When we built our house, they used, "character oak" flooring. But the spiral staircase company couldn't make treads with the same character. They were willing to use nice oak for 22 treads and 2 landings for $3500 which offended my sensibilities. So off I went on a hunt for some 5/4" wood that was sufficiently diseased. After much hunting, I found a mom and pop sawmill in central Virginia (I'm in the DC area) that had some rotting log out back.
stair treads.jpg
I'm finishing up the last 5 treads and second landing this weekend. I've used a lot of epoxy to fill worm holes and stuff. A lot of the holes go all the way through so I cheat a bit and drill from the back and fill the underside with a dowel rod. It takes less epoxy that way. It takes several sessions with the epoxy so it's pretty much an all day affair, off and on, to fill and wait and fill and wait.
My wife called the treads, "Stunning." That's all the complement I need. I saw to it that the treads were installed according to their visibility by her. The last five go at the bottom of the stairs to my shop and the landing is for my office so I'm well into the home stretch. Yay! One more project down.