The only thing I know what to do with black socks is singing the girl scout song.
"Black socks, they never get dirty. The longer you wear them, the stronger they get. Sometimes I think I should launder them, something keeps telling me no, no, not yet, not yet, not yet..." Sung in rounds. Ha ha ha.
With my dh's socks, by the time they need to retire, they need to be tossed!