Wiktionary
n. rarefaction
Wikipedia
Rarefication used in the manufacture of guitars is the change of organic, solid woods at low temperatures, typically not exceeding 38 ˚C (100 ˚F), in a chemical-free, vacuum-sealed environment for a prescribed length of time. Impurities are removed from the wood improving the strength of the wood fibers and improving the tone, similar to the natural aging process of tonewoods used by luthiers in guitars.
Tonewoods, typically selected because of stability, include Western Redcedar and Sitka Spruce which are commonly used in guitar soundboards (top woods). These are rarefied to increase stability, and decrease, or minimize, change in cosmetic properties such as the color of the wood. Higher temperatures, such as torrefaction, can change highly valued cosmetic properties in tone woods. Mahogany is also rarefied when used in guitar backs.
Usage examples of "rarefication".
One of the young men was seriously alarmed by bleeding from the lungs, and the intense dryness of the day and the rarefication of the air, at a height of nearly 15,000 feet, made respiration very painful.
His (early) archaeology of actual existence was a neostructuralist reworking of the traditional structuralist's analysis of possible types of experience, but it still placed emphasis on the exterior surfaces and structures of discursive formations and the transformation rules (of rarefication and exclusion) that individuated serious speech acts.