Blue-Green Streaks in Sawn Oak
A discussion of various factors that can cause discoloring streaks in sawn lumber. January 17, 2011
Question
I had a red oak log sawn about one year ago and we noticed some blue/green streaks in the wood. It was almost like it had been dyed. It went from the stump end up about 5ft or so. It was very strange and real hard to sand out - in some cases, it couldn't be sanded out. Does anyone know what causes this?
Forum Responses
(Sawing and Drying Forum)
From contributor D:
Black spots/streak in both the log and stump wood is an indicator of possible iron in the wood, nails and such. Wondering about copper, in your case?
From contributor S:
In grade lumber this (if not caused by hardware) is referred to as mineral. This I believe is caused by absorption of certain minerals (including iron) directly from the soil on which it grew.
From contributor P:
If sanding worked at all, this likely was a surface stain. Most likely a fungus while drying from improper ventilation.
From contributor O:
In CO the beetles are killing off the pine trees. The locals there are making stuff out of beetle kill pine which has blue green streaks.
From contributor B:
Nails and fence wire will do this and also kill the saw blade.
From contributor U:
I had a piece of red oak with stains like that in it. When I gave it the first pass through the planer I saw shiny stuff. Turns out there were 7 9mm bullets in the board. The guy who did it must have either been standing right next to the tree, or was a helluva shot - the grouping was under 3 inches.
From Professor Gene Wengert, forum technical advisor:
The greenish color is indicative of fungal or viral staining, almost always called mineral. The iron tannate stain is not greenish, but is blue or black. The streaks are often associated with grubs or beetles entering the tree.
From the original questioner:
Thanks for the input. The streaks were probably more blue than green. In my case there were no nails or metal in the log whatsoever - it was in a couple different spots in the log. The tree growing on a creek bank was the only log I have ever run across like that so far.
