Final answer:
A vitreous coating applied by fusion to the surface of metal, glass, or pottery is known as enamel, a process involving the fusion of colored glass powder to the surface through high-temperature firing.
Step-by-step explanation:
The vitreous coating applied by fusion to the surface of metal, glass, or pottery is known as enamel. Enamel involves the use of colored glass in powdered form that is bonded to a surface, usually metal, by firing at high temperatures. This material fuse and adheres to the surface when heat is applied, creating a durable and often colorful coating. Not to be confused with glazes used in ceramics, which are typically silicate-based and create a glassy layer on pottery, or with epoxy and polyurethane which are polymer-based paints used in various industrial and artistic applications.