Wood color control during kiln-drying

The coloration of wood during drying in a laboratory kiln was investigated and modelled using multivariate techniques: principal component analysis and partial least squares (PLS). The wood species included were Scots pine (Pinus sylvestris L.), Norway spruce (Picea abies [L.] H. Karst), and birch (Betula pubescens Ehrh.). Color changes were determined at the unplaned surface and after planing off 1 and 3 mm from the surface using a photoelectric colorimeter. Color parameters presented were lightness, chroma, and hue. PLS models for the color for each species was a useful method and the results indicated possibilities for future batch-color control of kiln-drying. The coloration of the wood was equally intense during the kiln-drying when free water was present (early part) compared to when no free water was present in the wood (late part). The coloration was most intense at the wood surface, however, planing removes the major coloration induced by drying. Color homogeneity was not found to be affected by raised temperatures during drying.