That Word, Silica

We’ve all heard of silica (or was that silicon or silicone or silicate? Wait a minute, are there 4 of them!?) And we probably know it has something to do with glass. But what is it exactly?

I have to admit that through the years I haven’t paid much attention to the last few letters of that word and may have used the different terms silica, silicon, silicone, and silicate casually in conversation without knowing just what they meant. But in my job at The Corning Museum of Glass it becomes a little more important for me to be specific since I wouldn’t like to steer our visitors in the wrong direction.

So let’s start with the basics.

Silicon (pronounced si-li-kən or si-lə-kän) is an element, a chemical substance that consists of just one type of atom, in this case, number 14 on the periodic table. Although Antoine Lavoisier and Humphry Davy both worked with it, Swedish chemist Jons Jacob Berzelius is often identified as its discoverer in 1823. It is, by weight, the second most common element in the earth’s crust. Pure silicon looks gray, and shiny when polished. It is used in computer chips, LCD displays, and solar cells.

The word silica (pronounced si-li-kə) comes from the Latin word for flint, which is “silex” (flint is a hard gray rock consisting mostly of silica – it was flaked or ground in ancient times to form tools). It’s also called silicon dioxide, or SiO₂ (spoken “ess-eye-oh-too”) and is a hard, colorless chemical compound. It occurs in nature as the mineral quartz, and is component of many common rocks like sandstone and granite.

Silica is the oxide of silicon. An oxide is a chemical compound containing at least 1 oxygen atom and 1 other element. SiO₂ contains two oxygen atoms for every silicon atom. When these two elements combine, they make a clear solid very different from either the shiny silicon or the oxygen gas.

Silica is the main ingredient in glass, and here at the Museum we love to make stuff out of glass. Here are a couple of glass animals made in the Flameworking booth. We’ve been developing goat and sheep prototypes recently because in the Chinese zodiac, 2015 is the year of the goat (or the year of the sheep or ram, depending on which source you ask).

So silica is what glass is made of, but there are different types of glass with varied characteristics, and those characteristics are often determined by varying the ingredients having differing chemical formulas. Glasses that start with silica but have other added ingredients are called silicates (pronounced si-lə-kāts or si-lə-kəts). The most common type of silicate glass is called soda lime glass. It contains mostly silica, with soda ash added to help it melt as well as limestone to stabilize it. Soda ash is also known as washing soda, and used to be made by burning plants that live in salty, desert soil, or seaweed and kelp. Limestone is the material in blackboard chalk, white marble landscaping stones, and some cements.

Soda lime glass is used to make windows, drinking glasses, bottles, jars and most other household glass. When you visit the Museum you’ll see our highly skilled glassblowers making beautiful glass objects (like the ones pictured below) from soda lime glass at the Hot Glass Show.

In the Museum’s Flameworking demonstrations, we use a glass called borosilicate.

Like soda lime, it includes silica and soda, but it adds one of the oxides of the element boron (as well as aluminum oxide). Boron is probably most familiar as borax, used as a household cleaner. Boron added to glass enables objects to withstand faster temperature changes than soda lime glass without breaking. So borosilicate is often used for scientific lab ware, coffee pots, and baking dishes. It’s also quite nice for sculpting. Since you can heat and cool it more unevenly than soda lime glass without causing it to break, it is particularly well-suited to making complex shapes and doing very careful detail work.

Now we’ve covered the basics of silica, silicate, and silicon, but what about silicone (pronounced si-lə-kōn)? How does that fit into the picture? Silicone is a plastic- or rubber-like polymer that includes silicon in its make-up. Typically heat-resistant, silicones are best known for their use in caulks, glues, lubricants and cooking utensils. The first commercially useful silicone was invented in Corning by chemist Frank Hyde when he was studying new ways of making silica!

Glass is one of those things we interact with daily in many ways and usually don’t think twice about. But glass is diverse and versatile, so it’s interesting to take a closer look and begin unraveling some of the artistic, scientific and technical language associated with it. Next time we’ll consider glass and transparency. Why is glass transparent and why is it sometimes not? What does it mean to be translucent or opaque? The ability to transmit or reflect light is a characteristic that makes glass very appealing in art applications, so we’ll look at how and why artists choose to use it in so many different ways.

Read the first installment of The Innovation Center: Where Art and Science Happily Meet.