Although we hope you do not have any issues with your glass we would like to take the opportunity to outline what to expect from your glass and HBD’s criteria for visual defects in glass and their acceptability. The page below will cover the following; double glazed units consisting of toughened, laminate or standard glass. Including any coatings or tints on or within the glass. 

Potential Distortions

With all glazing supplied, a certain amount of visual distortion is acceptable in the manufacturing process. There is also an acceptable level of defects that can e evident but occur naturally in this process. 

We always class damaged glass as unacceptable, it may be installed temporarily as a necessity to keep your home weather proof. It will always be replaced when new glass has bee ordered and delivered.

Our objective at HBD is to supply and install glass as free as possible of defects caused in manufacture. However you should know what to expect from your glass and accept minor imperfection/manufacturing visual distortions provided they fall within the scope of the following definitions and acceptance criteria. 

There will however be distinction between large pane glass units and what would be considered ‘standard size glass’. A large pane glass unit would be any pane ober 2.5 sq meters or over. In the vase of large glass the end user/ client must be aware that the defect threshold will increase as the glass area percentage becomes higher.

Roller wave

Roller wave is a common type of visual glass distortion that may be visible in toughened glass. It is caused during the toughening process when heated and slightly molten glass is passed over large rollers while it is cooled. As s result the glass may have a slightly waved finish to the surface.

This does not affect the strength or durability of the toughened glass and is only visually detectable under certain circumstances. 

As a rule, the visual appearance of roller wave in glazing is not classed as a glass defect.

Stain Patterns

Brewsters Fringe can be seen as a rainbow within a glass unit. These stains are not a deterioration of the unit or the glass, but an effect created when light passes through two panes of glass which are parallell and of the same thickness. This can be confirmed by pressing one the surface of the unit, the rainbow effect will then move and colours may change as the surface is depressed and released. 

This visual phenomenon can also be known as stain pattern, quench marks, leopard spots or anisotropy is an accepted characteristic of the glass toughening process and is not classes as a glass defect. 

External condensation

Condensation may occur with glass units which have low U-values and significantly reduce heat loss from your home. Under localised climatic conditions this can lead to moisture condensing on to the outside surface of the unit.

This is not a fault but rather demonstrated that the product is thermally efficient. 


Other visual distortions in standard size units

If there are any other visual distortions in glazing they should be inspected to determine what they are and if they are classed as acceptable within the guidelines from GGF.

Upon inspection we will use the guidelines as detailed below whilst looking through the glass in natural light. The glass will be classed ‘acceptable’ if the following are neither obtrusive nor bunched together:

  •  Bubbles or blisters no longer than 25mm. Small holes partially or wholly enclosed by glass which normally contain air. These may be spherical or non spherical dependent on the mode or formation.
  • fine scratched, no longer than 25mm. A long narrow surface flaw produced by a hard object which produces a perceptible depression.
  •  Sleek, no longer than 25mm. A fine scratch with no perceptible depression. 



  • Scare, no longer than 25mm. A scratch which is visibly white. 
  • Minute particles, no longer than 1mm. Loose manufacturing detritus that may remain within the unit after manufacture.
  • Inclusions. Insoluble matter retained within or on the surface of the glass during manufacture.
  • Visual effects. Toughened and toughened/ laminated glass as used in HBD installations is a processed glass. It is acceptable that a small amount of distortion may be visible through such glass. Using sealed glass units increases the umber of reflections which may accentuate any visible visual distortion. In addition, metal oxide coatings such as Low-E coatings may produce momentary visual effects in the surface of glass. 

Inspection Criteria

The glass area to be viewed is the entire vision area with the exception of a 50mm wide band around the whole perimeter of each glass pane. Any defects falling within this area are acceptable. 

The units shall be viewed at near normal incidence, this means at right angles to the glass surface from inside the room, standing at a distance of no less then 2m away from the unit (for annealed glass) and 3m away for all other glass types. The assessment of visual quality of the panes of glass should be carried out in natural daylight but not in direct sunlight and with no visible moisture on the surface of the inner or outer glass panes. 

The use of strong lamps and/or magnifying devices is not allowed. It is not permitted to find defects at close range and then mark them so they are visible from the viewing distance. Obtrusiveness of faults shall be judged by looking through the glass – not at it. 

Get a Quote