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MINERAL STAIN

The term "mineral stain" was given, apparently, because of a mistake belief that the cause of the phenomenon was minerals brought up into a tree from the soil through the sap. This is NOT necessarily correct. Sometimes that's the cause but often as not, the cause is not actually understood. There are two forms of this phenomenon that I am familiar with. In the first form, the stain runs up/down the tree and spreads out only slightly, producing long stains in the wood. These are generally olive-green to dark brown. In the second form, the stain spreads out in all directions and produces a less emphatic but much larger area of stain, usually gray but sometimes a mottled brown. Both of these forms are very common in maple and the second is also common in poplar. I've seen this mentioned with hickory and basswood but I haven't worked with either, so maple and poplar are the only two in which I have encountered it. It is my understanding that the gray stain often found in maple really IS caused by minerals.

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Examples:


"rainbow" (mineral stained) poplar. This is the most colorful form of mineral staining I know of)


various pieces of poplar with mineral stain


bird's eye maple


various pieces of hard maple with mineral stain


pieces of red maple with mineral stain


apple with both mineral stain and white rot


cherry


small piece of osage orange with mineral stain


box elder with mineral stain


box elder bowl with very heavy mineral stain