Knife collectors usually specialize in a single type. In the 1960s, the United States government passed a law that required knife manufacturers to mark their knives with the country of origin. This seemed to encourage the collectors, and knife collecting became an interest of a large group of people. Early bone-handle knives had steel blades and pistol-shaped handles. About the mid-nineteenth century, the modern knife became popular. All types of knives are collected, from top quality twentieth-century examples to old bone- or pearl-handled knives in excellent condition.