Material Category: Optical Glass

Optical Glass Overview

Optical glass is mainly produced in a continuous melting process. Optical glasses acquire their properties through their chemical composition, melting process, and finishing methods.

There are two common optical glasses: flint glass and crown glass. The difference between the two lies in their index of refraction; however, both are known for their Abbe numbers generally under 60.

The table below shows comparable materials from different manufacturers.

Optical Glass Cross Reference Chart

Available Materials

Based upon customer demand, Sydor Optics offers Optical Glass made from the following substrate materials. Of course, if you don’t see a material you need, please contact a Sales Engineer, who will gladly discuss additional options that may be available.

Optical Glass

Optical Glass Properties

Principle Uses of Optical Glass

Optical glass is perhaps the most common type of material used in optical applications. It can be used in a variety of applications including:

  • Precision lenses
  • Pressure sensors
  • Viewing windows
  • Instrument windows
  • Laser systems
  • Beam displacement

Chemical Properties

Optical glass can include additives such as boric oxide (that make borosilicate glasses) and sometimes zinc oxide, phosphorus pentoxide, fluorite, and barium oxide.

Optical glass is generally water resistant, typically preventing staining in a humidity of 80% at 50 °C, and optical glasses are usually resistant to alkalis and other environmental factors.

Mechanical Properties

The mechanical properties of optical glass make it an excellent choice for numerous optical applications. The density of optical glass varies from 2.39 g/cm³ to 6.19 g/cm³.

Thermal Properties

The thermal properties of optical glass determine how the glass reacts in varying temperatures. The average coefficient of thermal expansion is between 7.00 and 9.00 x 10–6 /°C, which is generally higher than materials such as fused silica.


The global refractive index homogeneity of optical glass is better than 40 x 10–6. Most machined optical glasses can be delivered in homogeneities:
ISO 10110 part 4 homogeneity class 2 or better with a maximum variation of refractive index according ISO 10110 part 4 of ± 5 ∙ 10–6 and a maximum variation of the refractive index according to ISO 12123 and SCHOTT optical glass catalog of 10 ∙ 10–6.

Optical Properties

The two most prominent optical properties for optical glass are the index of refraction and the Abbe number.

Index of Refraction

Light will travel through materials with a lower index of refraction quicker than materials with a high index of refraction because the higher refraction bends light more.

Flint glasses have a high index of refraction whereas crown glasses have a generally low index of refraction, so they are often used together in application because of their conflicting properties.

Abbe Number

The Abbe number quantifies the amount of dispersion in a given spectral range. For example, a low Abbe number gives higher color dispersion while a high Abbe number reduces color aberration.

Optical glass has Abbe numbers ranging from 24 to 64.

Request high-volume production custom optics.

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