Reflective & Coated Glass

The ability to apply surface coatings to large areas of glass (typically 3m by 6m) was essentially driven by the increased construction of buildings with large-area glazing in their design, primarily in the late 1940s. These effectively created greenhouses, which required a large amount of air-conditioning (and hence running costs) to maintain a comfortable internal temperature. Once it was understood and recognized that special coatings could be applied to a float glass surface to make it reflective to short wave radiation from the sun and/or longwave radiation from heat inside or outside the building, the demand developed for coated glass types as an alternative to using coloured glass to reduce the transmittance of solar radiation (coloured glass was comparatively expensive).

Initially, large-scale application of thin coatings to glass, and the subsequent modifications to handling and processing requirements took some time (often decades) to fully develop. Modern glass coatings are more user friendly, and largely completed using two processes – the Sputter Coating process, also known as Magnetron Sputter Vacuum Deposition (MSVD), which is applied to pre-cut glass in a room-temperature vacuum chamber, or the Pyrolytic coating process, which applies the coating to Float Glass as it is being produced on the float line.  While the Pyrolytic process is a newer method for the application of glass coatings, continued development of the sputter coating process has meant that the vast majority of commercially available coated glass used is applied using the sputter process.

Pyrolytic Coatings are a metal oxide layer applied on line during the float manufacturing process. The coating is fused into the glass surface at high temperature making it extremely hard and durable. Since the coating is durable it can be glazed to the outside (surface 1) or inside (surface 2) of the building – surface 2 is still the recommended surface for long-term durability. It can be handled and cut like standard float glass and processed into heat strengthened, toughened, laminated, curved glass and Insulating Glass Units. These products are also known as an ‘on line’ or ‘hard coat’ reflective glass.

Sputter Coatings utilise a high technology process in which metal particles are deposited on the glass surface in a vacuum chamber. Almost any non-magnetic alloy can be sputtered, the more common being stainless steel, silver, and titanium. Performance characteristics and colour depend on the alloy and coating density, but in general, they have better solar control performance than pyrolytic coated glass.
Sputter coatings are often called soft coats as the coating is more susceptible to damage than pyrolytic reflective glass when single glazed. Special care is required in cutting, handling, glazing, and cleaning. They are also known as vacuum-coated off-line coatings. These coatings are applied to monolithic.

Advancements in Sputter Coating technology have created more resilient “post temperable” coated glasses, which means they can be tempered (toughened) after they have been coated.  As the coatings are designed to deflect heat they can be difficult to toughen, so with the advent of these new coatings, it has also required glass processors to continue to upgrade their toughening lines to accommodate the processing of these new generation coated glasses.

Designing with coated glass offers a great variety of performance and appearance options, and the building designer should consider several aspects when investigating reflective and coated glass for projects:

  • The aesthetics of reflective glass in relation to the coating reflectivity and orientation of the building. Reflective products can offer the designer a multitude of colour options to enhance or transform a building’s appearance.
  • The performance of the glass reduces heat gain and cooling costs. Reflective glasses offer superior heat gain performance over tinted glass but this is at the expense of reduced natural daylight levels in a building. In general, reflective glass offers lower UV and visible light transmittance than tinted glass.
  • The ability of the glass to reduce heat loss and heating costs. This can be improved by using Low E coatings or Insulating Glass Units, or both.
  • Most reflective glasses absorb and reflect a greater amount of heat than normal tinted float and therefore are more prone to thermal breakage. Toughening or heat strengthening will prevent thermal breakage.
  • Toughening and heat strengthening of reflective glass will create some roller wave or visual distortion, which can be more apparent on reflective and coated glass (compared to non-coated glass).
  • Tinted float glass with sputtered coatings is normally heat strengthened or toughened.
  • Spandrel panels are normally heat strengthened or toughened.
  • Edges of all annealed coated glass must be good quality clean cut with minimal defects when the glass is being glazed. Sometimes flat ground edges on all sides are specified. Under no circumstances should reflective glass be glazed with damaged edges.
  • Some Building Consent Authorities (councils) set limits on excessive glass reflectivity (typically around 20%). Most monolithic products should therefore be glazed with the reflective surface to the inside (or surface #2). This will only marginally decrease performance but will enhance the colour of the glass and avoid the strong ‘mirror-like’ appearance when viewed from the outside. 
  • The protection of the coating from damage during construction or cleaning can be an important consideration – refer to the notes below regarding care of coated glass. Under no circumstances can abrasive cleaners be used on any coated surface.

Care of Coated Glass

Even though coated glass technology has advanced and modern glass coatings are generally far more durable than earlier options, they do still require specific care and handling to minimise the risk of damage and maximize the performance of the coated glass.

When handling coated glass, always use clean, oil-free vacuum pads or gloves.

Coated Glass Delivery and Storage:

  • Make sure the coated glass is always supported.
  • Protect the coated glass from knocks, abrasions, and excessive pressure – especially on edges.
  • Keep coated glass surfaces dry, clean, and interleaved with paper or similar approved products.
  • Do not mark or label the coated surface.
  • Do not bend the coated glass.
  • Do not store coated glass in direct sunlight or damp unventilated places.

Glazing Coated Glass:

  • Take care not to damage the coating when fitting into the frame, or with glazing tools, sealant guns, etc, or by leaning materials against the coated surface.
  • Glaze with coated surface as specified to the INSIDE or OUTSIDE.
  • IMPORTANT NOTE – many coated glass types require “edge deletion” or removal of the glass coating in the area’s which will be used for bonding (eg spacer and edge-seal bonding in IGU units, structural bonding to frame/building, edge banding applications, etc).
  • Remove excess glazing lubricants immediately and check regularly for reappearance.
  • Clean off splashes from plaster, mortar, or concrete before they harden.
  • Do not glaze sheets with damaged edges.
  • Do not use glass with shelled or severely damaged edges.
  • Do not glaze with coating exposed to weather unless checked and confirmed that this is the correct design.
  • Do not glaze with putty, acid cure silicone, or other incompatible sealants.
  • Do not apply solar films to any coated surface.
  • Do not mark or label the coated surface.

Cleaning Coated Glass

  • Always clean coated glass panels as soon as possible after installation, especially if there is a risk of leaching, run-off or spattering from other materials.
  • Only use proprietary cleaners or well diluted mild detergent for routine cleaning. 
  • Never use abrasive cleaners on or near coated glass.

Coated Glass from Metro

Metro Performance Glass stocks a wide range (size and type) of coated glass to suit the most common applications in New Zealand. If you require something that is outside any of the groups listed below, please contact Metro Performance Glass and we will investigate placing a special order from our suppliers (lead-time and indent costs TBC for special orders).

* For information on stocked glass thickness or maximum sheet sizes, please visit the following link: Glass Sheet Sizes 


Coated Tinted Glass

Tinted reflective glass allows multiple options for light filtration and color neutrality, so it’s appearance can be coordinated with a building’s framing, including spandrels, metal panels and even stonework. Reflective glass lets optimal light into your space, but also reduces glare from the sun, which can reduce the need for blinds and other window coverings.

Metro Performance Glass stock the following sizes of “classic” tinted coated glass:

  • For information on stocked glass thickness or maximum sheet sizes, please visit the following link: Glass Sheet Sizes 
  • Other thicknesses & sizes available by special order – please contact Metro Performance Glass for availability.

*Classic Tinted Coated: performance values to ranges: VLR 10-34%, VLT 19-24%, SC 0.42-0.57, U 5.78-5.80

Metro Performance Glass stock the following sizes of “Supersilver” tinted coated glass:

  • For information on stocked glass thickness or maximum sheet sizes, please visit the following link: Glass Sheet Sizes 
  • Other thicknesses & sizes available by special order – please contact Metro Performance Glass for availability. 

*Supersilver Tinted Coated: performance values to ranges: VLR 10-34%, VLT 29-51%, SC 0.49-0.60, U 5.62-5.81

Reflective Low-E Glass

For more details, please refer to the separate section on Low E glass products, or contact your local Metro Performance Glass or Metro Direct office.

Mirrored Glass

The first mirrors used by humans were most likely reflections in pools of dark still water or water collected in a simple vessel /bowl. As human fascination with reflections grew, understanding developed of the requirements for making a good mirror - a surface with a very high degree of flatness (preferably but not necessarily with high reflectivity as well), and surface roughness less than the light wavelength. Examples of early mirrors (polished pieces of stone, such as obsidian) have been found around the modern-day Turkey region and dated back to 6000BC (polished stone mirrors have also been found in Mesopotamia from 4000BC, and Central & South America from 2000BC).

Production of more sophisticated mirrors made of copper, bronze, silver, gold, and even lead developed later, however, because of the weight of the material these mirrors were quite small (by modern standards) - early metal mirrors rarely measured more than 200mm in diameter. These early metal mirrors were often embellished/surrounded with ornamentation and were primarily used for decoration/ornamental purposes.

Contemporary mirrors did not come into being until the late Middle Ages, and even then their manufacture was difficult and expensive. One of the production problems was that the sand used for the glassmaking often contained too many impurities to produce real clarity. In addition, the shock caused by the heat of adding molten metal for backing more often than not broke the glass.

Modern mirrors are typically made by silvering - spraying a thin layer of silver or aluminium onto the back of a sheet of glass. Justus Von Leibig invented the process in 1835. His wet deposition process involved the application of a thin layer of metallic silver onto glass through the chemical reduction of silver nitrate. The development of this process enabled mirrors to be manufactured on a much larger scale, and for the first time in history, ordinary people could afford to buy a mirror.

Most mirrors today are made by heating aluminium in a vacuum, which then bonds to the cooler glass.

Mirrors are now used for all kinds of purposes, from LCD projection to lasers and car headlights, optical and scientific apparatus such as telescopes, lasers, cameras, periscopes, and industrial machinery.

* For information on stocked glass thickness or maximum sheet sizes, please visit the following link: Glass Sheet Sizes  

At this time Metro does not offer a toughened safety glass mirror product, and it is important to note that a toughened safety glass mirror will normally show distortion in reflected images due to the glass toughening process.

Please check with your local Metro Performance Glass or Metro Direct office for any special orders, product availability, and delivery lead times.

Safety Mirror

The term safety mirror is generally used to describe round convex mirrors typically used for viewing at tight corners/intersections where the range of straight-line vision is restricted.

In the context of this document, safety mirror is used to describe flat mirror glass products with a vinyl backing. Vinyl-backed safety mirrors offered increased protection (compared to a conventional annealed glass mirror) in the event of accidental breakage. Where an annealed glass mirror will typically separate into large sharp pieces, vinyl-backed safety mirror fragments should not fall out/down and will be less likely to be penetrated, reducing the likelihood of serious injury. Vinyl backing is available in two options – standard or woven. The woven vinyl backing offers increased strength and tear resistance compared to the standard flat sheet vinyl backing.

Vinyl-backed safety mirror complies with NZS 4223 and AS/NZS 2208 as a safety glass, and can be supplied cut to size, drilled, and edge-worked.

It is important to note that there are special requirements for installing vinyl-backed safety mirrors – detailed information is currently being developed – please contact your local Metro Performance Glass or Metro Direct branch for assistance.

* For information on stocked glass thickness or maximum sheet sizes, please visit the following link: Glass Sheet Sizes

Please check with your local Metro Performance Glass or Metro Direct office for any special orders, product availability, and delivery lead times.

One-way Vision Mirror

A one-way mirror is a special type of mirror that appears reflective on one side (like a normal mirror) while allowing vision through from the other side. This is achieved by applying the reflective silvering layer but not applying the opaque coating, allowing for very slight transparency through the silvering coating. The perception of one-way transmission is enhanced when the reflective side of the mirror is brightly lit and the other (viewing) side is comparatively dark. This allows viewing from the darkened side but not from the more brightly lit side.

The difference in lighting levels required to achieve the one-way vision effect can be reduced by altering the silvering layer and glass types used. Typically standard one-way mirror manufactured with clear glass requires a minimum lighting ratio of 17:1. Using a more targeted one-way mirror type, the minimum lighting ratio can be reduced to 8:1. It is important to note that when lighting is installed to maximise one-way mirror observation, the lighting source must not shine directly on the mirror, as this will reduce the effect intended.

While some one-way mirror products can be toughened, caution is recommended when specifying this requirement as the toughening process is likely to create some optical distortion in the finished mirror.

As with standard mirror types, one-way mirror is not recommended for exterior installation.