"It’s not. Silver’s not worth that much. A Sung Dynasty vase, cleaned up, can go for more than its weight in gold. Gold. And it’s easier to find the vase—you just scan the seafloor, looking for something shaped like a junk. A sunken junk makes a distinctive image on sonar. Whereas an old crate, all busted up and covered with coral and barnacles, tends to look like a rock."