Although distinction between heartwood and sapwood is important to inspect penetration of preservative chemicals, the decrease of color differences between heartwood and sapwood due to high-temperature drying of Sugi (Cryptomeria japonica D. Don) timber results in difficulty to distinguish each other. Therefore, coloration of high-temperature dried Sugi timber was examined by eighteen chemical reagents. The changes in color were evaluated by color differences (ΔE*).
The treatment by NaOH or KOH solution stained the heartwood in blue-black and gave ΔE* sufficent to distinguish the heartwood from the sapwood. These chemicals were also effective to stain the heartwood of high-temperature dried Sugi timber after treatment with several preservatives. Thus, this technique can be used as a coloring indicators of high-temperature dried Sugi heartwood.

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