This article reexamines Germaine Krull's seminal 1928 photo book Métal, tracing the implications of the speculative analogy drawn by the project between metal and photography. Following this analogy through nineteenth- and early-twentieth-century architectural discourse, it newly situates the photographer's investigation against Sigfried Giedion's contemporaneous theorizations of iron construction and modern photography. Rather than critiquing or celebrating industry, Krull focuses on metal as it manifests the peculiar and fraught experience of living amid large-scale technical systems. In a singular way, Métal mobilizes its driving analogy to invoke—and, moreover, to theorize photographically—the infrastructures organizing Western European modernity.