The Hunley comes out of its shell

“A combination of rust, sand, rock and assorted ocean debris, concretions are hard as concrete. The concretion layer that coated the entire submarine, inside and out, was so thick, the original iron has been obscured since the Hunley was first raised from the harbor floor. Some areas of concretion were harder than the iron underneath them. In order for the sodium hydroxide treatment to leech the corrosive salt out of the iron skin effectively, the concretion had to be removed first. In May of 2014, the submarine was immersed in sodium hydroxide for the first time. That initial three-month soak was intended to loosen the concretions.”

http://www.thehistoryblog.com/

(Archaeologists still do not know why the submarine sank.)