Hi R.C. Great to see you here again on the forums. As for mahogany, Rob Stevens recently posted about using lye (sodium hydroxide) to darken new wood. It certainly works as you probably know if you've ever used the two-part track cleaner/bleach solutions (part 1 is a strong base like sodium hydroxide or potassium hydroxide). My experience with these makes me worry about leaving such a strong base on the wood un-neutralized. And neutralizing, which is what part 2, an acid, of the 2-part system does. Neutralizing returns the wood to a nice bright color. One possibility is the use of potassium dichromate. It makes new mahogany look spectacular - dark and rich, in my experience a beautiful match for old mahogany. Potassium dichromate is a carcinogen, however, so it must be used with care for the user and the environment. If you do use it, just make a saturated or near-saturated solution in water, which is bright orange, and simply brush it onto the wood. After about 10-30 minutes, rinse in fresh water. The color is extremely stable - I've got mahogany in boats that was treated this way 10-20 years ago and it still looks the same.
Attached here is a photo of a 1922 mahogany thwart with one coat of 1:1 thinned varnish on it to show color, along with two new replica Central American mahogany thwarts.
The second photo is of those two thwarts after applying potassium dichromate, letting it sit for 15 minutes, then rinsing with water. They are still wet in the photo.
Now that they all have been varnished (maybe 6 coats; no photo yet), the old and the new thwarts are indistinguishable.
By the way, I've never tried leaving sodium or potassium hydroxide on wood to see what happens in the long run. Does the wood degrade in any way or is it fine over time? Does the color fade or does it seem stable? Does varnishing have any effect - does varnish adhere well; does it change the color? I don't know, but perhaps Rob can chime in on this.
Hope this helps,
Michael