Tech companies are painting data centers with gray coatings on top of gray concrete and steel to resist fire, rust and static electricity. That has made data centers a fast-growing market for paint makers.

In the spring of 2019, workers dredging gravel at Deinham, a site on the Danube in Upper Austria, kept snagging strange double-pointed iron objects in the excavator’s bucket. Instead of tossing them into the scrap pile — the usual fate of corroded iron pulled from riverbeds, since it rarely looks as recognizable as bronze — […]