Enamel
A technique for decorating objects with colored glass coatings
Enamel is a technology of applying glass enamel to the surface of a silver object followed by firing. Such decoration is especially popular in jewelry and artistic silver of Europe in the 18th–19th centuries and in Russian art of Fabergé. Colored enamels allow creating bright contrasting ornaments or surprisingly delicate paintings.
The complexity lies in the relationship between metal and glass: enamel requires ideal cleanliness and precise temperature control. Works by enamel masters are valued especially highly.
Amusingly, in the 19th century some failures, when trying to "melt down" silver, overheated the item until it lost its shape, and the precious cup turned into a glass pancake with a silver rim instead of a masterpiece.
Today, enameling is recognizable by the richness of color, durability of the coating, and a special gloss that distinguishes such items at auctions.