Rottenstone and oil on a felt pad (or wad of felt) and elbow grease.
When you do it avoid the temptation to do it in small areas. Make your strokes long and overlapping. It will take longer to see progress but you will not need to spend the rest of your life trying to blend the areas together.
Rottenstone was some place in the back of my little pea brain.
Linseed oil?
Soft, medium or hard felt pad?
Thanks
Linseed oil is fine, or any other, really.
Pad can be anything of felt. I used to use an old chamois shirt piece to do it and it works fine. A chalk eraser is also good and gives a better grip. And since rottenstone is almost chalk you do not even have to worry about cleaning the old chalk out!
