How Glassblowing Works

Glassblowing Equipment

To get the beautiful blues and other colors in blown glass, special ingredients can be added to the batch, or melted and fused on later.
To get the beautiful blues and other colors in blown glass, special ingredients can be added to the batch, or melted and fused on later.
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To get things started, let's go over some of the materials you'll need. First on the list? Glass, of course. Most of the glass that you run across on a day-to-day basis is a type of oxide glass, and the base component is silica. Silica (or silicon dioxide) is more commonly known as sand. Glassblowers don't just head to the beach with a bucket though: That sand is too packed with impurities and contaminants. There are certain areas around the world from which glassblowers can get supplies of top-quality sand.

Glassblowers don't use silicon dioxide alone to make glass -- it's got a really high melting point and it becomes very viscous when it melts. So they add other things into the mix to make the glass easier to blow. These might include different metals and metal oxides, like alumina, magnesia, boron oxide and lead oxide, depending on the properties you desire in the finished product.

Let's look at one simple recipe for a common glass known as soda lime glass. Soda lime glass can be used in products like light bulbs, bottles, fiberglass, window panes and lots of other applications. It's generally about 72 percent silica, 15 percent soda (sodium dioxide) and 9 percent lime (calcium oxide). Depending on the product, those amounts -- as well as the remaining 4 percent of the ingredients -- will vary.

Soda and lime are key additives in glassblowing recipes. They're examples of what are known as fluxes; they lower the melting point and increase the viscosity (flow rate) of the glass mixture, as well as strengthen it and make it more stable. Other fluxes include alumina, which can make the glass more durable, and zinc oxide, which can promote a brilliant shine while at the same time helping to keep the glass' molecules from crystallizing (a no-no called devitrification). Barium oxide also helps decrease devitrification and lowers the melting point. Adding lithium will increase the glass' softness, while lowering its melting point and viscosity.

Although lots of products made out of glass are clear, many others are extremely colorful. Those colors come from adding different metal oxides into the glass during the glassblowing process, and they can appear either transparent or opaque. For example, if you put a little cobalt in your melt, you get deep, rich blue, and a dash of chromium makes an emerald green. A pinch of gold will make a beautiful ruby red, but it's a tricky one to add and needs to be done in chloride form. Several additives, like silver, copper and manganese vary in the colors they produce. With silver, the color typically depends on how the silver is added to the melt, but with copper you've got a grab bag of color possibilities that can easily be altered by other metals in the mix and even factors as unpredictable as the atmospheric conditions in the melting chamber.

Starting to sound a little more challenging, right? Now that we've got a better grasp of the materials needed for glassblowing, we're ready to turn up the heat and see how the process works. Go to the next page to dive in and learn how blowing glass typically goes down.