Borosilicate glass: overview and history
German glass chemist Otto Schott, working in Jena, Germany, is credited with pioneering borosilicate glass. In 1893, Schott developed a glass formula incorporating boron that dramatically reduced thermal expansion and improved resistance to chemical attack and heat shock. His company, Schott Glaswerke (founded with Ernst Abbe and Carl Zeiss), commercialized this as “Duran” glass, initially targeted at laboratory glassware.
India’s borosilicate story centres on Dr. Sridhar Raghunath (S.R.) Lele, a glass technologist who led the effort to indigenize borosilicate glass manufacturing in the country. On December 14, 1962, he incorporated a company in Mumbai called the Industrial and Engineering Apparatus Company Private Limited, in technical collaboration with America’s Corning Glass Works, which brought technology, blueprints and manufacturing expertise while taking roughly a 49 percent stake in the venture.
Borosilicate glass is made primarily from silica (SiO₂) and boron trioxide (B₂O₃), typically around 70–80% silica and 7–13% boric oxide, with smaller amounts of soda ash, alumina and potash. This composition gives it a very low coefficient of thermal expansion, about 3× lower than ordinary soda-lime glass, which is why it resists cracking under rapid or uneven temperature changes.
Types of borosilicate glass
- Type I / Low-boron borosilicate (Pyrex-type, ~13% B₂O₃): the classic heat-resistant glass used in lab glassware, kitchenware and bakeware.
- Type II / High-boron borosilicate: even higher chemical durability, used in pharmaceutical vials and specialty applications.
- Aluminosilicate-borosilicate variants: used in high-end lab equipment requiring extra durability.
- Fiberglass-grade borosilicate (E-glass, C-glass): used for insulation and reinforcement fibre.
- Vycor / high-silica borosilicate: 96% silica, extremely heat resistant, used in high-temperature applications.
- Tempered / toughened borosilicate: used for modern cookware and appliance windows, such as woodstove glass.
Glass composition with expansion
| Chemical | 3.3 Expansion | 4.9 Expansion | 5.4 Expansion |
|---|---|---|---|
| SiO₂ | 80.60% | 75.00% | 70.00% |
| B₂O₃ | 13.00% | 10.50% | 7.50% |
| Na₂O | 4.00% | 5.00% | 6.50% |
| Al₂O₃ | 2.30% | 7.00% | 6.00% |
| CaO | – | 1.50% | <1.0% |
| Fe₂O₃ | – | – | 1.00% |
| TiO₂ | – | – | 5.00% |
| K₂O | – | – | 1.00% |
| BaO | – | – | 2.00% |
| MnO₂ | – | – | – |
| MgO | – | – | – |
Thermal properties
| Property | 3.3 Expansion | 4.9 Expansion | 5.4 Expansion |
|---|---|---|---|
| Coefficient of thermal expansion (20–300°C) ×10⁻⁶ K⁻¹ | 3.3 | 4.9 | 5.4 |
| Annealing point °C | 565 | 565 | 560 |
| Softening point °C | 820 | 785 | 770 |
| Density at 25°C g/cm³ | 2.23 | 2.34 | 2.42 |
International standards
Globally, glass composition and quality are governed by a set of recognized international standards.
| Standard | 3.3 Expansion | 4.9 Expansion | 5.4 Expansion |
|---|---|---|---|
| ASTM E-438 | Type 1 Class A | Type 1 Class B | Type 1 Class B |
| US Pharmacopoeia (USP) | Type 1 | Type 1 | Type 1 |
| European Pharmacopoeia (EP) | Type 1 | Type 1 | Type 1 |
Vitrics laboratory glassware is manufactured from 3.3 borosilicate glass and adheres to these established benchmarks, ensuring consistent performance across thermal resistance, chemical durability and dimensional accuracy.