I've been trying to find out about cherry darkening - mainly because I built some nightstands out of cherry and finished them with only polyurethane (no stain), but they don't seem to be darkening much. It's been hard to really find out what makes cherry darken to I set up a test.
The experiment: Take a strip of cherry and cut it into four pieces; divide each piece into three sections and put nothing, water-based poly, and oil-based poly on the sections, respectively; also, cover a small portion of each section with tape. Put one piece in sunlight, one in darkness, one under incandescent light, and one under fluorescent light.
So far, after only 3 days the pieces in the sunlight, incandescent light, and fluorescent light showed noticeable darking (compared to the taped over areas) on the natural and water-based poly sections, but showed no noticeable darkening on the oil-based poly section. The piece kept in the dark showed no darkening on any section yet.
I'm wondering if the oil-based poly is preventing any darkening so far because of blocking more light or air compared to the water-based poly. I also wonder if the oil-based poly could still be curing and "stealing" oxygen for curing that might otherwise pass through to the wood. I'm really hoping the oil-based sections eventually darken otherwise I'll be disappointed thinking my nightstands will never get darker.
Charles Lerner