Standard glass is made primarily of silica (sand), soda ash, and limestone. While naturally clear, glass can be transformed into a vibrant spectrum of colors through several fascinating chemical processes.
1. Transition Metal Oxides
The most common method involves adding metal oxides or salts to the glass while it is in a molten state. These metals absorb specific wavelengths of light, allowing only certain colors to pass through.
| Metal Oxide/Salts Added | Resulting Color |
|---|---|
| Iron Oxide | Green (common in beer bottles) or Yellow |
| Cobalt Oxide | Deep "Cobalt" Blue |
| Copper Oxide | Turquoise or Red |
| Manganese Dioxide | Purple/Amethyst |
| Gold Chloride | Ruby Red (vibrant and expensive) |
| Sodium Chromate or Ferrous Oxide | Green |
| Selenium Oxide Orange | red |
| Ferric Salt or Sodium Uranet Fluorescent | Yellow |
| Gold Chloride or Purple of Cassias | Ruby red |
| Cuprous Oxide, Cadmium Sulphide Glitter | red |
| Cupric salt | Peacock Blue |
| Potassium dichromate | Green and green yellow |
| Cuprous salt | Red |
| Cadmium sulphide | Yellow like lemon |
| Carbon Brownish | black |
2. Colloidal Particles
In this method, tiny particles of a substance are suspended throughout the glass. Rather than a chemical reaction, these particles cause light scattering. A famous example is "Selenium Ruby" glass, where selenium and cadmium particles create a brilliant red hue.
3. The Tyndall Effect (Structural Color)
Sometimes, glass isn't colored by pigments but by how light hits it. By cooling the glass at specific rates, microscopic crystals form within the structure. These crystals scatter shorter wavelengths of light, often resulting in milky whites or opalescent blues.
4. Photochromic Glass
Used primarily in "transition" eyeglasses, this glass contains silver halides. When exposed to UV light, the silver molecules undergo a chemical change that causes them to cluster and darken, effectively turning clear lenses into sunglasses in seconds.