Tung Oil

Tung oil or China wood oil is a drying oil obtained by pressing the seed from the nut of the tung tree (Vernicia fordii). Tung oil hardens upon exposure to air (through polymerization), and the resulting coating is transparent and has a deep, almost wet look. Used mostly for finishing / protecting wood, after numerous coats the finish can even look plastic-like. Related drying oils include linseedsafflowerpoppy and soybean oils.[1]

Wikipedia.org, accessed on 28 June 2019

Tung oil is applied to wood handles, such as on knives or other tools, to preserve the wood.