Hopefuly the item is completely sealed by concretion, with no air leaks. Exposure to oxygen is another issue. Immersion in water tanks is a must; Cook's 'Endeavor' cannons were carried to the mainland in tanks filled with sea water. Then followed a series of treatments; electrolytic reduction, distilled water washing, wax impregnation, heat treatment, caustic soda bath ... you name it.
Easy to assume that often iron artifacts lose their chance to be recovered from the bottom of the sea, in opposition to those in bronze; specially considering that this kind of findings is due to freelancers, lacking the means or not whilling to handle such complexities.
It is estimated that there are circa ten thousand shipwrecks in all the (tiny) Portuguese coast. I am still waiting, for a few years now, for the nearby city authorities to decide recovering half dozen cannons (mostly culverins) from the sea, closest from the shore, from a 1600's shipwreck. The excuse is the sea conditions.
|