Earrings with hollowed-out nature casts of oak galls. White gold and painted gold ornaments. Oak galls are plant growths caused by gall wasps when they lay their eggs in oak tissue, manipulating the tree's growth hormones. Their shape and texture vary depending on the wasp species and the tree’s reaction. The galls cast here come from an English oak (Quercus robur) in the Rhine floodplains near Karlsruhe, where they were torn off by a storm. Ground oak galls served as a key ingredient in oak gall ink, which was the most widely used ink in Europe, the Mediterranean, and later America from the 5th to the early 20th century. The vast majority of manuscripts and still existing documents from this period were written with it.