Coloured Glass
Coloured glass is glass that has a characteristic colour because small amounts of certain metal oxides, metallic compounds, or other colouring agents are incorporated into the glass during its manufacture. These substances selectively absorb certain wavelengths of visible light and allow other wavelengths to pass through.
Principle
The colour of glass is produced mainly by the selective absorption of light by the colouring ions or compounds present in the glass. Transition-metal ions are particularly important because their electronic transitions can absorb specific regions of visible light.
Common Colouring Agents
| Colour Produced | Typical Colouring Agent |
|---|---|
| Green | Chromium compounds or iron compounds |
| Blue | Cobalt compounds |
| Yellow | Cadmium compounds or certain iron compounds |
| Red | Selenium compounds or copper compounds |
| Violet | Manganese compounds |
| Amber/Brown | Iron and sulphur-containing colouring systems |
Uses of Coloured Glass
- Manufacture of decorative and ornamental glass.
- Production of coloured bottles and containers.
- Optical and laboratory applications where selective light transmission is required.
- Architectural and stained-glass applications.
- Containers in which protection from particular wavelengths of light is desirable.
Photosensitive Glass
Photosensitive glass is a special type of glass that undergoes a permanent structural or colour change when exposed to suitable ultraviolet (UV) radiation followed by controlled heat treatment.
Composition
Photosensitive glasses generally contain small amounts of photosensitive and nucleating components. Silver compounds are commonly used as the photosensitive component, while suitable halides and other additives can participate in the photochemical and subsequent heat-treatment processes.
Working Principle
- The glass is exposed to suitable UV radiation through a mask or selected pattern.
- Light-sensitive species in the exposed regions undergo photochemical changes.
- Controlled heat treatment promotes the formation and growth of microscopic crystalline or metallic phases in the exposed regions.
- The treated regions acquire different optical or chemical properties from the unexposed glass.
In this way, a pattern can be permanently produced within the glass. Depending on the composition and processing conditions, photosensitive glass can be made to develop contrasting opaque, translucent, or coloured regions.
Uses of Photosensitive Glass
- Manufacture of decorative glass articles.
- Production of precision glass components.
- Microstructuring and fabrication of small glass features.
- Optical and technical applications.
- Production of permanent patterns and images in glass.
Difference Between Coloured Glass and Photosensitive Glass
| Feature | Coloured Glass | Photosensitive Glass |
|---|---|---|
| Basic principle | Selective absorption of visible light by colouring agents | Photochemical change followed by controlled heat treatment |
| Special components | Metal oxides or other colouring agents | Photosensitive species and nucleating components |
| Effect of light | Colour is normally present as manufactured | Suitable light exposure initiates the photosensitive process |
| Pattern formation | Not an inherent feature | Patterns can be produced by selective exposure |
| Main applications | Decorative, architectural, optical and container glass | Technical, optical, decorative and microstructural applications |
Barasat Government College (West Bengal State University)