indigo fermentation scum
Technical term for the scum that forms near the end of the indigo fermentation process. Rare outside of traditional dyeing contexts.
The indigo dyer judges the end of fermentation by looking at the condition of the indigo scum.
Refers to the plant Commelina communis, also known as 露草 (つゆくさ). The name 藍花 is used because the petals were historically used to make a blue dye similar to indigo.
See also: ツユクサ
Asiatic dayflowers were blooming along the roadside.
Compound of 藍 (あい, 'indigo') and 花 (はな, 'flower'), referring to the flower's use in producing indigo dye and, by extension, the scum formed during fermentation.