A bowl my Dad made from a limb of the tree that held my childhood treehouse. He told us that the wood had been spalted for 5 years, I hadn’t heard of that process and he explained that it was what was caused the black marbling in the maple. Basically the wood is kept from drying out and it’s colonized by fungi that cause the dark lines. Interestingly, the fungus does not weaken the wood: From Wikipedia:
Also known as sapstain, or in its most common form, bluestain, this type of spalting occurs when the darkly-pigmented fungal hyphae grow in the sapwood parenchyma of a tree. A visible color change can be seen if enough hyphae are concentrated in an area. These pigmentation fungi often colonize wood via the rays, but are not considered decay fungi due to their non-destructive use of easily available wood carbohydrates. The most common groups of pigmentation fungi are the imperfect fungi and the Ascomycetes. Mold fungi, such as Trichoderma spp., are not considered to be spalting fungi, as their hyphae do not colonize the wood internally.
While pigmentation fungi do not degrade the wood cell wall, this type of decay can lead to a reduction in toughness (amount of energy absorbed before breaking), and increased permeability. Pigmentation can occur on both hardwood and softwood, unlike other types of spalting which are more host specific.
The maple tree in question was struck by lightning a few years ago and is much diminished, but is still strong and each time I see this bowl I will think of the summer days I spent in it’s limbs reading Heinlein and Asimov. <3