Means to measure the aesthetic properties of wood

Abstract: Wood is a biological material with inherent aesthetic properties which can give the final product a competitive advantage over other materials. In this thesis, people’s feelings and preferences for Scots pine (Pinus sylvestris) wood surfaces have been examined. The main objectives of this thesis are to develop methods for measuring people’s preferences toward different looks of wood and to connect the subjective preference data with objective measurements of wood features. It comprises both qualitative and quantitative methods for collecting preference data. Two projection methods, PCA and PLS, were used to analyze the quantitative studies. Interviews made clear that people prefer different blends of wood features. There are two qualitative differences that are of importance for people's impressions and valuations of wood: The overall blend of wood features and divergent features that mismatch in a surface. It was found that divergent features are more important than the overall mixture of features. But if there are no defects that mismatch, the overall mixture will then be the key to a person's appreciation of a wood surface. Wood surfaces should stimulate people's interest and be fresh looking. A clear surface is naturally rather harmonious, elegant and easy to look at. On the other hand, a clear surface should be stimulating to look at, should be exciting and it should not look like an imitation. Knotty surfaces usually are less harmonious. Therefore, questions about harmony, easiness to look at and balance are of importance. Just as for clear surfaces, a knotty surface should also stimulate people's interest, have a fresh look, be exciting and stimulating to look at. The quantitative studies show that it is possible to measure people’s preferences toward wood by a questionnaire technique. The results also show that there are differences in people’s judgments for surfaces with knots and for those without knots. There are stronger connections between questions regarding the overall impression and the final assessment than there are for detailed questions regarding certain wood features. Thirteen questions were pointed out as relevant to use with interviews. Two interview methods were compared. The first method used wood surfaces and the second used computer images with the same wood surfaces applied to an example product, a kitchen cabinet. The results show that the two methods are comparable and useful. It was shown that it is possible to some extent to connect subjective preference data with objective wood feature measurements. Results show that a lot of wood feature measurements are needed and that it is a multivariate problem. Concerning the measurements, it seems easier to find features that negatively affect people’s liking than to find the opposite. Among the most important variables were those that detect different kinds of feature distribution over a wood surface, and especially those variables that detect a deviation in center of gravity. Increased knowledge about people’s preferences for the aesthetic properties of wood will lead to a better understanding of which wood features should be measured and controlled in the future.