Glass & Glazing Facts

Visual Distortions In Glass

There is a certain element of distortion that can affect the appearance of the glass during the ‘toughened glass’ manufacturing process.

Anisotropy also known as stain pattern, quench marks or leopard spot is not classed as a glass defect. This ripple appearance of the glass is seen when viewed from a certain angle or time of day.

The characteristic pattern is caused by differing layers of ‘stress or tension’ when light passes through certain areas of the glass. It is not a cause for concern and will not affect the quality and longevity of the glass.

Condensation On Your Glass

With recent insulation requirements for glazing efficiency, the internal pane of the glass can have condensation issues. This is due to the temperature variation between the external and internal environment.

Water droplets occur depending on how much moisture there is in the home. For example, the steam from a kettle, drying washing, cooking, plants, or shower will naturally be absorbed into the air. When this water vapor comes into contact with a colder surface the air will be chilled.

Double and triple glazing can help to reduce the amount of condensation on the windows. However, it cannot completely eradicate the issue. If the air temperature within the room is low (not heated) and not well ventilated the air reaches a point when it becomes too saturated. This cooler air meets the colder internal glass and vapor will turn back into moisture. When this happens water droplets will occur on the glass. For more information view the Glass & Glazing Federation website.

Roller Wave Appearance On Glass

It is not uncommon to see roller wave patterns on toughened panels of glass. This visual distortion is caused after the float glass has been manufactured and has passed on to be toughened.

When the cut glass is heated to 600 degrees C, within a toughened furnace, it is then cooled rapidly by air. It is this cooling process that strengthens and stresses the surface layer of the glass, contracting the layers beneath and forcing them to contract. During this cooling process, the glass passes over large rollers. It is this process that can create the roller wave effect on the glass.

The appearance of ‘Roller Wave’ is not classed as a glass defect. However, there are levels of acceptance and these are carefully considered when these occurrences arise.

Other Signs Of Visual Distortions

If you notice any other visual distortions in the glass then you should contact us in the first instance so we can assess and survey the glass. Close range inspection to find defects is not an acceptable method for any notable discrepancies found within the glass.

All Surveys are performed no less than 2 meters from the glass and no less than 3 meters for toughened, laminated or coated glass. If possible the survey should be carried out during a dry day ensuring there is no moisture on the glass.

During the site inspection, there are certain criteria that we will be used to benchmark any noted visual distortions against. These are in accordance with the GGF and are marked as acceptable guidelines.

Quality Of Vision

Flat transparent glass, including laminated or toughened (tempered) or coated glass, is acceptable if the following are neither obtrusive nor bunched:

• Bubbles or blisters
• Fine scratches not more than 25mm long
• Minute particles no longer than 1mm.

This inspection is surveyed through the glass during natural daylight. Smears within the cavity of the glass are not acceptable.

Double reflections can occur during certain lighting conditions. These are caused by the many layers of coating on double glazing. Not always notable on every panel of glass and can vary considerably.

As noted above different treatments in the manufacturing process for toughened glass can be accentuated and laminated glass may have a few more blemishes but they do not in any way, affect the physical performance of the glass.