People have always been astounded and fascinated by natural objects or exotica, i.e. natural materials or products such as ivory, minerals, seashells or horn. Working them into precious objects required consummate mastery from artists and craftsmen, and such artefacts were a must-have in any cabinet of curiosities or treasure chamber. Many of these objects are genuine works of art, such as some miniature ivory carvings rich in details that can only be discerned with a magnifying glass. They were elaborately crafted according to the ajour (open-work) technique, with the remaining material’s thickness not exceeding a tenth or a hundredth of a millimetre in some cases. They were referred to as "mirabilia", i.e. marvels of art, created by the human hand.