A common phenomenon that many kilnformers encounter is devitrification. Devitrification, or devit, is the growth of crystalline structures on the surface of glass. It generally appears as a haze or scum that no amount of cleaning will remove. In this lesson, you will learn the causes of devitrification and ways to prevent it. We’ll also cover ways to deal with unintended devit if it develops. These solutions involve either adding material or removing material before re-firing to achieve the intended finish.