Q. We buy steamed walnut. Sometimes we love the results. Other times, the color is not very uniform. What should we use to judge the customer's steaming process?
A. When steaming walnut, we are trying to color the white sapwood so it looks quite dark. We are also trying to color the heartwood so it is chocolate brown throughout the lumber. We accomplish our goals with heat at around 200F. However, we also need to use 100 percent RH. This high humidity prevents the lumber from drying during steaming. If the humidity is under 100 percent, then end checks and even some internal checks are likely, especially around knots; plus the color will not be as good.
So, the people steaming your lumber should inject steam into the chamber with the steam pipe being submerged in a trough of water to assure 100 percent RH. They should be running the steamer's environment at 195 to 210 F. Steaming time should be around three days. We get the best results when the incoming lumber is freshly sawn; partly dried lumber should not be steamed.
If you want specific details, see pages 61+ in Drying Eastern Hardwood Lumber, which you find on the Internet.
Gene Wengert, “The Wood Doctor” has been training people in efficient use of wood for 35 years. He is extension specialist emeritus at the University of Wisconsin-Madison.
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