1911 Encyclopædia Britannica, Volume 14… (1911)
“ The finest isinglass, which comes from the Russian ports of Astrakhan and Taganrog, is prepared by steeping the sounds in hot water in order to remove mucus, &c.; they are then cut open and the inner membrane exposed to the air; after drying, the outer membrane is removed by rubbing and beating. As imported, isinglass is usually too tough and hard to be directly used. ”
