This is a well-known effect on wood to anyone who does restoration using a two-part cleaner/bleach treatment (Te-Ka and Snappy Teak-Nu are two commercially-available examples in the wooden boat world). The first part of the treatment is a base (like sodium hydroxide, also known as lye), and the second part is an acid that neutralizes the base. On old wood like a canoe hull, the base turns the wood extremely dark but neutralization lightens it back up, leaving beautiful wood. Fortunately the darkening effect is not nearly so dramatic on new wood, as shown in Rob's photos. People in our wooden canoe community use sodium hydroxide to "age" new wood for replacement parts on old canoes, and it turns out well. A great recent example is the courting canoe that the Norumbega chapter restored for Assembly 2023 - some of its replacement parts were treated with lye to darken them.
Another chemical that does the same thing but can give a different tone to the wood is potassium dichromate. This has been used in woodworking circles for a long time, and it produces a particularly gorgeous effect on mahogany. Unfortunately it is both toxic and carcinogenic, so lye is a much better option for health reasons.
For white oak in particular, woodworkers often darken it with fumes of ammonia or ammonium. I haven't tried fuming on other species. The best thing about all of these chemical treatments is that they don't "muddy up" the wood like stains, especially filler stains, can. As seen in Rob's photos, the effect is clean and much more even than with stains.
