IRON AGE OF SUPERCONDUCTORS .When type-II superconductors are placed in a magnetic field, the flux lines organize themselves into small bundles. When the current flowing through high-temperature superconductors is high enough, these flux lines can move, causing an unwanted voltage drop, a major impediment to the industrial use of these materials. New images of the bundles, produced by Swiss scientists, show that the bundles can entwine into stable "vortex twisters," offering a possible way out of the flux problem. David Nelson of Harvard compares this to the advent of the Iron Age, when smiths strengthened iron by adding dislocation defects through bending. (Nature, 20 Feb.)