How is the motion of an interface between two solid crystals related to its shape?  This is a question that was impossible to address in the past because we were not able to see within solids.  Using X-rays, it is now possible to maps out the positions and shapes of crystals within solids.  We have used this information to measure the detailed shape (curvature) of internal interfaces and correlate it to the orientations of the crystals.  What is particularly new and interesting here is that when the interfaces are classified by their type (defined by crystal orientation) there is a strong relationship between the type of interface and its curvature. This finding is important for predicting the motion of these interfaces during materials processing.  If we can use this to learn how to predict the motion of these interfaces, it may be possible to develop improved structural materials that are stronger and weigh less.