Steaming Walnut

      If you do it properly, steaming walnut brings color to the sapwood without destroying the figure in the heartwood. May 11, 2005

Question
Is there any detailed literature on steaming walnut, including chamber construction, boiler sizes or perhaps another way of generating steam, and step by step instructions? I'm looking to steam 2000 to 3000 bf of 4/4 at a time.

Forum Responses
(Sawing and Drying Forum)
From contributor K:
Why would you want to ruin wood like that? The steamed walnut that I see in some of the large commercial kiln outfits around here looks like garbage. A milk chocolate brown that has no discernable character. Most of my customers, including some high end manufacturers of specialty products, specifically request me not to steam my walnut.



From the original questioner:
I agree with you, but this is for one of my biggest customers, who uses it for low end high production promotional pieces where quality takes a back seat to quantity. He in fact is requesting I look into it to boost his production and minimize his losses in sapwood.


From Gene Wengert, forum technical advisor:
If properly steamed, walnut will have beautiful color. The problem is that some people do not steam properly and get the wood too hot or too cold. There are many steamers that do a beautiful job. For more details, see US Dept of Agric Handbook No. 528, "Drying Eastern Hardwood Lumber." It was published in 1976 and is now out of print. This should be available through all libraries - interlibrary loan if they do not have it themselves. If you are a member of the NHLA, contact Dusty Moller there and he can probably make a copy of the steamer pages or may even have some extra copies.


From contributor D:
When you do steam, I suggest that you put an RTD or two in the wood and then heat only as hot and as long as needed to change the color of the sapwood. I think you'll find that you do not need to get the wood as hot as many people believe and the color of the heart wood won't be changed.


From the original questioner:
Please forgive my ignorance. What is a RTD?


From contributor D:
They are solid state devices (resistance) for remote temperature sensing. They are accurate, rugged, fairly cheap (about $60) and can be read by a variety of instruments.Also, they need no special wire for extensions and can be extended 1000's of feet and still give an accurate measurement (if they are 3-wire).


From Gene Wengert, forum technical advisor:
RTD = resistance temperature device. Often the device is in the shape of a round wooden pencil with a small piece of platinum wire at the tip (but inside so you cannot see it or damage it easily). The resistance of the platinum wire changes with temperature in a predictable manner, so if you know the resistance, you know the temperature. We use three wires, so that the resistance change in the wires (for whatever reason) can be accounted for and not incorrectly influence the reading of the platinum wire resistance.

Incidentally, the steaming chamber must be at 100% RH. The wood must get to about 180 F for best color development and this means that the temperature in the steamer must be around 210 F. Cooler temperatures work, but they take longer and do not get as good color (although even 180 is pretty good with a wood temperature of 160 or so).

Note that you may have run-off from the steamer and this run-off is a pollutant in every state, by federal law. The fact that some states do not enforce the law still does not make polluting with the run-off okay. The run-off is an herbicide.



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