However, I've come to prefer tool steel because it does a number of things that the others don't. First, because it will rust and stain, it will gradually blue over the years. This is rather like a fine wood gunstock aging and darkening, and is very handsome. Look at a well-cared-for butcher knife some time to see what this is like. Second, a skilled smith can forge tool steel to a differential heat treat—a very hard edge and a softer, more flexible spine, which gives you both a superior edge and considerable blade strength. Japanese swordsmiths make katanas and wakazashis this way, and accentuate the temper line, which is called a hamon. Lamont Coombs has made a couple of hunting knives for me that incorporate a hamon, and it is cool to the nth degree.