I made two in the 90's with gorgeous desert ironwood for guys that actually used their knives. In a couple of years, they both turned so dark that you could hardly see the grain. They were easy to restore. I rubbed them down with a 3000 grit 3M automotive pad, then 3M 4000 and 6000 grit polishing paper, and the original look came back. After a while, though, they started to get dark again. It seems like they oxidize and it's accelerated by sunlight. I'm not sure what to do to prevent that.