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Tempered glass (ESG)

Tempered glass is a type of safety glass. It is widely used in construction, interior architecture, furniture-making, industrial production of machines (cars, household goods). Tempered glass is known as ESG (Ger. Einscheiben Sicherheitsglas).

Glass is tempered by heating it to a high temperature (620–680°C) and abruptly cooling it in a jet of compressed air, which produces compressive stresses in the surface layer, significantly increasing the strength of glass.

Tempered glass is more flexible and resilient to mechanical and thermal factors than annealed float glass, and is also safer, because it falls to small, blunt pieces after being broken (annealed glass pieces are dangerously sharp).

At Dubiel Vitrum, we use tempering to produce:

  • Tempered float glass (ESG)

  • Bent glass in cylindrical shapes (safety glass - ESG)

  • Heat strengthened glass (TVG, often called semi-tempered)

  • ESG float tempered glass painted with baked ceramic paint (flood-coating or screen printing with glaze paint)

The glass produced by Dubiel Vitrum bears the permanent CE mark, which confirms the product’s compliance with the PN-EN 12150 standard.


glass thickness

from 3.2 mm (4 mm recommended) to 19 mm

glass size

  • minimum: 300 x 50 mm (or minimum diagonal 300 mm)

  • maximum: 2,000 x 3,600 mm (recommended: 2,000 x 3,210 mm)

glass types

  • float

  • decolored

  • body tinted

  • etched (tempered with the smooth and etched sides towards the rollers)

  • painted with ceramic paint, single coat (tempered only with the smooth side towards the rollers)

  • coated (tempered with the non-coated side towards the rollers)

  • ornamented

glass processing limitations before tempering

  • glass must not have any sharp edges (edges and corners need to be at least blunted)

  • minimum internal cut-out radius is:

-  R=8 mm for 3-15 mm thick glass

-  R=10 mm for 19 mm thick glass

  • minimum diameter of holes in glass must be equal or greater than the glass thickness

  • distance between holes must be equal or greater than double the glass thickness (fig. 1)

  • distance from the hole edge to the glass edge must be at least double the glass thickness (fig. 1)

  • distance from the hole edge to a sharp corner must be at last six times the glass thickness (fig. 1)

  • distance from the hole edge to a rounded corner (at acute angle) must equal at least six times the glass thickness calculated from the hole edge to the theoretical sharp corner (fig. 1)

  • distance between drilled holes must equal double the glass thickness calculated from the edge of the drill (fig. 2)


if holes do not meet the tempering standards, the design may be altered by:

  • moving the holes

  • decreasing the diameter

  • joining the holes (making a kidney-shaped hole)

  • making a bridge


glass processing limitations after tempering

Once tempered, glass is not further tooled (e.g. it is not cut, drilled or its edges ground), as it entails a high risk of damaging the piece or weakening it permanently. However, tempered glass can be:

  • sanded

  • printed

  • painted with water based paint

APPLICATIONS of tempered glass:

  • monolithic glass (single, float and bent): partition walls, wall linings, doors, glassed-in structures, shower cabins, table tops, glass shelves, furniture glass

  • used in laminates: canopy roofs, balustrades and barriers, safety partitions, elevator panes, floors and ceilings, roofs

  • used in laminates and additionally processed: floors, anti-slip landings and stairs, UV printed or painted balustrades

  • decorative ice glass (permanent “finely-broken” glass effect): furniture-making and interior architecture


Anisotropy is a physical property of tempered glass (ESG) due to which splashes of color show in polarized light.

During tempering, different stress areas appear in its cross-section. These stresses result in rays of light being doubly refracted. If soda-lime-silica glass (ESG or TVG) is viewed in polarized light, stress fields are visible as gray or color areas, darker spots or stripes on the surface of glass panes. These places are called “polarization fields” or “leopard spots”.

Therefore, stress areas and anisotropic effects result from the glass tempering process. They can be seen at a particular angle and in certain installation configurations. The phenomenon disappears if the angle at which a given area of glass is seen changes.

According to the technical guidelines in force and the European standard EN 12150, anisotropy is regarded as a physical property of tempered glass and in no case can be treated as a defect.


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