Metal Stain in a log direction

[WV Sawmiller]

   Member GAB and his lovely bride just left but before they did one thing we were discussing were the dark blue or black stains in logs that generally indicate the presence of metal (Nails or an old fence and such) in the log. A question we had is

1) does the stain go in both directions above and below the metal or
2) does it just go up or
3) does it just go down

    I had always assumed it spread in both directions but if anybody is more familiar with the physics of a log and knows the correct answer please post it here. This could be very helpful information when we are sawing and get lucky enough to see such a stain before we hear that distinctive "ding" and watch the blade heading south or north as the case may be.

   Any information you have about this would be very welcome. Thanks.

[Jeff]

Having hit iron in hundreds of hardwood logs in my sawing career, and having a more optimum view of the cut faces due to the face of the cut passing vertically in front of me free of sawdust, I can answer that question. The stain moves both up and down the tree in what I would say on the average, equal amounts from the object. It also moves across thr grain, but that is more  limited due to what, i can't say.

[Tom the Sawyer]

My experience is different, but I almost exclusively deal with hardwood logs.  Stain runs down from the metal and spreads slightly round the actual object, especially with walnut and oak.  If you find stain on both ends of the log, that means there was metal above the upper end of the log.  That does not mean that there isn't metal in the bottom log (very common in trees that were used for tree stands). 

If on the bottom end and not the top end, there is metal in the log - just don't know where; although the position on the end of the log tell you which quarter it will be in.  Some species are less reactive to the presence of metal and plated metals may not stain, nor will recently added metal.  I have also milled logs where the metal wasn't an issue, having been there and caused the stain, and then corroded away so that there wasn't anything to hit - that is rare though.

[Ron Wenrich]

I found it to move further down more than it does moving up.  Tom's description of what show's on the end is pretty accurate, especially for oak.  Probably has to do with the tannins in oak.  We had plenty of logs that cleaned up right after 3-4 foot being cut off.  It also depends on the metal.  Galvanized material like eye bolts and lag bolts won't show any stain. 

Tulip poplar, ash, and maple didn't have the same metal staining problems.  I hit some RR spikes in a tulip poplar that someone put up probably for hunting.  There was no stain in the logs. 

[Jeff]

My experience is with red oak grown on good sites. This is some of the best red oak area around.

[nativewolf]

Jeff,

Spoiled huh... :D

[moodnacreek]

More confusing is black stain in logs that have no metal. Also blue stains in spruce that means nothing. You really need a metal detector.

[drobertson]

our rule of thumb has been to fall off fire wood lengths until the stain is gone, then hope for the best.

[bandmiller2]

Sometimes you run across false blue from the saw chain or the bar that made the cut. Any sign of blue is grounds to pull out the detector. Frank C.