PROBLEM: An otherwise perfect board has a knothole. How can I best fill it without detracting from the beauty of the board?
If you want to conceal the knothole, look for an area on a scrap piece of wood where the grain forms circles or has a pleasing irregular shape that will blend with the wood around the knothole. You might even find a tight knot in a similar piece of wood. If you just want to fill the hole without concealing it, choose a very dark piece of scrap that resembles the color of the missing knot. Saw and file a plug that fits well at the surface. The fit won’t be perfect in any case, but the surface fit is the most important. The trick is to glue in the plug with a filler made from sanding dust and epoxy glue. The epoxy will glue the plug in place, while the sanding dust will fill any imperfections. Of course, if you have the missing knot, you can just glue it in with the epoxy filler.