I've always (well, not always, but for about ten years now) thought that the the finish of the pipe is purely a question of economics. No sane pipemaker will rusticate a well grained, flaw-free stummel because it will fetch a higher price as smooth. Good briar is not cheap, and if all the blocks with visual flaws would be cast away, I imagine the price of briar pipes in general would rise steeply.
This example is of factory made pipes, but I think the basic the same briar economics pertain to artisan pipe makers as well. Pricing is from more expensive to less expensive:
- ]If the stummel has a nice grain and no visible flaws it will become a smooth pipe. Typically: nicer the grain, the lighter the stain. (1.)
- If the stummel has a nice grain, but has sand pits and/or other flaws it will be sandblasted as this removes the flaws (often in the softer part of the briar) but exposes the grain. Again, if the blasted finish is free of visual flaws it will most likely get a lighter colour finish than a piece that does have blemishes.
- If the stummel has no real grain, or is partly bald, there's no point sandblasting it, and will be rusticated. This can be anything from a five minute dremel job, to intricate and imaginative carvings.
Fun thing is that pipe smokers have differing preferences. Some like blasted, some craved, and some prefer a smooth finish. Some like all.
(1). Some lower tier pipes get their sandpits and filled with putty and finished with dark coloured stain/lacquer to further cover them. They will be revealed sooner or later. These pipes do not age well.