Surface colour change in wood during drying above and below fibre saturation point
A technique has been developed to measure the surface colour change in a single wood sample during drying. This method is useful for studying the development of kiln brown stain. The wood sample is planed carefully in the green state to remove any surface wood that was damaged during cutting. This exposes intact tracheids at the surface rather than the damaged tracheids normally found at the surface of rough-sawn timber. The intact tracheids cause the evaporative front to remain at the surface during drying and therefore colour formation also occurs right at the surface. This means that the colour can be measured using a spectrophotometer at various stages during drying without having to slice the sample. This reduces errors associated comparing matched or unmatched samples. Experiments were carried out to measure the change in colour of wood from green to EMC at different schedules. At the end of each schedule the boards were held at the EMC to determine how the colour changed below fibre saturation point. The results show that the colour of the wood continues to change below fibre saturation point and the nature of the colour change indicates an increase in the complexity of the coloured compounds present.