Say there's an in-universe weapon so odd looking that it is rumored to have been stained by the blood of a "holy" mortal, so much so that no amount of water can wash it away.

Is there a chance human blood can stain metal through time, or is there a metal that could give off this impression to befit the rumors better?

Edit: I realize I was being confusing: No magic is involved, it's simply a rumor to discourage regicides of "God-chosen" monarch.

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    $\begingroup$ given that enough water will dissolve most steels and iron, the answer would be a hard no. $\endgroup$ – John May 13 at 16:28
  • $\begingroup$ This needs a bit more clarification. What is the weapon made of? Is there anything unique about the victim's blood? Does the stain need to resemble blood, or will any discolouration do? $\endgroup$ – rek May 13 at 16:50


A stain is defined as 'color by applying a penetrative dye or chemical'. And blood is a chemical - actually, it's a lot of them, but it is a chemical. Now, let's say you apply blood to a sword - it will rust. And rust is a color which is different from normal iron and not only that but it is granted by applying a chemical. Furthermore, if blood is only applied to part of the sword and not cleaned off, only that part of the sword will rust. Additionally, while rust isn't irreversible, as long as it's only exposed to normal air and water, the rust will not revert. So, yes, a metal could be indefinitely stained by human blood, 'stain' in this context meaning 'rusted'.

Just be careful trying to wash that rust off. Wouldn't want to turn the rest of the sword rusty.

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To make a permanent stain you need to have something that reacts with the blood to form a compound that is not water soluble.

I think one option is to aim to something reacting with the iron contained in the hemoglobin, to give some substance that adheres to the weapon, but out of my mind I cannot remember any of such reactions.

Another option would be a magnesium blade, where the magnesium would react with the water contained in the blood to make magnesium oxide, which is almost insoluble in water. While magnesium is gray-silver, magnesium oxide is white.

However mind that magnesium is highly reactive, so it would be a poor idea to wash it with water or to expose it to fire. There is a reason why the first flashes were made with magnesium powder or whiskers.

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  • $\begingroup$ The challenge here is to find something which would be stained by one person's blood and not anothers. Does your holy warrior have highly unusual blood chemistry? $\endgroup$ – David Hambling May 13 at 16:34

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