Making Glass Mosaic Jewelry with Smalti

What are smalti?

Smalti (the plural of smalto) are specialized mosaic tesserae made from richly colored glass. Tesserae are the small blocks of stone, ceramics, glass, or other material used in the construction of a mosaic. Originally developed for Byzantine-era mosaics, the glass contains ingredients which allow a large range of colors to be achieved to produce beautiful abstract and figurative designs composed of many tiny pieces.  

What is glass made of?

Glass is made of sand that has been melted at a temperature of 3090 degrees F. Depending on the sand mixture, glass can have a variety of properties. For example, certain elements or chemicals mixed with sand can change the color and opacity of the glass. 

How are smalti made?

Ingredients

Murano smalti glass is made up of…

• 70% silica sand
• 30% soda, lime “fluxes” that allow the glass to melt at a lower temperature and small amounts of oxides and minerals such as:
• Cobalt - for Blue glass
• Gold - Ruby glass
• Selenium - Red and Pink glass
• Iron Chromium Nickel - Violet glass
• Cryolite - White glass
• Manganese -Black glass
• Cadmium - Yellow glass
• Sulfur - Topaz glass
• Copper Oxide - Green glass
• Lead, Arsenic, Fluorine- Opal glass

Mixture

The specific ingredients and combinations of ingredients used in Murano glass are traditional recipes known only to a few. Italian glassmakers have been perfecting the art of making glass for smalti for centuries. The nuance of color and hue, the variants of opacity and brilliance are all taken into consideration. Murano glass would be colorless without the addition of small amounts of minerals, oxides, and chemical derivatives to the base glass powder. 

Melting

The transformation of the mixture from powder to glass happens in the furnace or kiln at a temperature of 1450° Celsius (2642° F). The powder is melted in a crucible or “pot” until it forms a homogeneous liquid.  Bubbles, variations of color and uneven surface give the smalti life and exuberance; the beauty is found in imperfections. 

The molten glass is then poured onto a slab for cooling, and then cut by hand into rectangular pieces.  The pieces are about 1/2 inch or smaller and they aren't perfect rectangles.  They vary in thickness, shape, size and color.  These natural variations in shape and color are exactly what make smalti the perfect mosaic material and allow the artist to create beautifully detailed images.  

Pouring

Each color of molten smalti glass is poured onto a steel slab in small puddles about 3/16” -1/4” in thickness, and cooled. These puddles, or “pizzas” are made in small batches in a rich palette of colors.. The dominant producers of glass pizzas for smalti ( known as “tortillas” in Mexico) are family owned businesses located in Venice, Murano and Spilambergo, Italy as well as Cuernavaca, Mexico. 

Making 24K Gold Smalti 

24 karat gold leaf is covered by a very thin hand-blown piece of crystal and fused into one solid, durable piece of glass in the furnace. Once cooled each gold “plate" is hand-cut and although the gold appears as if it is on the surface of each smalto, it remains protected. 

Mexican vs. Italian smalti

Size

The Italian “pizza” is poured to a thickness of approx. 3/8", the tortilla 1/4”. The Italian smalti glass is poured thick but then hand cut into thinner pieces (resembling a small brick) to expose the inside of the pizza using a hammer and hardie. This inside (cut side) becomes the working surface of the material.

By exposing the inside of the glass, colors are more vibrant, more consistent in size (5/8" long x 3/8" wide) on the visible working side but less consistent in thickness.  Mexican smalti are cut larger into irregular squares (approx. ⅝” x ⅝”) on the visible working side with a fairly consistent  3/16" thickness, more closely resembling a piece of tile. 

Color

For Italian smalti the focus is on the purity, brilliance, and consistency of the colors. To maintain these qualities the smalti melting pots are changed regularly and great care is taken to avoid color cross-contamination. For Mexican smalti, the focus is on creating a painterly look when making the tortilla. Because the glassmakers are looking for mottled colors, smalti "pots" are not changed regularly, and when one color is finished, a new color is mixed and the two begin to blend.  This makes for beautiful color variations in a single batch but difficulty reproducing colors from one batch to the next.

Cutting smalti

To reduce the size or change the shape of a smalto, three cutting methods are most common: nippers, hammer and hardie, or chopping machine. Wheeled nippers are pliers with 2 round carbide blades. The smalto is placed between the blades, the handles are squeezed, causing the glass to fracture. Nippers are easy to use but can tire the hand and forearm muscles. 

A more traditional method is hammer and hardie (a chisel securely fastened in a wood block). The tessera is held on top of the hardie and then tapped gently with the hammer to fracture the glass. This technique takes practice, but is easier on the hands than nippers. Along with chopping machines, which require turning a wheel to apply pressure rather than a hammer,  these are preferred methods for larger projects. To reduce the size of the smalti in my jewelry, I use wheeled nippers. 

Why I use smalti in jewelry making

I use smalti for their fade-proof, vibrant colors and subtle surface variations and bubbles. I also like incorporating a traditional element in my designs that has been used by artists for centuries.  The gold-fused clear glass smalti that I use have a particularly interesting effect when embedded in opaque resin.

How I make jewelry from glass smalti

After cutting the glass smalti into the desired shapes, I place them into sterling bezels I have made beforehand. I create a composition that may also incorporate glass rods or silver designs and sometimes other materials.  Once I have a design that I am pleased with, I hand mix a two-part resin in the desired color, and pour it into the bezel, completely covering the glass. After the resin has cured I grind down each piece gradually from coarse to a very fine polish, exposing my design embedded in its background. A very exciting reveal!

Glass mosaic jewelry using smalti from my collection

Here are three pendants from my collection that demonstrate how I use glass smalti in my jewelry:

Gold Nuggets Pendant

A dazzling grouping of 24k yellow gold-fused Murano glass nuggets shimmers against a handpoured black resin background, contained by a circular silver pendant setting.

Big Square Pendant

Features a richly colored tessera of Murano glass contrasted against a dark canvas of ground resin. The glassmaking process trails tiny marks and bubbles in each shard of glass, meaning no two "paintings" are alike.

Angle to Angle Pendant

Triangles of 24k yellow and white gold-fused Murano glass smalti balance in hand-poured black resin.

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