Bleached-out streaks in air-dryed walnut?

[Jamie Buxton]

I have a friend who's been harvesting and air-drying Claro walnut. The dry slabs look okay, but when I cut into them, there are light-colored streaks inside. The bleached-out areas are not visible on the surface of the slab. They become evident only when some of the surface is removed. In the first photo, you can see an area where I've planed off just a smidge, and the walnut is normal color. Lower in the photo, you can see where I've planed off a deeper cut, and the bleached areas appear. The bleached areas are not sap wood. In the second photo, you can see sap wood near to the bark. It is a different color and grain texture from the bleached areas.

If it makes any difference, the slabs are 2 1/2" thick, and have air-dryed in California's Central Valley for three years. In the summer, they regularly see daytime highs of a hundred degrees, and relative humidity below 20 percent.

Does anybody know what's going on here?
And does anybody know what to do to not have it happen in the future?

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[Lars Larson]

I believe that kiln drying evens out the coloring between the sap and heart wood because of the way that the water is drawn out. Due to the fact that your lumber is air dried you actually get the natural amount of contrast between the different layers.

From what I understand the dark part of the wood will be a bit darker than with kiln dried and the sapwood will really stand out.

Lars

[Tom Fischer]

Yes, not a fan of kiln drying, but some steaming would have evened out the colors.
Also, I once met a bowl turner guy. He said he usually left walnut blanks out in the rain for a few months before air drying them. Apparently, that will help to even out the natural dyes.
Years ago, I wanted to steam bend some walnut. So, being not too smart, I put it in the Dear Wife's dishwasher, on steam cycle. Nearly turned the inside of the diswasher black. Thought I was a dead man walking. :D But the walnut dye didn't stick permanently to the inside of the dishwasher, factory enamel paint and such. I lived to see another day.
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I think you are seeing a mixture of sapwood and heartwood. The tree just does what it wants.
My suspicion is that walnuts get their color from stuff in the ground.
My neighbor gave me a couple of black walnut trees a few years ago. One was growing in black mud. Some of the lumber looks like that.

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Tomorrow I will look at that black walnut stack again. Probably some boards in there like you have as well.

[Conrad Fiore]

Jamie,
Just for kicks, plane a good section smooth and wipe it down with some mineral spirits. You might have an interesting figure going there.

[phil harold]

normal walnut
steaming walnut will minimize color contrast
sun will bleach it all to the lighter color
best bet is to stain or dye for lasting effect

[Scott T Smith]

Jamie, I have seen similar streaks in claro walnut that was not fully dry. The ones that I have seen have a slight green tinge to them.

My experience is that it takes two to three times longer to air dry claro as opposed to black walnut, that you have to be very carful not to dry it too quickly, and that it is not a good candidate for kiln drying. Once dry, the colors can be absolutely spectacular, but you have to be patient.

I would give your slabs about another three years of air drying.

[Sean Hughto]

Looks normal to me. Here's a walnut bowl, I recently finish turned - you can see similar coloring. I personally prefer this to the steamed look.

http://farm7.staticflickr.com/6114/6316460723_d2e4d5ac97_b.jpg

[Phil Thien]

I'm afraid that wood is completely contaminated. Better just send it to me.

[Jamie Buxton]

I've talked to the guy who milled the slabs. He says those streaks weren't there when he cut the wood. That is, they happened during the drying process. My guess, based on little actual knowledge, is that the streaks are caused by some microrganism that's attacking the walnut. The immediate surface of the slab gets fairly dry fairly quickly, so the microrganism can't thrive there. That's why the streaks are not on the surface. However, during the 3 years the walnut has been airdrying, the interior of the slab has been wet enough for the microrganism to do well.

BTW, after three years of drying, this slab is 12% humidity.