7.9 Technical Notes
Brewsters fringes are a visual effect seen as a rainbow visible within the unit. Brewsters
fringes are not a deterioration of the unit or glass but an effect created when light passes
through two panes of glass of the same thickness, the resulting light refraction becoming visible
a rainbow effect.
Brewsters fringes can be confirmed by pressing one surface of the unit. The rainbow effect will move and colours change as the one glass surface is depressed and released.
Brewsters fringes are normally avoided by using different thickness of glass for each pane of the IGU.
Newtons rings are a visual effect created when the centre area of the glass panes making up an IGU come into close proximity to each other or in fact touch each other. It will appear as a circular or semi circular rainbow effect in central areas of the unit. This could be the result of the incorrect airspace for the unit size, manufacturing faults, temperature related pressure changes or improper pressure equalisation or a combination of the above.
Multiple reflections can be present when viewing an
object’s reflected image in an IGU. The use of reflective glass as outside panes, and/or Low E glass as the inside pane, gives a greater reflection. Whilst it is not a common problem, a certain amount of double imaging is inherent in an IGU due to the glass deflecting under normal temperature and pressure changes.
The use of tinted, reflective or Low E coated glass in an
IGU can present increased thermal breakage risk compared to single glazing. Factors such as building orientation and design, framing, and internal blinds or screens will influence the thermal breakage risk. Toughening or heat strengthening of tinted or reflective glass can be offered as a solution in the absence of a detailed thermal breakage analysis.
Extra care should be taken with tinted laminated glass as it is hard to achieve a good clean cut edge condition. It is often advisable to edgework the glass edge.
The application of film products, paper, posters or paint will increase the possibility of thermal breakage.
UV light will degrade exposed edges of IGUs unless special GlassTech® Structural+ units are used. All perimeter edges must be glazed in or flashed to protect the edge from UV rays or the warranty will be void.
Units transported to and installed at altitudes greater than 1200m above sea level may exhibit altitude pressure problems and must have capillary tubes for pressure equalisation. Contact Metro GlassTech for details.
Setting block use and positioning are critical if both panes of the unit are to be uniformly supported and to maintain the unit sealant above any trapped water. Drainage is required in the centre and either side of the blocks.
Frame system supplier proprietary setting blocks should always be used. Metro GlassTech setting blocks can be supplied for flat sill rebates only. Setting block material must be a recognised material, such as Santoprene or EPDM and be 80-90 Shore A hardness.