“Smalti” comes from Italian, and refers to a paste or glaze made up of silica melted with sodium or potassium carbonate. Metals are added as stabilizing agents, as well as metal oxides (for color). The paste is fired at high temperatures, then rolled out into a pancake-like slab that can be up to 6 inches thick. Once cooled, the slab is traditionally hand-cut into small rectangular pieces of tile.
Artisans typically turn the resulting tiles (also called tessarae) on their sides, as this exposes swirls or layers of colorful textures.
Smalti tiles are typically colorful, textured, small format tiles.
Smalti tiles were originally developed to complement natural marble and granite tile colors. Newer oxides have enabled smalti tile makers to venture into nontraditional looks as well. As a glass tile, Smalti tiles are also weather- and stain-resistant, and are relatively easy to cut. All these features have made the popularity of this type of tile endure among modern mosaic artists and hobbyists as well. The modern “smalto” method has the smelted paste cast in a capsule, rather than rolled out and cut. The capsules, which enable the mass production identically-sized tiles usually produce tiles in the 3⁄4" × 3⁄4;" × 1⁄8" format (i.e. 20mm × 20mm × 3mm).
Translucent Smalti are lightly colored smalti tiles that look like stained glass, except that the colors are uniform throughout the smalti tile. Translucent smalti have glistening surfaces, with the visual depth of translucent glass.
Byzantine Glass is made from thinner slabs of glass, usually about 1⁄2 the thickness of a typical smalti slab. The slab is cut roughly to squares, most pieces being somewhat irregular in shape, about 10mm (3⁄8 inch) in size. Thickness also varies, 4-6mm (3⁄16-1⁄4"). Note that the surface of the slab, not the side, is used as the face of the tile.
As it cools, the surface of a smalti slab undergoes more unpredictable color changes than on the interior of the slab. This, for better or worse, makes for more variations among Byzantine Glass pieces than in other Smalti tiles.
Metallic Smalti describes when a swirl of a copper-bearing mineral is added into the molten glass before it is pressed. On drying the metal appears as a copper-colored streak running through the body of the glass.
Gold Smalti are made by applying a gold leaf, followed by a thin layer of blown glass, against a Smalti slab, and then heating to sandwich the layers together. The tile is subsequently used face up, as in Byzantine glass.
The gold leaf is typically either white gold (which looks silver when applied), 24K yellow gold, or platinum.
Gold leaf has been traditionally associated with transcendental beauty and greatness; these tiles were often applied to religious decorations and murals.