Glass is made from three simple ingredients: sand, soda ash, and limestone. If sand is heated to its melting point, its properties change and create glass. By adding soda ash, the melting point is slightly lower, which makes the process more cost-efficient. Finally, limestone is added to make the material more stable—without the addition of limestone, the glass material would dissolve in water. Glass is a particularly interesting material because it is difficult to classify as a solid, liquid, or gas. Molecularly, it is closer to a liquid but appears solid. For this reason, it is sometimes called a frozen liquid.   

PPG introduced a new method of making glass sheets in the 1920s called the Pennvernon technique, which used massive tanks that continuously melted the glass ingredients. A roller system within the tank would rotate the glass vertically until it was pushed to the top of the 30-foot mechanism. When it reached the top, it was cool and ready to cut. After several decades, a more efficient technique called the “float” method was introduced. This method involved floating molten glass onto the surface of a tank of molten tin. Because glass is lighter than tin it rises to the top in an evenly thick sheet.

The “River of Glass” now at the park pays homage to PPG and its history as a glassmaking factory. Cascading down the terraces, the river is made of large chunks of blue glass called cullets. Cullets are the leftover fragments of glass that are discarded in the glassmaking process due to imperfections or blemishes. Historically, young boys were responsible for cleaning the cullets from the machinery--a particularly gruelling and dangerous job. The design of the River of Glass can also be read as a reference to glass’s hard-to-characterize form, with the river representing the liquidity of both the glassmaking process and the finished product. Charles Jencks, a famed landscape architect, inspired the design for the river.

Detail shot of the River of Glass at Ariel-Foundation Park. The river is made from cullets, which are leftover or discarded byproducts of the glassmaking process. Image courtesy of Ariel-Foundation Park.

Video showcasing the more efficient “float” method used in the glassmaking process.

https://www.youtube.com/watch?v=tXvyRZY05CU

 

Sources

Keirns, Aaron J. Ariel-Foundation Park. Mt. Vernon, OH: Foundation Park Conservancy, 2015.

“PPG reinvented sheet-glass production.” Bill Amick  “Stories of Glass: Mount Vernon and Utica.” Looking Glass 2014 (Mount Vernon News, Feb. 18, 2014)