“Exquisite Rot: Spalted Wood and the Lost Art of Intarsia”, Daniel Elkind2018-05-16 (biology, design, PD Review)⁠:

The technique of intarsia—the fitting together of pieces of intricately cut wood to make often complex images—has produced some of the most awe-inspiring pieces of Renaissance craftsmanship. Daniel Elkind explores the history of this masterful art, and how an added dash of color arose from a most unlikely source: lumber ridden with fungus…painting in wood is in many ways more complicated than painting on wood. Rather than fabricating objects from a single source, the art of intarsia is the art of mosaic, of picking the right tone, of sourcing only properly seasoned lumber from mature trees and adapting materials intended for one context to another. Painting obscures the origins of a given material, whereas intarsia retains the original character of the wood grain—whose knots and whorls are as individual as the islands and deltas of friction ridges that constitute the topography of a fingerprint—while forming a new image. From a distance, the whole appears greater than the sum of its parts; up close, one can appreciate the heterogeneity of the components…

Inspired by the New Testament and uninhibited by Mosaic proscription, craftsmen in the city of Siena began to introduce flora and fauna into their compositions in the 14^th century. Figures and faces became common by the late 15^th century and, by the early 16^th century, intarsiatori in Florence were making use of a wide variety of dyes in addition to natural hardwoods to mimic the full spectrum from the lightest (spindlewood) to medium (walnut) and dark (bog oak)—with the tantalizing exception of an aquamarine color somewhere between green and blue which required treating wood with “copper acetate (verdigris) and copper sulfate (vitriol).”⁸

…Furnishings that featured slivers of griinfaule or “green oak” were especially prized by master cabinetmakers like Bartholomew Weisshaupt and coveted by the elite of the Holy Roman Empire.¹⁰ Breaking open rotting hardwood logs to reveal delicate veins of turquoise and aquamarine, craftsmen discovered that the green in green oak was the result of colonization by the green elf-cup fungus, Chlorociboria aeruginascens, whose tiny teal fruiting bodies grow on felled, barkless conifers and hardwoods like oak and beech across much of Europe, Asia, and North America. Fungal rot usually devalues wood, but green oak happened to fill a lucrative niche in a burgeoning luxury trade, and that made it, for a time at least, as precious as some rare metals. During the reign of Charles V, when the Hapsburgs ruled both Spain and Germany, a lively trade in these intarsia pieces sprang up between the two countries.