Information About Opaque Glass

Process

Opaque glass or opaque enamel occurs when bone phosphate or bone ash or barytes (a mineral made of barium sulfate) mixes with the molten compound. To make different tones of blue opaque glass, cobalt oxide, smalt (blue powdered glass) or particular amounts of black oxide derived from copper joins the mixture. Chromium oxides make green, different amounts of iron oxide make either yellow or red, and for ruby, certain amounts of oxide of gold or suboxide of copper changes the color of the opaque glass.

Early Egyptian glass making artists copied precious lapiz, turquoise, rose, cinnabar and emerald stone beads and jewels, becoming proficient in mixing glass to achieve these opaque colors. Exhibits of some of this ancient work from unearthed tombs are in museums.

Customarily, glass tiles are opaque. Developed during the Byzantine Empire (306 B.C. to 1453) these tiles were used for the intricate and beautiful mosaics still seen in museums and European churches today.

Opaque white glass (now called milk glass) appeared around 1470 in Venice, Italy glass maker shops. These early pieces were blue, pink, yellow, brown, black and white. America first produced both milk glass and opalescent milky white (fiery opalescent) glass pieces in the 1830s and continues production in the 21st century. During America's "Gilded Age" (1864-1900) milk glass pieces made for the wealthy reveal a distinct delicacy with beautiful design while milk glass of the Depression era (1930s and 1940s) is noticeably less so.

Murano (an Island near Venice, Italy) glass is the most ancient of fine glassmakers among the Venetian guilds. Venetian glass's fame comes from elaborate, skillfully made and colorful pieces. With management upheavals arising in the 1930s, the opportunity to integrate the use of opaque glass making into the centuries-old Murano quality, proved advantageous for new creative work for this ancient company's artists.