How to Understand Sliding Door Glass Quality Standards
How we check for glass quality in our sliding doors
Our team completes a professional assessment of the quality of glass used in every panel of your sliding or bifold doors. It’s part of our ODC quality assurance and an important final check. As an accredited contractor, we adhere to the highest technical standards in the glazing industry. We order, check and fit all the glass panes for the aluminium sliding and bifold doors we manufacture and this allows us to evaluate glass quality at all stages of the process. We have a highly experienced and technical team of surveyors who ensure our glass is fit for purpose.
The glass inspection process for ODC sliding glass doors and bifold doors
An inspection of all glass panels takes place from inside standing about 3 metres back from the glass – in daylight, but not in direct sunlight and from a 90 degree angle. The whole glass panel is inspected with the exception of a 50mm wide band round the edge.
Glass is considered to have acceptable quality of vision if the following are not obvious nor clustered together: totally enclosed seeds, blisters, hairlines or blobs, fine scratches not more than 25mm long and minute embedded particles.
The double-glazed sealed unit is mounted vertically so that the whole surface can be seen. It must be examined from the inside and in natural daylight/overcast sky and not in direct sunlight with no visible moisture on the surface.
Toughened, laminated or coated glass should be viewed from three metres, and no visual aids other than spectacles for normal visual correction should be used when checking glass quality.
GGF Acceptable Glass Quality Standards in Sliding Doors and Bifold Doors
The Glass and Glazing Federation’s Acceptable Glass Quality Standards defines the level of acceptance for visible distortions in clear, tinted and coated glass in sealed double glazing units. It’s important to know that a totally flawless piece of glass is extremely rare by the nature of its organic components and manufacturing process.
Terms used to describe glass quality explained
When glazing specialists talk about glass quality, these are some of the terms they use. Knowing them will help you understand how glass quality is defined within the industry.
Edge Zone: The edge zone is the zone parallel to the edge of the glass, which extends around the perimeter of the glass, and is normally within the glazing frame or area.
Viewing Area: The viewing area of a pane of glass is the area of the glass lying between the critical area and the edge zone.
Scratch: A scratch describes a long, narrow surface flaw on the pane of glass produced by a hard object, e.g. grit, which produces a perceptible depression.
Sleek: A sleek is a fine scratch on the surface of the glass with no perceptible depression.
Bubble: Bubbles in glass panes are small holes partially or wholly enclosed by glass, which normally contain air. These may be spherical or non-spherical depending on the mode of formation.
Inclusion: An inclusion in a pane of glass is caused by insoluble matter retained within or on the surface of the glass during manufacture.
Scar: A scar on a pane of glass is a scratch which is obtrusively visible and is normally white in colour.
What does it mean if the glass in sliding doors has acceptable minor imperfections?
All glass supplied should be as free as possible from defects caused in manufacture, handling, storage and transit. However, the customer will be asked to accept glass with minor imperfections provided they fall within the scope of the following definitions and acceptance criteria. Glass which falls within these quality standards is not considered to be faulty goods.
Quality glass ensures your focus is on the view and not the glazing
What defects are acceptable in glass fitted to sliding doors, bifolds and windows?
Minor defects/imperfections are to be accepted if they fall into the categories below:
Acceptable Defects seen within the Glass Viewing Area
Scratches and streaks which are not visible when examined as specified in Method of Visual Inspection are to be accepted. Bubbles and inclusions not greater than 2.5mm are acceptable provided such defects are at least 200mm apart. Seeds, blisters, hairlines or blobs are acceptable if they are no greater than 2.5mm. White scars are not acceptable.
Acceptable Defects seen within the Glass Edge Zone
Scratches, streaks, bubbles, inclusions and scars are acceptable.
Acceptable Condensation Patterning on Panes of Glass
Contaminants are often present on the surface of glass and are normally invisible to the naked eye. If condensation forms on the glass surface, then the contaminate becomes more apparent by influencing the rate of formation and appearance of the moisture. The variation in appearance may be random or present itself in distinctive patterns. Fingerprints are the most common contaminant which creates a hydrophobic layer that can produce these effects.
Window cleaning chemicals or degreasing agents are normally enough to remove most contaminants. The pattern formed by condensation on glass surfaces does not, therefore, indicate any fault, nor do they have any effect on the performance of the glass and are considered acceptable.
Acceptable Optical Phenomena in Panes of Glass
Distortions are an inherent characteristic of glass, and there are currently no Industry Standards relating to the acceptability of levels of distortions with the exception of bow, which is determined in EN12150.
Roller wave distortion occurs as glass passes over the rollers in horizontal, oscillating heat treatment furnace. As the glass heats up, it may sag between the rollers at the reversal of each oscillation, which then becomes set in place during the cooling process. This may produce roller wave distortion in the finished product. This type of distortion can create a reflection in heat-treated glass that can stretch and compress based on the observer’s movement in relation to the glass surface.
Brewster’s Fringes is a type of glass distortion that occurs when wavelengths of light meet when they are exactly 180 degrees out of phase. It’s a result of modern glass manufacturing methods. Edge Bow distortion occurs as a result of the heat treatment process and can be reduced through the correct control of the heating and cooling processes.
Nickel Sulphide Inclusion in Glass
Nickel Sulphide Inclusion (NIS) is a naturally occurring phenomenon in toughened glass. Glass can be heat-soaked, which reduces the risk of NIS, but this cannot guarantee to eliminate it completely. Glass breakage caused by Nickel Sulphide Inclusion is not covered by the ODC Glass guarantee.
Switchable privacy glass quality
Very small bubbles and/or visual distortion may be present on clear/non-switchable areas around notches/holes/cut-outs. Therefore provision must be made for coverage of 10mm around all notches/holes/cut-outs. Bubbles and distortion of this nature are acceptable.
An element of haze is present in all smart LCD switchable privacy glass products, even in its transparent state. The level of haze must be checked before ordering as haze will not be accepted as a defect.
(Version 1: Nov 2017)
Do the coatings on laminated glass and solar-control glass affect glass quality?
Multi-layered glass, for example, when two or more panels are laminated together, will increase the impression of visible distortions as the cumulative effect of each of the panels needs to be taken into consideration. Toughened, laminated or coated glass should be viewed from 3 metres. Coating on glass, in particular solar control coatings, increases the reflective property of the glass, and this can make visual distortions more noticeable, even though there is no distortion present.
How do you know your sliding doors have the best quality glass?
