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Fused Quartz Glass

Sight glasses made of molten natural quartz

Special Properties

  • Short-term application temperature up to 1100 °C
  • Cheaper than optical quartz glasses
  • High thermal shock resistance
  • Excellent chemical resistance
  • Very low thermal expansion
  • Good UV transmission

Typical Applications

  • Temperature resistant sight glasses
  • Front windows for UV lamps
  • Sight glass for flame monitoring
  • Mechanical quartz components
  • Protective sight windows
  • Glass for UVC-disinfection applications
  • UV drying / curing sytems


Natural quartz glass with sight glass quality

Made of natural fused quartz glass, we produce sight glasses for high thermal load, front cover glasses for UV-lamps and similar less optically demanding components. Since for such applications an optical quality is of secondary concern and a high transmissivity below 200 nm usually is not required, natural fused quartz glass is a good material choice for the fabrication of such and similar parts.

Natural fused quartz glass is produced by the melting of natural quartz. It has no such high optical quality and purity as our synthetic optical grade fused silica glass. For this reason, it is much more cost-effective especially at large dimensions and an ideal solution whenever an application does not place high demands on the optical quality. The thermal characteristics and the chemical strength however are comparable to those of optical quartz glasses and the high UV transmission down to about 200 nm is an interesting property.

Our fused quartz glass is made transparent by a less sophisticated mechanical polishing process. As mentioned, it does not offer an optical grade quality in regards to index homogeneity, flatness, purity etc, but it is clear and has almost no distortions or inhomogeneities when directly looked through with the naked eye. The possible thickness tolerances and the parallelism of the polished material is relatively coarse, but this is usually not an important factor in most areas of application for which these sight glass grade materials are predestined.


To request a quote for natural fused quartz glass with sight glass quality, please click on the following button.


Price quote for fused quartz glass
with sight glass quality



Fused Quartz Sight-Glass Express Service 48h- Express Service icon

For some thicknesses of our fused quartz glasses, we offer our 48h Express Service for the fabrication and shipping within two working days. Below please find the available thicknesses within the express service. Please select the express service option in the inquiry form:

Fused quartz express service thicknesses:
3 mm ; 5 mm

Dimensions are max. 500 mm x 500 mm within express service.




Transmission curve of natural fused quartz glass

Show optical transmissivity of Fused Quartz Glass
(Sight glass quality)



  • T > 90 % at 260 nm (at 3 mm thickness)

Refractive Index

  • nd = 1,459

Mechanical Properties

  • Density: 2,20 g/cm3
  • Young's Modulus: ca. 7,2 x 1010
  • Poisson number: 0,17

Thermal Properties

  • Coefficient of thermal expansion:
    approx. 0,55 x 10-6/K (25 - 300 °C)
  • Max. operating temperature:
    • short term use: up to approx. 1100 °C
    • long term use: up to approx. 850 °C
  • Thermal conductivity: approx. 1,4 W/K m

Electrical Properties

  • Dielectric constant εr: 3,75 (1 MHz)
  • Loss factor: < 2 x 10-4 (20 °C ; 1 MHz)
  • Specific resistivity: 7,0 x 10Ω x cm (350 °C)
  • Insulation capacity 5 x 10-7 V/m


All given details and specifications are mean reference values and are not guaranteed. In addition, please consider the "Notes on technical specifications"