Charles Bragg (no, dammit, not the painter)
schreef
I have what was sold as Honduran mahogany and it looks like it
to me. What is bothersome is that parts of my boards refuse to be
smooth..... I can sand (to 220, which is what I read is the max
useful for mahogany) or scrape as much as I want and still there are
these parts, typically an inch wide and between 6-12 inches long, that
remain fuzzy. They don't "tear out" so much as just look fuzzy. A few
months after finishing them with oil and shellac, those parts look as
if they have sucked up all the finish and some are beginning to
lighten up - a blond streak in brown hair, so to speak.

So, it this the behavior of some wood other than HM? Or is it
sapwood? Or is it my bad finishing technique? ?? ??

+ + +
I can't say.
- as to if this is mahogany, who can tell from just a few words?
- there is a phenomenon called reaction wood, which will do weird things,
but I cannot say I ever heard this being a problem in mahogany. Crotch
pieces should have plenty of reaction wood and these obviously can be
finished just fine.
- it is not sapwood, since this would have a different color
- it should not be interlocked grain, since although this will cause tearout
it can sanded quite smooth (may take a long time in bad cases). Note that
scraping would not do it, since the streak would have to be scraped in the
opposite direction from the surrounding wood). If is interlocked grain then
sanding thoroughly and refinishing (or just refinishing) should solve it.

My guess would be badly interlocked grain, since this will locally behave
like end grain, but it is a guess only.
PvR