This specification defines the level of acceptance for visible defects in clear, tinted and coated glass in sealed double glazing units.
All glasses supplied should be free from defects caused in manufacture, handling, storage and transit. However, the buyer shall accept glass with minor imperfections provided that they fall within the scope of the following definitions and acceptance criteria.
Since the inspection of a glass unit will be based on visual examination, the terms used in stating acceptance criteria are defined as follows:
- Viewing Distance: The distance from the observer’s eye to the glass surface.
- Critical Area: An elliptical area, shown in the diagram, which lies centrally in the glass and whose major axis is half the longer dimension of the glass: the minor axis being one third of the small dimension of the glass.
- Edge Zone: A zone parallel to the edge of the glass, which extends round the perimeter of the glass, and is normally within the glazing frame or area.
- Viewing Area: The area of glass lying between the critical area and the Edge zone.
- Scratch: A long narrow surface flaw produced by a hard object, e.g. grit, which produces a perceptible depression.
- Sleek: A fine scratch with no perceptible depression.
- Bubble: 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: Insoluble matter retained within or on the surface of the glass during manufacture.
- Scar: A scratch which is obtrusively visible being normally white in colour.
Method of Visual Inspection
The double glazed sealed unit is to be mounted vertically so that the whole surface can be seen. The double glazed sealed unit must be examined from the room side. The double glazed unit should be examined in natural daylight and not in direct sunlight with no visible moisture on the surface.
- Viewing distance: A minimum viewing distance of 2 metres is to be used.
- Viewing position: A viewing position at right angles to the unit from room side.
- Viewing aides: No visual aids other than spectacles for normal visual correction shall be used.
- Visual focus: Vision to be directed at a point not less than 2 metres on the opposite side of the glass from the observer. This is to ensure that the glass is looked through and that the vision is not concentrated on the surface.
Minor defects / imperfections are to be accepted if they fall into the categories below:
- Defects within Critical Area
Scratches and sleeks which are not visible when examined as specified in Method of Visual Inspection are to be accepted. Bubbles and inclusions not greater than 1.5mm in maximum dimension are acceptable provided any such defects are at least 150mm apart. White scars are not acceptable.
- Defects within Viewing Area
Scratches and sleeks which are not visible when examined as specified in Method of Visual Inspection are to be accepted. Bubbles and inclusions not greater than 2.0mm in maximum dimension are acceptable provided any such defects are at least 150mm apart. White scars are not acceptable.
- Defects in Edge Zone
Scratches, sleeks, bubbles, inclusions, and scars are acceptable.
No matter how clean a pane of glass may appear, there may always be contaminates present on the surface. These are normally invisible to the naked eye. However, when condensation forms on the glass surface these contaminates can become apparent by influencing the rate of formation and appearance of the moisture. This variation in appearance may be random or present itself in distinctive patterns. Fingerprints are the most common contaminate but any contaminate which creates a hydrophobic layer will produce these effects. Window cleaning chemicals or degreasing agents are normally enough to remove these thin layers of material but some contaminates can be more difficult to remove and require mild abrasives for complete cleanliness. For example, deposits from glass carrying suckers can form chemical bonds to the glass surface. Therefore the patterns formed by condensation on glass surfaces do not indicate any fault and have no effect on the performance of the glass, mechanically or physically. It is an indication that the glass surface has been modified.
Flemish Glass Pattern
Due to the design of Flemish patterned stock supplied to us from the glass manufacturers, buff marks may occur on the pattern high points; this is unavoidable when annealed glass is transformed into toughened safety products, Village Glass cannot accept any complaints or liability for the visual quality caused in this process. Annealed Flemish is unaffected. We would urge that an alternative pattern be offered to avoid the visual quality of toughened Flemish.
Defects – Other
Optical phenomenon such as Rollerwave distortion, double reflections, and Brewsters Fringe are acceptable.