Before 1945, steel was just steel. Then, nuclear bomb tests contaminated the atmosphere, embedding trace radiation into all newly-smelted metal. Today, when uncontaminated steel is needed for radiation-sensitive instruments (like Geiger counters, particle detectors, or space telescopes), they salvage it from ships that sank before the blasts. It's called low-background steel and it is a rare, coveted material. Now, one man is doing the digital equivalent.
