Oak Apples are one of nature's little tricks. Oak Galls Wasps are small, non-stinging wasps that lay their eggs on the leaves and branches of oak trees. The oak tree, in turn, treats these eggs as an infection, creating a gall around the egg as shown above. The egg larvae feeds off the gall tissue during its gestation and, when matured, burrows its way out of the gall to continue the cycle. The left over galls are full of tannins, which have been used for centuries for their use in pigments and ink. In fact, one of the oldest blank ink recipes in the world is a mixture of oak galls, iron, and a binding agent like gum arabic.

They are still used today in many natural dye recipes for their ability to help bind mordants and natural pigments to natural fibers.