Grades 3–5 · Materials & Matter
How can grains of sand become a glass bottle?
A glass bottle can begin with silica-rich sand, mixed with other ingredients. For common soda-lime glass, soda ash helps the mixture become workable at a lower temperature than pure silica would need. Limestone supplies another ingredient that helps the finished glass resist attack by water. Recycled glass can also join the mixture.
In the diagramHot glass can be shaped; cool glass holds its shapeSoda-lime glass · a noncrystalline solid when coolHeated mixtureAnnealed objectSand + other ingredientsControlled slow coolingAnnealing reduces internal stress from uneven cooling.
Inside a very hot furnace, the ingredients form a glass melt. While hot, it can flow and be shaped. A mold can help give a bottle its outside shape, while air forms the hollow inside. As the glass cools, it becomes too stiff to flow and keeps the shape. Cool glass is a solid, but its atoms do not form the repeating long-range pattern found in a crystal.
Cooling must be controlled. If different parts cool and contract unevenly, stress can remain inside the object. Annealing gives the glass time to relax this stress during a carefully controlled cooling stage. The result is an everyday object whose shape and reliability depend on both the ingredients and the way it was made.
About this explanation
Starting knowledge: Recognize melting and cooling and that a mixture may behave differently from its ingredients.
Sources
- Corning — How Glass is Made
- Corning Museum of Glass — Annealing
- Corning Museum of Glass — Batch
- Corning Museum of Glass — Mold blowing
- Corning Museum of Glass — Glass