Making Glass to Create Beautiful Beads
Glass has been around for thousands of years, but before people learned how to manipulate it, nature was the world’s only glass maker. Erupting volcanoes would melt rocks and sand into beautiful, natural glass sculptures. Lightning would strike sand and create long, thin tubes of glass.
Human’s ability to make glass developed over a long time, but the ingredients haven’t really changed. Basic ingredients include sand (the chief ingredient), soda ash (an alkali that lowers the melting temperature of sand), and a stabilizer, usually lime (which keeps the glass from crumbling). Kathy Seamands of CiM Glass says once all the ingredients are together they are heated to 2400°F, “The very first batch always contains the basic raw chemicals. Subsequent batches add cullet (scraps of glass) from previous melts of the same formula to the mix. Then the batch and cullet are added to the furnace. This is called charging the furnace. The glass melts in the furnace for a specific length of time before it is ready to pull.”
The melting time depends on several factors, including whether the glass is transparent or opaque and what color it will be. The time can vary between 12 and 18 hours. Beth Hylen of the Corning Museum of Glass says, “Glass is a rigid material formed by heating a mixture of dry materials to a viscous state, then cooling the ingredients fast enough to prevent a regular crystalline structure.
As the glass cools, the atoms become locked in a disordered state like a liquid before they can form into the perfect crystal arrangement of a solid. Being neither a liquid nor a solid, but sharing the qualities of both, glass is its own state of matter.”
Kathy says the first batch generates the cullet, “The second and subsequent times we melt, each melt is a mix of cullet and raw materials. The cullet and batch are thrown into the hot furnace and melted together.” The size of the pot varies from 50 to 200 pounds. Kathy says the quality of China’s furnace pots is not as good as what is found in the US, “The furnace pots usually last a couple of months. Our pots are not retired on purpose – they usually break in the midst of production. If they break with glass in it, all that glass is lost. This is the primary reason why we do not melt more expensive pinks and purples than we do – fear of this loss.”
Glass makers rotate which colors of glass they make in the pots. Kathy says, “Sometimes the next melt can be affected by what was in the pot previously and the color will shift if not washed properly. The order of melting is important. For example, it is difficult to melt clear after a day of intense black.” After each melt, the pots are washed by dipping clear glass in them and swishing the glass around over and over until the pot is clean. Goldstone, however, doesn’t come off easily. It’s the only color that will ruin a pot. Glass makers break the pot to get the goldstone out, and then the goldstone is broken by hand into useable chips. That’s why goldstone is so expensive.
Creating Beautiful Colors
Adding metal oxides creates the colors lampworkers love. Manufacturers add iron to create green glass, copper to make light blue, and gold for rubies. According to Beth, manganese dioxide actually takes color out of glass, “However, in higher amounts, this element can create purple, and in even higher concentrations, glass can appear black.” Manganese was used by early Egyptians when they created their purple glass. Chromium is one of the most useful coloring agents and is used to make dark green. It’s not easily soluble in glass and if not mixed correctly, black specks may form in the finished product. Chromium aventurine is interesting. The formation of chromic oxide, which crystallizes out of the melt, causes a sparkling effect. During the cooling stage, the crystals orient themselves parallel to the glass, which creates the glittering reflections we see.
Once the glass has finished mixing, it’s time to pull it into cane. Surprisingly, many glass manufacturers such as CiM and Lauscha still pull their rods by hand, though the technology exists to mechanize the process. Kathy says, “Pulling by hand is the best way to meet our mission of producing the highest quality 104 glass color rods in the market.” A glassblower takes the glass out of the furnace and creates a gather on the end of a thick rod. He dips and marvers several times in order to get a large gather to pull. Once enough glass is on the rod, another rod is added to the gather. The two blowers then walk away from each other until they have the desired diameter cane. Kathy says, “Our cane pulls are about 40 meters in length. Once pulled, the rods cool on wood slats. We have a woman on our team who squats on a little stool at the end of the pull and uses a tool to pull the cane and clip it on the spot, still warm, into 13-inch lengths.”
Types of Glass
Glass is categorized by its chemical composition and is known by its hardness. The most common manufactured glass is soda lime. It’s the cheapest to make and the least resistant to sudden changes in temperature. This is soft glass.
Leaded glass is a second type of glass. Beth says, “When added to glass, lead makes glass brilliant, resonant, and heavy. Glasses containing a large percentage of lead are known interchangeably as crystal, lead crystal, and lead glass.” It’s similar to soda lime in that lead glass will not hold up well to high temperatures or sudden changes in heat.
A third type of glass is borosilicate and it contains boron. It’s well known for its resistance to thermal shock. Known as hard glass, boro is used in cookware, lab equipment, and lighting. Boro was developed by German glassmaker Otto Schott in the late 1800s in a similar way to soft glass. In the beginning, most boro was colorless, but in 1986 colored boro was introduced to the market. Using silver to color the glass creates beautiful and sometimes surprising results. Because boro is stronger than soda lime glass, it’s used for creating figurines, pipes, marbles, and, of course, beads. Because of its heat resistance, borosilicate glass coated the insulation tiles on the Space Shuttle.
Other types of glass include aluminosilicate glass, 96% silica glass, and fused silica glass. These are more difficult to manufacture, but all can withstand temperatures higher than 1600°F. Beth says, “There are already tens of thousands of workable glass compositions and new ones are being developed every day.”
From the hands of ancient men to the pinnacle of space, glass is a valuable, yet mysterious, entity. Without it, we couldn’t decorate our homes, our churches, or ourselves.