noun
oyster shell lime
Lime made by burning oyster shells; used historically in plaster, mortar, and as a whitewash.
昔の日本建築では、壁に牡蠣灰が使われていた。
In old Japanese architecture, oyster shell lime was used for walls.
Compound of 牡蠣 (かき, 'oyster') and 灰 (ばい, 'ash, lime'). The reading ばい for 灰 is a specialized term for lime or ash used in construction.