to health and well-being when staying indoors [11].

In the artistic sense, the feeling “It suits me, I like it” is related to the term “harmony” that is perceived by human senses (visual, tactile, auditory, olfactory). Namely, the aesthetic component of the product contains the basic principles of visual aesthetics (basic design), which in art is connected to the principles and elements of design [12,13,14]. Using design elements, aesthetic principles are realized that human beings recognize as “harmonious” or “incongruous”. This harmony is most often defined by an individual as “I like it” or “I do not like it” when making the first decision to buy a product.

Examining the visual aesthetic values of wood is not simple since wood is a natural material and has specific natural appearances (phenomena), so no wooden element (sample) is identical. The uniqueness of each wooden sample makes it difficult to accurately assess the user’s views on what they consider “harmonious”, since the color, shape, line, volume, or texture appear in different, and never the same, combinations [10].

In the past twenty years, the research on users’ attitudes about the perception of wood in interiors is increasingly widespread, and researchers use different methods in order to assess people’s preferences for a particular decor, wood appearance, color, texture, or pattern in a certain space [15,16,17,18,19,20,21,22,23,24,25].

The effects of visual exposure to wood on human affective states, physiological arousal, and cognitive performance [9], as well as the psychological benefit of using wood in interiors [26], were observed. People have an innate understanding that wood creates a healthy environment, and wooden rooms generally are positively perceived as “warm”, “comfortable”, “relaxing”, “natural”, and inviting/relaxing spaces [27,28]; the tactile, auditory, and visual perception of wood can be connected to emotions and certain attributes such as “expensiveness, solidity, rarity, interestingness, and sophistication” [29].

There is an increasing trend of biophilic design used in various places such as offices, restaurants, public spaces, schools, or universities [30,31]. Human inner feelings about nature and biophilia are connected with gestalt theory, visual perception, basic design (line, color, texture, structure, or shape) [12], stability of wood appearance, as well as the quality of individual wood sample (color, texture, knots or structure), which leads to a certain psychological feeling when the interior is filled with wood and wood products.

Understanding how the appearance of wood is processed in visual perception is crucial for the design of wood products and can help improve consumer satisfaction [32]. Today’s industrial mass production of wood strives to use the wood residue in the creation of new quality products on the market, with the aim of sustainability and nature protection. One such product is wooden wall coverings made from oak veneer residue [3]. For the wood industry in technological production, it is important to use those features of wood that have a great influence on customers’ choices of products. Customers expect quality from products, but questioning quality often leads to subjective criteria that are difficult to measure and are necessarily transformed through measurable methods [9,33].

When using wooden wall coverings to achieve harmony in the interior space, it is important to look at several features—how a person perceives and “feels” a certain decor and what psychological qualities he attributes to the decor that visually fills the wall surface in a functional interior.

This work raises the question of what if we want to be surrounded by a veneer that, according to its physical, technical, and technological properties, is considered waste in production but still, according to the principles of basic design, can be visually interesting and stimulate certain emotions in the potential user.

In the framework of the project “Research and development of innovative wooden wall coverings, partitions and load-bearing walls for sustainable construction in the company Spačva Ltd.”, which was carried out in the Spačva factory, Vinkovci, Croatia [34], one of the elements (activities) of the project dealt with the development of aesthetic designed interior wood paneling solutions using different natural-looking Pedunculate Slavonian oak veneer residues (Quercus robur L.) from the production process to increase the use of oak veneer residue. Characteristic appearances (wood phenomena) of oak veneer are singled out, which are defined in the factory as production–technological errors and often end up in the incinerator, but which, in a visual–aesthetic sense, create different visual appearances and could be acceptable for the design of harmonious decorative wall panels in interiors.

The research presented in this paper is a continuation of the research on the technological–aesthetic aspects of the veneer residue of oak veneers in Spačva Ltd., described in the previously published works of the authors [3,35,36].

2. The Aim of This Study

The aim of this research was to investigate the preferences of users for selected natural and unique appearances (phenomena) of oak veneer residue with the purpose of implementing wooden wall coverings in the interiors of public buildings.

Since this study is part of a project that investigates the possibilities of using veneer residue in a real factory, this research is of great importance for the specific case of using valuable Slavonian oak veneer that the factory throws away or burns and potential users could use newly designed products in interiors for specific purposes. Given that there was no previous information about which appearance potential customers prefer or do not accept, the survey questionnaire was intended to determine which decor the respondents prefer as visually more desirable and in which interior they would place it concerning activity, even though the presented appearances are a technological “error” and the residue.

The benefits and novelty of conducting this survey are the following: (1) Selecting specific phenomena that the factory treats as errors and researching user preferences for the four “rejected” phenomena—discoloration, wood rays, sapwood, and knots. It means not only any samples of phenomena and dimension of the decor but decors that were selected within the production process in the factory to reduce waste veneer, creating sustainable product and higher added value of the factory; (2) Obtaining answers about which veneer appearance is preferred by the respondents to show the factories the potential value of waste veneer and the direction of branding of their new products according to the target group of users; (3) Providing potential guidelines according to which appearance on wall panel should be implemented, depending on the phenomena, pattern, and dimension of the decor and the purpose of the interior; (4) Considering potential comments from respondents to improve the new procedure and research methods; (5) Obtaining guidelines and placing future higher quality research in real conditions; e.g., creating an interior with designed wall decorations in a functional interior of a specific purpose and enabling the implementation of a new survey.

3. Materials and Methods

The questionnaire was prepared in several stages. First of all, it was necessary to extract veneers with characteristic visual appearances at the factory, determine the dimensions of the decor, and cut, create, and surface process modules of defined dimensions. The decors were then photographed, and a 3D rendering of the interior was prepared, which would be used in the questionnaire. In addition, visual–tactile panels with test samples of decor were created and placed in two locations.

3.1. Samples of Wall Panels

3.1.1. Aesthetic Visual Appearances of Veneers

Various aesthetic–visual phenomena are singled out, which, in the technological sense, are considered errors, while in the aesthetic–visual sense, they open up possibilities for further research. The possibilities of utilization were considered according to the appearance (circle, line, texture, color) and annual amounts of waste in the factory that would give measurable results [3].

Based on the observed frequent errors of cut veneers from previous activities and confirmation of the same errors, the samples from the waste production process were separated and sorted into four visually different patterns (appearances) (I—knots; II—discoloration; III—wood rays; IV—sapwood) (Figure 1).

These four appearances were used as templates for four square-shaped decors in the survey questionnaire (

Table 1. Prepared decor templates with four appearances and surface treatments (© Mamić and Raguž Lučić, 2023).

Decor	Main Visual Appearance	Surface Treatments (Colors) of Decor Appearance
		(a) Natur Oil	(b) Snow White	(c) Walnut	(d) Black	(e) Light Grey
C1 discoloration
D1 wood rays
E1 sapwood-heartwood
F1 knots

).

3.1.2. Surface Treatment of Decor Appearances

To test the color preference in situ, samples with dimensions of 15 × 60 were made for four variants of finishing by oiling or painting in the following tones: (a) natural; (b) snow white; (c) walnut; (d) black; (e) light gray (Table 1) and placed on panels in both locations (polygons). In the questionnaire, the preferences for sample C1 in scaled dimensions 60 × 60 cm for all tones were examined.

3.1.3. Dimensions of Decor Modules

The initial dimension of the decor module concept of 60 × 60 cm was derived from the proportions of the most common height and width of walls in public spaces [35]. Considering the dimension of the identified production residue that will be used to make the module and technological feasibility [3], the width of the module should not exceed 35/40 cm, while a height of 60 cm is still adequate.

The next proposed concept was made of four decor modules with dimensions of 27.5 × 60 cm, 17 × 60 cm, 10 × 60 cm, and 6.5 × 60 cm. Proposals for dimensions and arrangement of modules are shown in Figure 2.

Due to greater modularity in the arrangement of decor modules in the vertical and horizontal direction, the dimensions of the modules and the number of decors, the dimensions of the modules were revised to the final dimensions of 60 × 60 cm, 30 × 60 cm, 15 × 60 cm, and 7.5 × 60 cm. According to these dimensions, samples were made for research purposes and placed in two locations (polygons).

3.2. Research Polygons

In addition to the online questionnaire, the survey was conducted using a QR code at two polygons:

(1)

Josip Juraj Strossmayer University in Osijek, Faculty of Civil Engineering and Architecture, Osijek, Croatia (Figure 3);

(2)

University of Zagreb, Faculty of Forestry and Wood Technology, Zagreb, Croatia (Figure 4).

A total of four panels with four different appearances (one panel—one appearance) were placed at the faculties in the cities of Osijek and Zagreb (C1-D1-E1-F1). Each panel is divided into four fields, so that at the top left, there was a decor in natural oil, with dimensions 60 × 60 cm; at the bottom left, there were samples in natural oil, with dimensions 30 × 60 cm, 15 × 60 cm and 7.5 × 60 cm; at the top right, there were the same dimensions of the decor (15 × 60 cm) in different surface treatments (tones), while the last part of the panel showed an image (3D render) of the space in which the observed appearance was arranged in a regular or irregular grid on the wall.

Panels with decor samples on which respondents could see and touch the decors were installed during May 2023, with the necessary corrections during June and July 2023 in both polygons.

3.3. Survey Questionnaire

The survey used a questionnaire created in the QuestionPro program. This questionnaire was divided into two main parts, (A) and (D), and contained a total of 43 questions.

To carry out the survey, samples (decors) of all four appearances (C1-D1-E1-F1) were photographed, and computer simulations were created for each appearance. Samples are prepared in Photoshop on a scale with dimensions of 60 × 60 cm and in other dimensions in two ways of stacking: regular raster for one dimension, 30 × 60; and irregular raster stacking by shearing the sample for modular dimensions of 7.5 × 60 cm, 15 × 60 cm, and 30 × 60 cm.

Some questions could be answered with more than one answer.

The questionnaire was distributed online and via QR code along with the displayed decors at polygons.

The introductory page of the survey questionnaire contained a short description of the project and the purpose of the questionnaire, as well as the question (confirmation) of whether the respondent would voluntarily participate in this research.

(A) group of questions (35 questions) was related to the presented appearances, where the respondents’ preferences for each appearance were examined by evaluating pairs of attributes, color evaluation, the way of arrangement in the interior, and connecting activities and functional rooms with the appearance.

(D) group of questions (8 questions) was related to general information about the respondents (age, gender, level of education, county of residence, size of place of residence).

For the A1 question, “How much do you like the particular displayed décor?”, a Lick-ert scale from −2 to +2 was used (I do not like it at all (−2); I do not like it (−1); I neither like it nor I dislike like it (0); I like it (+1); I really like it (+2)).

For all questions A2–A13 about the preference of decor in relation to the offered attribute and the way to arrange it on the wall (

Table 2. Decors and stacking arrangements for rating attributes.

Decor	Individual Decor/ Panel Dimension/ 60 × 60 cm	Regular Raster of the Decor on the Wall/ Same Dimensions of the Panels/ 30 × 60 cm	Irregular Raster of the Decor on the Wall/ Different Dimensions of the Panels/ 7.5 cm/15 cm/30 cm × 60 cm
C1 discoloration
D1 wood rays
E1 sapwood-heartwood
F1 knots

), a Lickert scale from −3 (negative attribute) to +3 (positive attribute) was used, where 0 indicated neither positive nor negative (e.g., extremely ugly (−3), very ugly (−2), ugly (−1); neither ugly nor beautiful (0), beautiful (+1), very beautiful (+2); extremely beautiful (+3)).

The attributes (pair of descriptions) that were evaluated were:

• ugly (−3)/beautiful (+3);
• boring (−3)/interesting (+3);
• artificial (−3)/natural (+3);
• cheap (−3)/expensive (+3);
• unpleasant (−3)/pleasant (+3);
• disturbing (−3)/calming (+3).

Each decor was evaluated in three ways using the above-mentioned attributes: as a single pattern, as a pattern arranged on the wall in a regular grid in panels with the same dimensions of 30 × 60 cm, and arranged on the wall as an irregular grid in panels of different dimensions 7.5 cm/15 cm/30 cm × 60 cm (Table 2).

In questions A14–A18, the preferences for decor E1 in finishing treatments by oiling or painting in the following tones: (a) nature; (b) snow white; (c) walnut; (d) black; (e) light-gray were examined. Attributes were rated from 1 to 5, where 1 corresponded to the least, and 5 corresponded to the most of the offered attribute. Attributes and decor with tones that were evaluated are shown in

Table 3. Decor E1 with tones and graded attributes.

Decor E1	Toned Samples	Attributes
(a) neutral		warm/cold natural/unnatural traditional/contemporary modern/old fashioned rustic/refined
(b) snow white
(c) walnut
(d) black
(e) light grey

.

In questions A19–A35, each basic decor (C1, D1, E1, F1) had to be connected with the activities and functional space offered. The activities and interiors offered to which each respondent could assign a single decor are listed in

Table 4. Decors C1, D1, E1, F1, related activities, and functional spaces (interiors).

Topic	Offered attributes and functional spaces in relation to the displayed decor
Decors
Activities	very quiet activity (sleeping, resting) quiet cognitive activity (work, study, reading, quiet conversation) medium-intensity activity (conversation, gathering, eating, walking, and moving) very intense activity (dancing, exercising, singing)
Functional spaces (interiors)	school classroom ambulance waiting room hotel reception hotel rooms sports hall restaurant	coffee shop religious building concert hall exhibition hall of the museum shopping mall hair salon library

.

3.4. Respondents

The survey was distributed online to members of professional associations (Society of Architects of the City of Osijek, Society of Civil Engineers of the City of Osijek, Croatian Design Society), employees and students of the Faculty of Civil Engineering and Architecture in Osijek, the Faculty of Forestry and Wood Technology in Zagreb, and other acquaintances of the partners.

3.5. Informative Content

Before starting to fill out the survey, respondents marked their informed consent with a tick in the introductory part of the survey questionnaire, thus confirming that their agreement and participation in this research were voluntary and anonymous and that they would not enter their identity information anywhere. Respondents could freely and without any consequences withdraw from further participation at any time without giving reasons. The entire procedure was anonymous. Additionally, approval and confirmation that this research was in accordance with the principles and rules of the Code of Ethics [37] were given by the University of Zagreb Ethics Committee and the Faculty of Forestry and Wood Technology.

4. Results and Discussion

The survey was conducted from July to December 2023.

The presented results refer to the mean values of the answers. In total, 82 respondents answered the questionnaire. The age and gender distribution, as well as the level of education and field of occupation or profession or study of the respondents, are shown in

Table 5. Total number of the respondents and distribution by age and gender, level of education, and field of occupation/profession/study.

	Age							Gender		Total
	<than 18	18–24	25–30	31–40	41–50	51–60	>than 60	M	F
N	0	20	10	21	15	11	5	35	47	82
Percentage	0%	24.39%	12.20%	25.61%	18.29%	13.41%	6.10%	42.68%	57.32%	100%
	Level of Education
	pupil	student	SSE	BSc	Mag.Ing./Art.		MSc	PhD	other	Total
N	0	23	0	2	28		9	18	2	82
Percentage	0%	28.05%	0%	2.44%	34.15%		10.98%	21.95%	2.44%	100%
	Field of Occupation/Profession/Study
	architecture	design	art	education	wood	forestry	economy	construction	law	other
N	13	14	1	4	27	2	4	14	1	2
Percentage	15.85%	17.07%	1.22%	4.88%	32.93%	2.44%	4.88%	17.07%	1.22%	2.44%

.

The largest number of respondents came from Osijek-Baranja County (42.68%), the City of Zagreb (21.95%), and Zagreb County (14.63%), which was to be expected since the sample panels were set up at the Faculty of Osijek (Osijek-Baranja county) and in Zagreb (City of Zagreb covers a lot of population from Zagreb County). Regardless of whether respondents saw live samples (43.21%), word of mouth and encouragement to complete the online survey were higher in these counties.

It should be noted that the averages shown in the results are not always for the same sample since some respondents started to fill out the survey but gave up in the meantime. For example, in some answers, the mean value for a certain attribute was calculated on a full sample of 82 people, but later, another mean value was calculated on a smaller sample of, for example, 75 respondents.

The presented results refer to the mean values of the answers.

Respondents’ preferences about “liking” samples showed that C1 and D1 decors led to desirability over other appearances (Figure 5). The least desirable decors are E1 and F1.

Preferences for the appearance of the decor in relation to the offered attributes: 1. ugly (−3)/beautiful (+3); 2. boring (−3)/interesting (+3); 3. artificial (−3)/natural (+3); 4. cheap (−3)/expensive (+3); 5. unpleasant (−3)/pleasant (+3); 6. disturbing (−3)/soothing (+3) are shown in Figure 6.

None of the decors were rated as boring, ugly, artificial, or cheap, but on the scale of “negative” attributes, decor E1 led the way as ugly, unpleasant, and disturbing, while decors C1 and D1 were rated as positive attributes (beautiful, soothing, pleasant). No decor has been rated with a maximum rating of +3 or under 0 or minus (−). The decor F1 looks the most natural.

A comparison of the results of individual decors C1, D1, E1, F1 (Figure 7, Figure 8, Figure 9 and Figure 10, blue columns), where the respondents observed each decor and then viewed it on 3D render when it was arranged in regular (Figure 7, Figure 8, Figure 9 and Figure 10, orange columns) or irregular rasters (Figure 7, Figure 8, Figure 9 and Figure 10, grey columns), indicates that matching of associations is not necessary. For example, the respondents evaluate decor C1 as more beautiful, natural, and pleasant (Figure 7, blue column), while when it is put together in a regular way of arrangement on the wall, it becomes uglier, cheaper, and more artificial and disturbing (Figure 7, orange columns), while with an irregular way of wall arrangement, the same decor is more beautiful, interesting, pleasant, and expensive (Figure 7, grey column).

Similar responses in different preferences can be observed on other decors (Figure 8, Figure 9 and Figure 10). The biggest difference in decor preference is for decor E1, which received the most negative attributes (unpleasant, disturbing, even ugly) in both regular and irregular wall arrangements (Figure 9, orange and grey columns), although it was rated more positively when viewed as an individual sample (Figure 9, blue columns).

The results confirmed that of the offered decors, the respondents considered the appearance of C1 and D1 to be the most visually harmonious (“prettiest”) (Figure 6), and they confirmed the same preferences for these decors in the interior displays (Figure 7 and Figure 8), where both have more positive attributes in the regular and irregular arrangements of panels on the wall.

The least desirable decor is the combination of sapwood–heartwood appearance (E1), and on the scale of the desirability of stacking on the walls in the regular stacking mode, it is rated as extremely ugly, unpleasant, and disturbing (Figure 6 and Figure 9) while it is more desirable in the irregular stacking mode on the wall (Figure 10). Decor F1 is considered the most natural, interesting, and beautiful (Figure 10, blue columns) but is preferable in an irregular arrangement on the wall than a regular one (Figure 10, grey columns).

The connections between the decor and the offered activity and functional space (interior) are listed in

Table 6. The connection between the decor and the offered activity and functional space (interior).

	Decor	C1		D1		E1		F1
	Sex	M	F	M	F	M	F	M	F
activity	A19—very quiet activity	14.71%	27.66%	73.53%	65.96%	5.88%	0.00%	5.88%	6.38%
	A20—quiet cognitive activity	57.14%	34.04%	20.00%	48.94%	2.86%	0.00%	20.00%	17.02%
	A21—medium-intensity activity	17.14%	46.81%	14.29%	4.26%	37.14%	17.02%	31.43%	31.91%
	A22—very intense activity	8.57%	25.53%	8.57%	4.26%	48.57%	40.43%	34.29%	29.79%
Functional space (interior)	A23—school classroom	34.29%	38.30%	51.43%	46.81%	2.86%	2.13%	11.43%	12.77%
	A24—ambulance waiting room	20.00%	27.66%	57.14%	59.57%	8.57%	6.38%	14.29%	6.38%
	A25—hotel reception	22.86%	25.53%	25.71%	21.28%	22.86%	21.28%	28.57%	31.91%
	A26—hotel rooms	35.48%	37.78%	32.26%	44.44%	16.13%	4.44%	16.13%	13.33%
	A27—sports hall	28.57%	29.79%	34.29%	34.04%	25.71%	21.28%	11.43%	14.89%
	A28—restaurant	28.57%	40.43%	14.29%	17.02%	11.43%	8.51%	45.71%	34.04%
	A29—coffee shop	28.13%	25.00%	9.38%	9.09%	46.88%	29.55%	15.63%	36.36%
	A30—religious building	22.86%	14.89%	48.57%	51.06%	5.71%	10.64%	22.86%	23.40%
	A31—concert hall	22.86%	26.09%	31.43%	41.30%	20.00%	10.87%	25.71%	21.74%
	A32—exhibition hall of the museum	20.00%	25.53%	54.29%	48.94%	14.29%	10.64%	11.43%	14.89%
	A33—shopping mall	14.29%	20.45%	25.71%	27.27%	25.71%	34.09%	34.29%	18.18%
	A34—hair salon	30.30%	41.30%	27.27%	13.04%	18.18%	21.74%	24.24%	23.91%
	A35—library	40.00%	41.30%	42.86%	41.30%	5.71%	2.17%	11.43%	15.22%

Marked results as bold orange, bold green, and bold gray are respondents’ highest preferences: bold orange = highest preference; bold green = higher preference; and bold gray = high preference within selected responses.

, where the percentage of the respondent’s greatest preference for a particular decor is marked as bold and with a different color. Since this set of questions could be answered with more than one answer, all three bold-marked results were considered the highest preference (bold orange indicates the respondent’s highest preference; bold green indicates a somewhat lower preference, and bold grey even a lower preference). It is interesting to observe how, in the preferences for certain decors and activities, as well as the connection of attributes with the purpose of the space, there are identical attitudes of respondents with regard to gender, while for some decors, the answers differ according to gender.

Thus, respondents for decor C1 prefer quiet cognitive activity (M = 57.14%) and medium-intensive activity (F = 46%) for spaces where reading and learning were expected in silence, such as libraries (M = 40.00%; F = 41.30%) or school classrooms (34.29%, 38.30%). Men associate F1 decor with extremely intense activities (M = 34.29%), like in dynamic spaces such as restaurants (M = 45.71%) or hotel receptions (M = 28.57%), while women would mostly choose F1 for medium-intensity activities (F = 31.91%) like in coffee shops (F = 36.36%) or hotel receptions (F = 31.91%). Both genders associate the same activities with decor D1 and E1. D1 is seen as desirable for very quiet activity (M = 73.53%; F = 65.96%), where silence and a peaceful, quiet atmosphere are expected, such as in ambulance waiting rooms (M = 57.14%; F = 59.57%), religious buildings (M = 48.57%; F = 51.06%), or museums (M = 54.29%; F = 48.94%). Decor E1 would place both genders with extremely intense activity (M = 48.57%; F = 40.43%), such as music, talks, walking, or noise in coffee shops (M = 46.88%; F = 29.55%) and shopping malls (M = 25.71%; F = 34.09%). At the end of the questionnaire, respondents were able to write comments or suggestions for improving the survey. One respondent particularly emphasized the opinion that “The cleaner the element (without additional stripes, dots, or color changes) and the cooler the color (lighter, not darker), the better it gives a calming effect”. Another respondent emphasized, “I don’t find it visually beautiful, maybe even boring, to place or line up veneers on monolithic walls like ceramic tiles of exactly the same texture with the same repeating wood errors. This is especially true of “rustic” veneers with the same knots or sapwood or some other flaw in the order as they are cut and arranged into packages or artificial surface decorations. I would like it better if these errors were different (they can be the same) and the veneers were composed without any regular sequence and from different modules. I assume that, in reality, the veneers, albeit with typical errors, would be mixed up a bit from different packages before stacking. In the case of veneers with a uniform texture, this is less pronounced or important, but in the case of the appearances shown here (especially the sapwood or the knots), it significantly affects the visual harmony or restlessness”.

The results confirmed that despite the trends of biophilic, natural, and unique visually decorative surfaces, the surveyed group of potential users mostly singled out discoloration and wood rays as the most harmonious (“most beautiful”) decors, even though these decors looked the least unique—they were visually similar; wood irregularities were least noticeable, and such “mistakes” could be seen in most classes of healthy veneers and were even technologically acceptable.

Furthermore, phenomena containing a combination of sapwood and heartwood, which can largely depend on the proportion of sapwood and heartwood in the decor, were rated as the least desirable. If the heartwood (the darker part of the wood) was completely removed or its share in the decor was reduced, the sapwood would look like a healthy wood with a straight section, and probably, the respondents’ preference for such a decor would give different results, especially if they did not know the technological disadvantages of sapwood.

Although there are a lot of works that have recently dealt with researching the impact of wood on the feelings and well-being of respondents [6,7,8,9,10,11,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32], there are not many works that investigate whether waste veneer from the factory is desirable for further use and design of wall coverings that customers will evaluate as visually desirable for certain activities or functional interiors.

This research is of great importance for the specific case of using the valuable Slavonian oak veneer (Quercus robur L.) that the factory throws away or burns, and they could potentially achieve a higher added value of a sustainable product and the ecological sensibility of customers with a good design. Considering that there was no previous information about which veneer appearance potential customers prefer or do not accept, the results of the survey questionnaire determined which particular decor the respondents preferred as visually more desirable and in which interior they would place it, considering the activity. This research gives the company design guidelines for the development of sustainable products and can significantly help designers and architects when designing interiors for a specific purpose and function where a certain way of behavior and psychological stimulation is desirable. A summary of the proposed design guidelines according to the obtained results can be found in

Table 7. Proposed design guidelines according to the obtained respondent’s preferences.

Decor	Display	Design Guidelines/Attributes, Activities, and Functional Interiors
C1 discoloration		- potential users like the discoloration and find it very beautiful, interesting, natural, expensive, very pleasant, and very calming; - recommended for spaces where quiet cognitive or medium-intensity activities are performed, such as quiet work, reading, studying, quiet conversation or gathering, eating, passing, and moving; - suggested for equipping interiors such as school classrooms, hotel rooms, libraries, or even restaurants where an intimate atmosphere is desirable; - irregular arrangement of decor on the wall is preferred as it is considered very beautiful, very interesting, natural, very expensive, very pleasant, and very calming. Note: - the company should pay more attention to the production of waste veneers with discoloration; - the design of new combinations of decors on the wall is desirable; - new research in real-world settings is needed.
D1 wood rays		- potential users like it and find it very beautiful, interesting, very natural, expensive, very pleasant, very calming; - recommended for spaces where very quiet physical or cognitive activities are performed, such as sleeping, resting or quiet work, reading, studying. Additionally, it is recommended for spaces with medium-intensity activity such as conversation, gathering, consumption of food, passing, and movement; - suggested for equipping interiors such as school classrooms, ambulance waiting rooms, hotel rooms, or religious buildings; - irregular arrangement of decor on the wall is preferred as it is considered very beautiful, very interesting, natural, very expensive, very pleasant, and very calming. Note: - the company should pay more attention to the production of vaste veneers with wood rays; - the design of new combinations of decors on the wall is desirable; - new research in real-world settings is needed.
E1 sapwood-heartwood		- potential users do not like it but find it interesting and natural; - recommended for areas with very intense activity such as dancing, exercising, singing; - suggests furnishing interiors such as sports halls, coffee shops, shopping malls, or hair salons; - both regular and irregular arrangements of decor on the wall are ugly, unpleasant, disturbing, but interesting. Note: - further research into the sapwood–heartwood relationship in decor is necessary; - it is suggested to increase the proportion of sapwood in the décor; - new research in real-world settings is needed.
F1 knots		- potential users like it and find it beautiful, interesting, natural, expensive, and pleasant; - recommended for spaces with very or medium intense activity such as dancing, exercising, singing, conversation, gathering, consumption of food, passing, and movement; - suggested equipping interiors such as hotel receptions, restaurants, or coffee shops; - both regular and irregular arrangements of decor on the wall are preferred and considered beautiful, very interesting, natural, expensive, pleasant, and calming. Note: - the company should pay more attention to the production of vaste veneers with knots; - new research in real-world settings is needed; - the design of new combinations of decors on the wall is desirable.

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Although this research gives significant results on the preferences of potential users and provides instructions for the design of wooden wall coverings, it simultaneously points to limitations that lie in the inability to present and unify all appearances, the application of different dimensions of panels in different directions, and countless surface treatments of decor from the remains of oak veneer. Limitations in the display of decor in only one combination of placement on the wall or one used in the interior reduced the value of individual decor. The finish is also limited to a few colors. This research used oils and varnishes that the manufacturer uses in parquet processing, but the suggested color shades do not necessarily have to be identical to the surface colors of the parquet. Moreover, in order to remove the monotony from the space, it is suggested to use other, perhaps even contrasting, tones on the walls compared to the colors of the floor coverings.

Additionally, the survey questionnaire used 3D renderings of a photo of a pattern of appearance that was multiplied on the wall surface like ceramic tiles. This visual reproducibility and “sameness” were noticed by the respondents, who left their comments and pointed out possible improvements in future survey questionnaires.

A potential example for further research would be a different proportion ratio of sapwood and heartwood, which reduces the great contrast emphasized here (most noticeable in the regularly placed decor on the wall). By bleaching veneers with this appearance, a more visually balanced decor would be achieved while retaining the character of this appearance as well. Following this, further research should include more visual design and technological intervention in the preparation of veneers and combinations of surface treatment and, thus, intervene in the visual appearance of the relationship between sapwood and heartwood. Another example is wooden rays that do not have absorbent properties like sapwood or the rest of the wood, and it is possible to obtain visual dynamics of the decor by applying elements and principles of basic design (rhythm, harmony, contrast, emphasis).

5. Conclusions

The results of this research showed the preferences of the users according to the offered appearances of Pedunculate Slavonian Oak (Quercus robur L.), which in the production technology is considered a residue but potentially has positive visual aesthetic properties. Four visual appearances of discoloration, wood rays, a combination of sapwood–heartwood, and knots were investigated on decors of different dimensions, for which it was necessary to determine the user’s preference on the visual desirability of the veneer in order for the company to decide which appearance could potentially be commercially more profitable for the design of sustainable decorative wall covering from the rest of the oak veneer.

The topics of this research offer countless design and architectural possibilities but provide certain guidelines as future recommendations for the company or architects and designers. Potential users do not see appearances as waste veneers but perceive the displayed decor as a more or less harmonious visual aesthetic, which the company should keep in mind when using its expensive raw materials and designing new sustainable ecological products.

For further product design, it is suggested to make the most of veneers that contain discoloration or wood rays and arrange them in regular grids on the wall in interiors that need quieter activities, such as libraries, school classrooms, ambulance waiting rooms, or religious buildings. Decors that contain knots are considered the most natural visual appearances and are suggested to be used in areas with very or medium intense activity, such as restaurants, coffee shops, or hotel receptions, but attention must be paid to the way wall decors are arranged in the space so that they do not become ugly and disturbing. Decors that contain combinations of hardwood and sapwood are subject to further research and improvement since they are not evaluated as desirable or beautiful, and in the combination of stacking on the wall, they are even declared disturbing and unpleasant. In the future design of these decors, their ratio should be considered, whereby the part of the veneer containing sapwood must be increased in order to stand out and be visually desirable.

In relation to surface treatments and colors, if warmth, naturalness, traditional, and rustic expression are desired from the interior, it is recommended to use tones such as black or snow white. The walnut tone is recommended for modern, non-traditional, contemporary, and not very natural interiors. For further research, it is recommended to apply design and visual design methods as a basis for technological preparation and potentially develop the appearance into a defined decor with predetermined tones that are most suitable for that appearance.

It should be focused on research in real-world conditions and confirmation of the positive impact of wooden wall coverings made of expensive oak residue on the natural environment, the symbiosis with natural, biophilic design, the impact on the well-being and health of users in the interiors of residential and public buildings, as well as on the branding of a new environmentally friendly product made from of wood residues in the company Spačva Ltd. Vinkovci, Croatia [34] It will be of great value to obtain objective data on consumer preferences for wooden wall coverings from the rest of the veneer in real interiors and to analyze data on the purchase of this group of products on the market.

6. Patents

The project “Research and development of innovative wooden wall coverings, partitions and load-bearing walls for sustainable construction in the company Spačva Ltd.” as part of project activity 5 “Development of aesthetic and design solutions of the interior using veneer wall coverings with different natural phenomena with the aim of increasing the use of veneer logs” resulted in the application of a patent/industrial design for the design of wooden wall coverings, number 25-01, ID No. EFHR20230000000568. The authors of this work are the designers of the applied industrial design.