I see some maple necks with brownish streaks sometimes going with the grain and sometimes not. Are they mineral streaks? How does this happen to the wood? Is it considered a defect? Thanks!

It's only a "defect" cosmetically to those who want pure, unmarked maple sapwood. Some prefer a bit of character. There's more than one cause of dark streaks in maple so got a pic of exactly the type of marking you mean? Some marks are cause by a small fly laying eggs between the bark and cambium layer which results in small random scarring not unlike spaghetti when abundant. This is call fly spec in maple and glass worm in swamp ash.

Hi Larry thanks for the reply. I tried to capture a picture but it could be hard to see. This picture shows a larger streak not following the grain and other small ones near the bottom that appear to lie right along the grain.

Doesn't look like the scars formed from fly larvae, but "regular" mineral streaks..if "regular" is a proper term since nothing is written in stone with wood. These streaks are only cosmetic and one shouldn't be concerned otherwise. It can be frustrating to mill a beautiful clean maple neck piece then discover mineral stains inside tht won't carve out. This is part of the high cost of custom milled neck blanks.

Here's one explanation for mineral stains WITH theories:

Found this in TEXTBOOK OF WOOD TECHNOLOGY by Panshin & DeZeeuw, pg. 327

"Natural and Chemical Stains
1. Mineral Stains. This term has been loosely used in the trade to denote
stains of various kinds in lumber without regard to their origin. In a more
restricted sense, the expression mineral streaks or mineral stain should refer to
the olive and greenish black, usually lenticular, areas common in otherwise normal
wood of hard maple and occasionally also in other hardwoods. This discoloration is
traceable to dark globular masses of the material responsible for the color, found
mainly in the ray cells and in the vessels. These extraneous materials are
apparently responsible for the higher mineral content of such areas compared with
that of the surrounding wood, averaging 5.2 % ash content in hard maple, as
contrasted with only 1.2% in normal bright wood. When wood containing mineral
streaks is seasoned, cracks frequently form where the discoloration is deepest.
Millmen contend that wood with mineral streaks is harder than normal stock and that
is has a pronounced dulling effect on cutting tools. The discoloration caused by
mineral stain are also considered objectionable because of the problems such local
stains present in wood finishing.
No acceptable explanation has yet been found to account for the development of
mineral streaks. There is some evidence that the mineral discoloration may be
initiated by obscure injuries, which in some manner interfere with the normal
physiological functioning of the cells proximate to such areas. Likewise, a
possibility of bacterial infection as a contributing cause to formation of mineral
stains cannot be dismissed."

They also went on to say about extraneous material in the cell wall. "When the ash
content is above normal, silica may often be the principal component; however, a
notable exception occurs in the mineral streaks of hard maple which are unusually
high in manganese."

I see streaks like that all the time and have often wondered what they are. Great info thanks again Larry! :bassist: