OCTOBER ONLY: 35% OFF
APS IS OFFERING 35% OFF ALL ITEMS GET YOUR QUOTE NOW
APS IS OFFERING 35% OFF ALL ITEMS GET YOUR QUOTE NOW
When new glazing goes in — whether that’s a double glazed window, a glass door, or an insulated unit as part of a renovation — it’s natural to look closely at the finished result. And when you look closely at glass, you often find something. A faint distortion. A small bubble near the edge. A pattern that appears when light hits at a certain angle. A cloudy patch that wasn’t obvious until afternoon sun came through.
The question most homeowners then face is: is this a defect, or is this normal?
It’s a reasonable thing to wonder, and the answer isn’t always obvious. Glass manufacturing is a precise industrial process, but it is not a process that produces optically flawless material. Building glass is assessed against a quality standard — not a perfection standard — and there’s often a meaningful gap between what consumers expect and what that standard actually requires.
This guide explains how glass quality is properly assessed in Australia, what the relevant standards cover, how to inspect glazing correctly, and how to distinguish between a genuine defect and a normal characteristic of the material.
It’s also worth keeping in mind that how glass appears can vary depending on the window style and configuration it’s installed in. Larger openings or operable formats like double glazed casement windows may highlight certain reflections or distortions differently compared to fixed or horizontal formats such as double glazed sliding windows. Understanding this helps set realistic expectations when inspecting new glazing and distinguishing between normal characteristics and genuine defects.
It’s important to separate surface-level glass quality issues from problems with the sealed unit itself. Marks such as roller wave, slight distortion, or coating variation may be normal characteristics under the standard, but persistent fogging, trapped moisture, or cloudy glass inside a double glazed unit point to a different problem altogether — seal failure rather than a manufacturing blemish. If you’re trying to tell the difference, this guide on how to tell if your double glazing has failed explains the clearest signs to look for and what to do next.
Two standards are most relevant to glass quality assessment in Australia.
AS/NZS 4667:2000 covers quality requirements for cut-to-size and processed glass. This is the primary standard for assessing surface quality, visual imperfections, and acceptable tolerance levels in architectural glass. When a dispute arises about whether glazing meets quality expectations, this is typically the standard that applies.
AS/NZS 4666-2012 applies specifically to insulating glass units (IGUs) — the sealed double glazed assemblies used in double glazed windows. It covers unit construction, edge seal performance, and quality requirements specific to the IGU as an assembled product, including what constitutes acceptable and unacceptable internal conditions.
Together, these two standards provide the framework for assessing whether building glass meets the quality expectations appropriate for its intended use. Neither standard requires glass to be free of all visual variation — they define the limits within which variation is acceptable.
Environmental conditions can also influence how glass performs and ages over time, particularly in coastal areas where salt air and humidity are constant factors. If your home is near the ocean, it’s worth understanding how double glazing performs in coastal homes, as these conditions can affect both long-term durability and how certain visual characteristics appear.
This is where most disputes go wrong before they even start. Glass looks different under different conditions, and informal inspection — standing close to the glass, looking in direct afternoon sun, using a torch or phone light — will almost always reveal something that looks concerning. That doesn’t mean anything is wrong.
The conditions for a valid glass inspection are defined in the Australian standard, and they matter. Assessing glass outside these conditions leads to false impressions in both directions — making normal glass look defective, or making genuinely poor quality glass look acceptable.
Stand at least three metres away from the glass. This is the specified viewing distance. Close-up examination is not a valid basis for assessing whether glass meets quality criteria. Many surface marks and minor blemishes that appear obvious at arm’s length are not visible at three metres — and if they’re not visible at three metres, they generally don’t constitute a non-conformance under the standard.
Use natural daylight. Inspection should be carried out in natural daylight conditions.
Do not inspect in direct sunlight. This is a specific and important exclusion. Direct sunlight dramatically amplifies the visibility of surface marks, distortion, and optical effects that are entirely within tolerance. A scratch or haze that appears striking in afternoon sun may be invisible in diffuse daylight — and the standard applies to diffuse daylight conditions, not to direct solar illumination.
View the glass at approximately 90 degrees to the surface. You should be looking through the glass, not at it at a shallow angle. Oblique viewing angles exaggerate distortion and surface irregularities well beyond what is seen in normal use.
The glass should be clean and dry. Moisture, smears, or dust on the surface can create the appearance of defects that don’t exist in the glass itself.
No magnification. Inspection should be done with the naked eye only. Using a magnifier, loupe, or phone camera zoom introduces a level of scrutiny that goes well beyond the standard’s requirements and the conditions of normal use.
For insulating glass units, the edge zone — typically a 50mm band around the perimeter — is excluded from the central viewing area assessment. Minor marks and imperfections that fall within this zone are assessed differently from those in the central area, reflecting the fact that this zone is often partially covered by window frames in normal installation.
The central viewing area is the primary zone of concern for visual quality assessment.
Within the properly applied standard, the following are typically acceptable:
Small seeds and bubbles within tolerance. Seeds are tiny gas inclusions that can occur during the float glass manufacturing process. Bubbles may also result from laminating or processing. The standard specifies size and frequency limits. As a general guide, bubbles under approximately 1mm are typically acceptable throughout; a single bubble between 1mm and 5mm per defined area unit may be within tolerance; bubbles over 5mm are not acceptable. Location also matters — proximity to the central viewing zone is assessed more critically.
Minor surface blemishes not visible from three metres. If a mark, scratch, or surface irregularity cannot be seen from the correct inspection distance under valid lighting conditions, it does not constitute a non-conformance.
Edge zone variations. Given that edge zones are partially concealed in installation, minor imperfections in this area are assessed to a less stringent standard than the central viewing area.
Visual effects inherent to processed glass types. This is discussed in more detail below, but the short version is that toughened, laminated, coated, and insulated glass all have normal visual characteristics that are not defects.
Some conditions fall outside acceptable tolerance regardless of viewing conditions:
Scratches visible from three metres in valid daylight. A scratch that remains clearly visible at the proper viewing distance and under diffuse natural light — not direct sun — is a potential non-conformance.
Internal contamination in insulated glass units. This is treated seriously under the standard. Fingerprints, smears, dust, debris, or foreign material on the cavity-facing surfaces of the glass (the interior of the sealed unit) are not acceptable. These surfaces cannot be cleaned after the unit is assembled, and visible internal contamination indicates a quality failure in the manufacturing or assembly process.
Oversized bubbles or seeds outside the defined tolerance. Where bubble or seed size and frequency exceeds the standard’s specified limits in the central viewing area, this is a non-conformance.
Visually disturbing damage in key viewing zones. Deep scratches, chips, significant surface damage, or obvious mechanical damage to the glass surface that would be apparent in normal use are not compliant.
This section addresses the most common source of confusion: the visual characteristics that are inherent to certain types of processed glass and are not defects.
Toughened (tempered) glass is produced by heating glass to a high temperature and rapidly cooling it. During this process, the glass passes through a furnace on rollers, and the combination of heat and roller contact can introduce a slight, periodic wave pattern into the surface. This is known as roller wave.
Roller wave is most visible when looking at reflections in toughened glass — a straight line reflected in the glass may appear slightly undulating. It is an inherent characteristic of the toughening process, not a manufacturing defect. All toughened glass has some degree of roller wave, and the standard accommodates this. If you’ve noticed that your sliding glass door or toughened window panel looks slightly wavy in reflection, this is almost certainly the explanation.
Perhaps the most commonly misunderstood characteristic of toughened glass. Anisotropy refers to the way toughened glass interacts with polarised light. The toughening process creates internal stress patterns in the glass, and when viewed through polarised lenses — including polarised sunglasses — these stress patterns appear as irregular patches of colour, sometimes described as leopard spots or iridescent patches.
Anisotropy is not visible to the naked eye under normal viewing conditions. It appears specifically when polarised light is involved. If you’ve looked at a window through polarised sunglasses and seen patches of colour or light variation, that is anisotropy — a normal characteristic of toughened glass, not evidence of a defect.
Glass with low-emissivity (Low-E) or solar control coatings may display slight colour variation or a subtle reflective haze under certain lighting conditions. Thin-film coatings can create interference effects that produce colour shifts depending on the angle of light. This is a physical property of the coating, not a fault in application.
An insulated glass unit is a sealed system. Changes in atmospheric pressure, altitude, or temperature cause the gas inside the unit to expand or contract, which can result in slight bowing or deflection of the glass panes. This is most visible in large panes where even small pressure differentials produce perceptible curvature. The deflection is dynamic — it changes with conditions — and is a normal behaviour of sealed units, not a structural failure.
Double glazed windows can produce a double reflection — where a single object reflected in the window appears as two overlapping images. This is a natural optical result of having two glass surfaces separated by a gap. It is more pronounced at certain angles and in certain lighting conditions. It is not a defect.
Laminated glass sometimes displays iridescent colour patterns — similar in appearance to the colours seen in oil on water — particularly in reflected light. These are known as Brewster’s fringes and result from light interference between the glass panes and the interlayer. They are a normal optical characteristic of the laminated glass construction, not a quality problem.
“The glass looks wavy when I look at the reflection of the sky.” Almost certainly roller wave in toughened glass. Look at the specification — if the glass is toughened, this is expected and normal.
“I can only see the mark in direct afternoon sun.” This is a classic example of inspection outside valid conditions. Direct sunlight is explicitly excluded from quality assessment conditions because it reveals imperfections that are within acceptable tolerance for normal use. This doesn’t guarantee there’s no issue, but it does mean you should inspect again under diffuse daylight from three metres before drawing conclusions.
“My polarised sunglasses show rainbow patches in the glass.” Anisotropy in toughened glass. Not a defect.
“There are fingerprints inside the double glazed unit.” This is a legitimate concern. Internal contamination on cavity-facing surfaces is not acceptable. Document it and raise it with your supplier or installer.
“There’s a small bubble near the edge of the pane.” Assess where it sits. If it’s in the edge zone and small, it may be within tolerance. If it’s in the central viewing area and larger than approximately 5mm, it may be outside tolerance. Inspect from three metres in natural daylight.
“The glass looks slightly different colours from different angles.” If the glass has a Low-E or other coating, colour variation with viewing angle is a normal coating characteristic.
“The glass looks foggy inside the sealed unit.” This is a separate issue from manufacturing quality — it indicates seal failure in the IGU, which is a product performance failure. See the article on double glazing failure for more detail on this.
If you’ve inspected the glass under valid conditions and still have concerns, here’s a practical approach.
Clean the glass thoroughly first and allow it to dry completely. Repeat the inspection — sometimes what appears to be a surface fault is simply a smear or residue.
If the concern persists, document it properly. Photograph the issue from the correct distance in diffuse natural daylight. Note the location on the pane, the approximate size, and which zone it falls in. Good documentation strengthens your position considerably.
Contact your supplier or installer in writing, describing the issue clearly and attaching the photographs. Reference the relevant standard (AS/NZS 4667:2000 for surface quality, AS/NZS 4666-2012 for IGU internal conditions) and ask them to assess the glass against that standard.
If the response is unsatisfactory and you believe the glass genuinely doesn’t comply, the Australian Glass and Window Association (AGWA) can provide guidance, and consumer protection pathways exist through state-based fair trading bodies for disputes with suppliers or installers.
The core principle in glass quality assessment is straightforward: the standard defines what is acceptable, and inspection must be conducted under the conditions the standard specifies. A lot of the confusion in this area comes from inspecting glass in ways that weren’t intended — close up, in direct sun, through polarised lenses — and drawing conclusions based on what those conditions reveal.
Most visual effects in building glass, particularly in processed types like toughened and laminated glass, are inherent characteristics of the material. Internal contamination in a sealed IGU is a genuine non-conformance. Surface scratches visible from three metres in diffuse daylight are a genuine non-conformance. Everything else requires assessment against the actual criteria before a conclusion is warranted.
When in doubt, inspect correctly first. Most concerns resolve themselves under proper conditions. Those that don’t have a clear pathway to resolution.
The primary standard is AS/NZS 4667:2000, which covers quality requirements for cut-to-size and processed glass. For insulating glass units (double glazed sealed units), AS/NZS 4666-2012 also applies.
At least three metres. This is the viewing distance specified for quality assessment. Marks and blemishes that are not visible from this distance are generally within acceptable tolerance.
No. Direct sunlight is specifically excluded from valid inspection conditions because it exaggerates surface imperfections well beyond what is present under normal use conditions. Inspection should be conducted in diffuse natural daylight.
Small bubbles may be acceptable depending on their size, location, and frequency. As a general guide, bubbles under 1mm are typically acceptable throughout the pane. Larger bubbles are subject to frequency and location limits under the standard. Bubbles over 5mm in the central viewing area are generally not acceptable.
These are anisotropy — a normal optical characteristic of toughened glass caused by internal stress patterns created during the toughening process. They are most visible through polarised lenses. Anisotropy is not a defect.
The slight wave distortion — called roller wave — is an inherent result of the toughening process, during which glass passes over rollers in a furnace. It is most visible in reflections and is a normal characteristic of toughened glass, not a manufacturing fault.
No. Internal contamination on the cavity-facing surfaces of a sealed insulating glass unit — including fingerprints, smears, dust, or debris — is not acceptable under AS/NZS 4666-2012. These surfaces cannot be cleaned after the unit is sealed.
The edge zone is typically a 50mm band around the perimeter of an insulating glass unit. This zone is treated differently from the central viewing area during quality assessment, reflecting that it is partially concealed by window frames in normal installation. Minor imperfections in the edge zone are assessed to different criteria than those in the central area.
Not necessarily. Coated glass (such as Low-E glass) can display subtle colour shifts and haze depending on the angle of light — this is a normal characteristic of thin-film coatings. If the haze appears inside a sealed double glazed unit, however, it may indicate seal failure rather than a glass quality issue.
Inspect the glass properly under valid conditions first — clean, dry, diffuse natural daylight, three metres distance, 90-degree viewing angle. If a concern persists, document it with photographs taken under those conditions and raise it in writing with your supplier or installer, referencing the relevant Australian standard. If the matter isn’t resolved satisfactorily, AGWA and state-based fair trading bodies can provide further guidance.