Enamel is glass on metal.  It is an ancient art, used to make precious objects from miniature 
portraits to Faberge eggs.  Cartier used enamel to great effect particularly in the 1930s, as did

I work in enamel to make jewelry as well as objects and art for walls.

TOP ROW:'Kachinas' necklace, close up.Cloisonne enamel on silver, coral and turquoise beads, $495.'Sonia Delauney Necklace, cloisonne enamel on silver, leather cord, $165.Enamel pin, enamel on silver.Can be made to order, $165.
SECOND ROW:'Absolut' champleve tiled enamel painting, 8 1/2" x 11".'Postcard' 
charms, on silver or gold-filled chains (chains not shown), $125 each.'India' 
postcard charm.THIRD ROW:  'Singapore' postcard charm, $125.'Kachina' necklace showing coral and turquoise beads.'Posters' wall painting, 5" x 7", enamel on copper.