Glass Properties

At Cambridge Glassblowing we specialise in the two main types of glassware, Borosilicate Glass and Fused Quartz (Silica). Below we have some relevant technical data that will explain their unique properties. The information given here is only a brief summary, further technical information is available on request:

Borosilicate Glass

Borosilicate glass is widely used for laboratory glassware, either mass produced or as custom made. Borosilicate glass has excellent thermal properties with its low coefficient of expansion and high softening point, it also offers a high level of resistance to attack from water, acids, salt solutions, organic solvents and halogens. Resistance to alkaline solutions is moderate and strong alkaline solutions cause rapid corrosion of the glass, as does Hydrofluoric acid and hot concentrated Phosphoric acid.

Chemical Composition
Physical Properties
SiO2 = 80.6% Coefficient of expansion (20°C–300°C) 3.3 x 10-6 K-1
B2O3 = 13.0% Density 2.23g/cm3
Na2O = 4.0% Refractive index (Sodium D line) 1.474
Al2O3 = 2.3% Dielectric constant (1MHz, 20°C) 4.6
Optical Information Specific heat (20°C) 750J/kg°C
Refractive index (Sodium D line) = 1.474 Thermal conductivity (20°C) 1.14W/m°C
Visible light transmission, 2mm thick glass = 92% Poisson’s Ratio (25°C – 400°C) 0.2
Visible light transmission, 5mm thick glass = 91% Young’s Modulus (25°C) 6400 kg/mm2


Pressure Data
Whilst it is possible to pressurise glassware, extreme care should be taken and we suggest you contact Cambridge Glassblowing if your application requires pressurising.

Critical Temperatures

  • 150°C – When working above this temperature care should be taken to heat and cool Borosilicate glass in a slow and uniform manner.
  • 500°C – The maximum temperature that Borosilicate glass should be subjected to and then only for short period of no longer than a few minutes.
  • 510°C – Temperature at which thermal stress can be introduced to Borosilicate glassware.
  • 565°C – Annealing temperature. When uniformly heated in controlled conditions, such as a kiln or oven thermal stress’s can be removed.
  • 820°C – Softening point at which Borosilicate may deform.
  • 1252°C – Working point, the temperature that glassblowers need to attain in order to work Borosilicate glass.

Fused Quartz (Silica)

Silica (SiO2) is one of the chief constituents of the earth’s crust. It is present in various forms, the most being quartz which is crystalline in character. Typical examples are siliceous sands and rock crystal. There are also various other crystalline forms such as tridymite and cristoblite. All types when fused at 2000°C give a vitreous material. Fused Silica Glass is a unique material with an unrivalled combination of purity, high temperature resistance, thermal shock resistance, good electrical insulation, optical transparency and chemical inertness. This material is widely used in the production processes of the semi-conductor industries.

The outstanding characteristic of silica glass is its very high degree of purity (99.99% SiO2).

It also has excellent thermal properties with an extremely low coefficient of expansion 0.55 x 106cm/cm°C (0-300°C). This makes the material particularly useful for optical flats 7 furnace windows, where its minimal sensitivity to thermal changes is of benefit. Another related property is its high resistance to thermal shock. Thin sections can be heated and cooled rapidly without cracking. Some technical references report, heating the material to 1100°C, then plunging into cold water with no adverse effects.

Thermal Properties
Mechanical Properties
Softening Point 1683°C Density 2.20 x 103Kg/m3
Annealing Point 1215°C Young’s Modulus 74 x 106KN/m2
Strain Point 1120°C Rigidity Modulus 32 x 106KN/m2
Continuous Operating Temp 1000°C Compressive Strength 20 x 106KN/m2
Electrical Information Tensile Strength 70 x 103KN/m2
Electrical Resistivity 2 x 1019 ohm cm at 20°C Shear Strength 70 x 103KN/m2
2 x 106 ohm cm at 800°C Moh’s Hardness 6
Dielectric Strength 10KV/mm at 20°C Optical
2.5KV/mm at 500°C Useful Optical Range Synthetic 180 –2000nm
Chemical Information Natural 275- 2000nm
Total Metallic Impurities 10ppm (Typical) Refractive Index nD(589 nm) – 1.458


Please contact us if you require more detailed information such as transmission curves or chemical impurity levels.