In article , spaco wrote:
I am very inexperienced at this, but I have made 5 cherry bowls. I
spend more time sanding them than anybody else does, probably. As I am
sanding/polishing them them with pretty fine grits, let's say 600 or so,
the heat from the sanding darkens them a fair amount.

That's called "burning". It's entirely different from the rich red-brown
patina that cherry acquires after a few years of exposure to sunlight.