Salt water damage

[Gspragge]

The Hotchkiss projectile and fuze were brought up from a sunken Spanish Warship in the Philippines after
a couple of years (Documented). The damage is frightful and the hardened nose is gone. One might think that would survive better?

The next one is the same kind of projectile and I suspect that the etching is also caused by salt water. It was cased
and the bottom is without damage (I have since cleaned it). If it was in salt water it was either better protected or brought up sooner.

any opinions would be appreciated.

 

[Bellifortis]

The better preserved item may have been lying in slick, so that no oxygen and salt could reach it. Iron items in salt-water are always very badly corroded, while copper and brass are seemingly indifferent. Salt water is very corrosive, especially the more concentrated the salt solution is.

 

[Gspragge]

So the etching on mine is typical under some what protected conditions then (and not for a hundred years etc. but a relatively short time) correct ?

These are both 37mm Elswick Ord. Co. Hotchkiss projectiles contracted to Spain in 1897.
It is essentially identical to the Italian Hotchkiss except for the external fuzing.

 

[thekees]

As long as there is iron or an other lower metal close to the brass or copper (lower galvanic order metal), the iron will corrode away much faster and the brass will not corrode due to galvanic processes, salt water will spin up this proces. Pure brass or copper with no higher (galvanic) metals arround will corrode much slower, even the first layer of corrosion wil shut off the proces, and since there is no galvanic proces it will stop there. Remarkable difference can be seen in old german naval cases or british cases, maybe they did'nt use the same zinc/copper alloy.