Technical advice | Inspecting glass and glazing

Since 2000 IDSystems has installed the highest quality Insulated Glass Units (IGUs) for our products. We work closely with a carefully chosen set of glass manufacturers to offer the highest standards of quality, whatever products from our range you choose for your home.

The nature of the way that glass is manufactured means that no processed glass used in doors and windows can be guaranteed to be 100% perfect, which is why we use the follow the Glass and Glazing Federation (GGF) guidelines to ensure the glass we supply meets and exceeds the established industry standards.

The Glass and Glazing Federation

Founded in 1977 the GGF is the largest glazing Trade Federation, recognised for their in-house technical expertise and covering all aspects of the glazing industry – from the manufacture of glass all the way through to the installation of completed windows and doors.

The GGF produce a technical datasheet that covers the visual quality of IGUs in detail, including acceptable imperfections such as:

– bubbles or blisters
– fine scratches not more than 25mm long
– minute particles, including small amounts of black sealant
– blemishes

Inspecting the glass in your doors and windows

It absolutely crucial that you carry out your own inspection of the glass when the glazing is installed and before further building works on your home are carried out. The delicate nature of glass means that dust and particles from site tools, rendering, plastering and even landscaping can potentially cause damage to the glass. It is also common for other tradespeople on site to work with close proximity to the glass once our doors and windows have been delivered or installed.

For your peace of mind every glass unit we supply is thoroughly checked at four stages of the process:

– during manufacturing before the sealed unit is put together
– once the sealed units have been made before it leaves the manufacture
– full quality assurance check by our experience team when it arrives at our factory
– a final check upon delivery or installation by our fitters or delivery staff

GGF guidelines

To assist our customers, the following helpful information will guide you on the correct method to inspect your own glass following the guidelines set out by the Glass and Glazing Federation.

How do I inspect my glass?

Stand inside of the room no less than 3 meters away from the glass and look through not directly at the glass, your focus should be on the space the other side of the glass not the glass itself.  Imagine it being how you would drive your car or wear your glasses, you don’t look at the windscreen or lenses but to the view behind.

“It is really important to understand that the primary function of glass is for looking through, not looking at”

– Inspection should only take place with natural daylight but not directly towards the sun
– No internal or external condensation should be on the surface of the glass
– Stand 3m away at right angles. Where it is not possible to standard 3m away stand as far away as you can
– Stand square on to the glass looking through the glass at 90 degrees
– Look through the entirety of the glass, but exclude a 50mm wide band around the perimeter

What is considered acceptable?

The glass is considered to be acceptable and would have passed quality checks if the following are not obvious nor bunched together.

– Bubbles, seeds, hairlines, blobs or blisters within the glass
– Fine scratches not more than 25mm long
– Small particles
– Blemishes

The obtrusiveness of blemishes is judged by looking through the glass, not at it, under natural light. It must be understood that the glass used in double or triple glazing is a processed glass, and so as a consequence, blemishes are to be expected.  The quality of IGU’s cannot be compared to glass used in other industries such as the automotive or optical glass industry.

What is considered unacceptable?

Sealed units with optical defects such as smears, finger prints or other dirt on the cavity faces of the glass, or extraneous material in the cavity are unacceptable, except in some cases where small particles of desiccant can be seen.  Desiccant is the absorbent material used in the spacer bar that runs around the perimeter of the IGUs.

How do different glass types vary?

Toughened glass – the thermal thoughening and heat strengthening process required to manufacture toughened glass may accentuate imperfections or visual distortions in double glazing
Laminated glass – manufactured with a thin layer of polymer between two panes of glass, there is a small chance of an increased number of blemishes due to the glass being made up from several layers
Thermally efficient coatings – glass with a thermal efficient coating (known as low-e) on the internal face of the inside pane of glass has a thin, transparent coating, generally comprised of a thin layer of a low emissivity material, that reflects infrared energy helping to enhance the thermal performance of the IGU. In some lighting conditions the coating may look like a transparent film or produce a haze, ie a cloudy look to the surface. When light coloured objects such as net curtains are placed close to the glazing they may look slightly darker.

Optical effects

Multiple reflections – this occurs in certain light conditions. This is caused by multiple surface reflections in each of the pane of glass, either double or triple.
Brewster’s Fringes – the rainbow effect. Small transitory rainbow effects are sometimes produced by the glass refraction of light.

Build up of condensation

Due to the high level of insulation offered by modern glazing it is common for moisture to condensate on the external face of the glass which may impact your view through your door or window. To help customers understand more about condensation forming we have produced a blog on the subject that you may find helpful.