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Originally Posted by Pusaka
It is quite strange that it should float on water even if it were spongy, and then why should it be spongy? Acid would waste the blade away unless the alloy was composed of two metals one which is dissolved by acid whilst the other resistant.
Wire wool scrubbing pads are as spongy as you can get yet they dont float on water.
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No, wire wool is not spongy. Spongy means there are many micro cavities inside. When you carefully put it on water, then some air might get trapped in these micro-cavities and make it float. And considering that these cavities are of microscopic dimmensions, it might even be difficult for the water to get in.
Normally kerises are made of diferent alloys of iron, some more, some less resistant to acid attack. Yet, it wouldn't be the different alloys that may cause this phenomenon, but the intrinsic structure of iron. Iron is formed by a matrix of microcristals of Ferrite and Cementite. Ferrite is a high iron phase, while Cementite being a low iron border material between metal and ceramic. What I suspect it happened with this Keris is that the Ferrite was dissolved by the acid and left the cementite matrix intact.... more or less.