JSeery
Member Emeritus
I worked in a foundry when I was young and all of our cores were sand cores. They are made from a mixture of fine sand and oil, pressed into shape and heated to form a strong but brittle structure that is easy to break after the casting. There is a wax core that is used in something called the lost wax method, but it is fairly rare. I know about it because a collage professor was researching the wax method to try to reconstruct how it was done.