I have been curious about them, but in a rather different way. Like
@Marek07 said, the steel comes from reclaimed car & truck leaf spring.
If I go back far enough on their Facebook page, I can find paragraphs (in Vietnamese) claiming that these knives are made from (iirc) Soviet tank parts and rails leftover from the war. Obviously, to me Soviet tank sounds (a) "cool" and (b) not food safe.
Since I know nothing about metallurgy, I want to know how one can tell if these knives are made from steel that aren't contaminated with, say, lead, or radiation?
Before you say I'm paranoid, I'm really not. I understand how non-existent food safety and all other standards are there - I get food poisoning every time I visit. And I don't think the blacksmiths are willingly using "contaminated" steel either - they might genuinely not know. Question is, how do we?