As handcrafting is a time-consuming process, only a limited number of unique knives can be produced in the course of a lifetime. This uniqueness is enhanced when precious materials are used such as gemstones, animal teeth, and fossils, some of which are so rare that they may no longer be obtainable. Creating truly magnificent pieces, meanwhile, requires the cooperation of experts in other arts such as engravers, who imbue the work with even greater rarity. The combination of these factors means that knives can have tremendous value as display pieces as well as be sound investments.