Glass is often thought of as a very stable, unchanging material. That, unless you drop it, it will be around forever. This, however, is far from the truth. Glass undergoes a unique and insidious type of degradation. It interacts with the humidity in the atmosphere, swapping out some of its own components for water, forming a brittle layer that most will recognize as the white scum that forms on glasses that have been run through the dishwasher a few too many times. This degradation, referred to as glass alteration, happens slowly, taking decades if not centuries to be noticeable. For most glass, glass alteration doesn’t really matter – the object is likely to be dropped or lost before anyone notices a change. But for glass objects in museums, some of which have been around for millennia, and all of which are intended to last a lot longer, the slow time scale of alteration can become a problem.