The golden dolphins were formed over a roughly carved block of wood over which lead sheets were applied. Copper was placed over the lead, before the application of the final layer of gold which was acquired from pounding gold coins into sheets.
The two golden dolphins are male and female, and slightly different in size. The core of the golden dolphins are composed of hinoki cypress.
Used to adorn the main ridge of castle roofs, they are a symbol of the feudal lord’s authority. — Nagoya Castle museum billboard