續一切經音義 5.165

5.165

樺皮（上華化反或作樺切韻山中木名也多出陰山其皮赤白二色白者為上西域用書梵夾也）。

Birch bark [樺皮] (The first character has the fanqie phonetic spelling 華 + 化, or written as 樺; the Qieyun says it is the name of a mountain tree; it grows mostly on Mount Yin; its bark has two colors, red and white, the white being superior; in the Western Regions it is used for writing pothi manuscripts).