Steaming Walnut for Color

The objective of this study was to determine the relationships between rates and degrees of color change in walnut exposed to steam temperatures of 212? F. and above. Most of the experimental work was conducted in a small retort capable of holding 60 board feet of lumber. Mixed sapwood and heartwood samples of walnut were subjected to various temperatures of live steam for given time intervals. For every test sample, an end-matched control sample was taken so that the original color and final color could be directly observed. The degree and rate of change in color was found to be dependent upon temperature, moisture in the stock, and time of exposure. Darkening of sapwood takes place uniformly through the width and depth of the sapwood. The rate or speed of color change in sapwood increases as the temperature of the stock is increased. With steam exposure the amount of color change increases rapidly in the first 4 to 6 hours. The heartwood changes in color slightly and slowly at 212? F. Moisture in the wood plays an important role in the color changing process. Green stock darkens sooner than air-dried stock. Green lumber steamed at 230? F. will tend to dry rapidly if it is allowed to come in contact with cool air immediately after steaming, thus an overnight cooling in the retort should be allowed.

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