Walnut has a lot of sapwood. I have heard that it can be steamed (or something) during the kiln drying process to “activate” the colors that are in the sapwood, making the sapwood much darker – much closer to the color of the heartwood.
Lately much of the walnut I have been able to find locally has a high percentage of sapwood. Either they aren’t bothering with the “steaming” or that is really an old wives tale. Is it possible to do something to walnut that has already been dried, to activate the latent color of the sapwood? Casually steaming it with a steam iron doesn’t work (I didn’t expect it would, but I tried).
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Charlie Plesums Austin, Texas
www.plesums.com/wood
Replies
Charlie, It has been my experience that steamed walnut is somewhat dull and unsatisfying. I have never heard of the sap wood having latent pigment. I used to try to cut the sap wood out, now I make use of the contrast which I think is nice, especially if the wood is not steamed and the sap wood is white. If I don't want any sap I order 10" and wider walnut which is about 1$ more per bd ft. It still has some sap but when I'm finished trimming I'm left with a decent width.
Bill Lindau
Virtually all commercial walnut that I've found is steamed. Unsteamed has purple highlights when fresh rather than brown and a lot more variation in color. The purple eventually gets brown with time. The sapwood stays white regardless.
Charlie, the mills steam walnut while the lumber is "green"...meaning as soon as it has been cut from the log and still has a high moisture content. Once steamed, it is then kiln dried.
The heat the wood is exposed to when steamed causes the extractives in the sapwood to darken (as opposed to causing them to migrate from the heartwood into the sapwood), but the process doesn't work as well if the wood has been allowed to air dry prior to steaming.
I prefer working with air dried walnut even though it means trimming off the sapwood, but I usually find a use for the trimmings in other projects. In situations where I have to touch up the sapwood edge of a board that I can't trim off completely, I like to use a home brewed walnut husk stain. It's made by simply soaking walnut husks in a jar of non sudsing ammonia until the liquid turns dark. This stain can then be diluted with water and applied in successive coats to build up just the right amount of genuine walnut pigment in the sapwood edge.
Jon -
I thought steam was injected into the kiln at intervals during the entire drying process to prevent case hardening and checking. Is that not true? I.E. - trying to get the wood at the surface to dry at the same rate as the interior wood. Since most shrinkage generally occurres in the 10 - 20% EMC range, that would be the time I would think steam would be injected.
PlaneWood by Mike_in_Katy (maker of fine sawdust!)PlaneWood
Mike, steam is used in the kiln drying process to minimize stress, as you've described...but steaming for color is normally done prior to kiln drying. There are various levels of sophistication as to how to go about it. All that is really needed is a chamber that can be injected with steam. However, the speed with which the pigments are formed is a function of the temperature and the process can be accelerated if the temperature is taken above the boiling point of water to somewhere around 230 degrees F...But you can't do this unless the chamber can be pressurized...So, depending upon how well the process is controlled, it can take anywhere from a couple of days to as much as a week to coax the extractives in the sapwood to polymerize into pigments.
Once the desired color is achieved, the wood (which is still thoroughly saturated) is dried in the conventional way in kiln...and in accordance with the schedule for the species. Some woods that tend to be difficult to dry are pre steamed...not for color, but because steaming the wood shortens the kiln drying schedule and also helps to prevent degrade. Operating a kiln correctly requires some smarts and a good kiln operator is a very valuable specialist in the lumber industry.
Thanks Jon. I never knew they injected steam solely for color. I thought that was just a by-product.
PlaneWood by Mike_in_Katy (maker of fine sawdust!)PlaneWood
Jon, thanks for your clear and expert answer... as always.
Lately it seems that practically every walnut board purchased in Texas has one surface largely sapwood, which makes doors and boxes hard. I have been using the pieces that are mostly sapwood for drawer sides and other "secondary" uses, and have been playing with various dyes (often applied with a Q-tip) to hide isolated spots. I was hoping for a miracle - it would have been nice <grin>. ________________________Charlie Plesums Austin, Texashttp://www.plesums.com/wood
Charles -
How much walnut do you buy? I got about 12,000 bf standing up in the Ozarks of OK. Trees are 2' or greater diameter. Was going to log them out last winter but spent all my money on something else (typical occurrence).
PlaneWood by Mike_in_Katy (maker of fine sawdust!)PlaneWood
I am still a part-time woodworker, negotiating with my wife/accountant about taking early retirement. Thus my woodworking varies tremendously (for now), depending on what is happening at work and thus how much time I have available in the workshop. I have bought over 100 boardfeet at a time for projects, and would use a higher percentage of solid rather than plywood if good stuff was available, but currently I am on the road for my day job so the woodshop "isn't" getting as dusty as I would like.
My real problem is storage - I have to buy on a project-by-project basis, and cannot dry my own lumber (I live in the city, with no room for outbuildings). I have been able to track down good wood, but in far-away places (like Iowa) where the cost of shipping smaller quantities is a killer.
I didn't figure there was a magic wand, but I also figured Jon Arno and the others on this forum would know if there was. ________________________Charlie Plesums Austin, Texashttp://www.plesums.com/wood
I took a class a decade or two ago and was told/shown " ??something permanganate". Probably spelled wrong, but maybe someone here can clarify.
Steamed is definitely dull looking.
Chief
Potassium permanganate is a strong oxidizer. Purple color in solution, but turns wood brown and darker. You can buy it in the plumbing department since its used to recharge certain types of water treatment units. Reasonably poisonous. Potassium dichromate gives a yellow color that ages to brown. Highly toxic and carcinogenic. Lots more chemical wood treatments. Natural walnut stain from husks works fine and is fairly safe.
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