Signs of corrosion under the paint
The Mikasa was ravaged by weather several times. First it sank when the magazine exploded in Sasebo harbor ironically on 9/11/1905. It sat on the bottom for 11 months until it could be refloated. It was also stripped by the US forces after WWII as part of the dmilitarization of Japan, despite the fact that the boat was surrounded by dirt and could not move. The superstructure you see today is a replica made in a joint effort of the US Navy and the Japanese Maritime Self Defense Forces (i.e. Navy)