https://phys.org/news/2018-11-olive-oil-fungus-wood.html

Elke van Nieuwenhuijzen has now thoroughly investigated the natural fungal composition of these layers. She was supervised by, among others, mycologists from the Westerdijk Fungal Biodiversity Institute in Utrecht. Outdoors, she impregnated planks of three types of wood (spruce, pine, ilomba) with three types of oil (olive oil, crude linseed oil, stand oil). The fungi then formed automatically, and on some planks, formed an opaque black layer. She did the same experiment in Norway.

Olive oil worked best in the Netherlands, producing an opaque black protective layer for all three types of wood. Crude linseed oil on pine also worked well. In Norway, the picture was broadly the same, but it took longer for the layer to fully cover the planks. Van Nieuwenhuijzen suspects that this is because of the colder climate.