Defects in metals and alloys are at the heart of metallurgical behaviour. We can picture the order of atoms and some of these defects using a stack of metal balls in a box. Here, we see a partially ordered polycrystalline material, with defects, grain boundaries and crystal twinning. Scientists use microscopy and X-ray diffraction to distinguish deformed crystals from the recrystallized crystals (here the diffraction images of aluminium cans). Source: Voyage dans le cristal.