Green Color of Freshly Sawn Walnut

      Freshly cut Walnut's green tinge disappears with time and exposure to air. February 17, 2014

Question (WOODWEB Member) :
We're a small hardwood flooring MFG and are tasked with making a small walnut end grain floor. In the past we've made these from walnut beams (5"x5") that we cut from logs. This time we had to get some logs. Once we started cutting we noticed that the pieces are very green in appearance. This looks like none of the KD walnut we usually deal with. I know walnut gets steamed to even out the sap, but I don't think I'm looking at sap (none of this has been steamed).

The brown block on the left has been around here for years, the other three were fresh cut from logs. The next picture is the outside of a couple beams (old vs. new). The last pic is a board cut from the fresh stuff. The brown stuff has been cut probably three-four years ago and air drying since. I need the brown color. What is the green colored stuff I have?

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Forum Responses
(Sawing and Drying Forum)
From Gene Wengert, forum technical advisor:
Some walnut is green but will darken with drying and exposure to light. Heat helps darken, so run the kiln at 160 F during part of the schedule.

From the original questioner:
We're going to be putting them in the kiln next week, but in the meantime I'm experimenting with a microwave. I've got a few blocks down to 6% and they’re still green. Does the color have anything to do with region, or age of tree?

From Gene Wengert, forum technical advisor:
It takes time for the color reaction to happen, so fast drying in a microwave will not work.

From the original questioner:
What sort of time frame would it take? I know there a ton of variables. Should I see change in a few weeks or months?

From contributor M:
All of the black walnut here in Oregon has a green tint to it when freshly sawn from the log. Do not be worried about this, it is normal. As the wood dries it will turn the usual walnut tones of brown and will lose the green color, just like the beams you have worked with in the past.

Once the wood has gone through normal kiln drying cycle, (or if it is air-dried first, then to the kiln) it will no longer have the green tint and will look normal. The green tones from freshly sawn logs will be lost once the boards are exposed to air (and drying) for a period of time. As Gene mentioned, microwave drying is too short of an exposure to the air for the green to be lost, so be a little more patient. However, different walnut logs can produce dried lumber that will be either lighter or darker in the brown tones due to differences in each log.

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