GANA Technical Publications

Mirrors: Handle with Extreme Care NEW!!
     The GANA Mirror Division has released a new version of this document.  This document is now available as a free download in Adobe PDF format.  To download this document (115 KB), please click here.

GANA Glazing Manual
     (The following is an excerpt from the GANA Glazing Manual relating specifically to mirror.)

     Virtually all mirrors for interior use are manufactured by the conveyor wet deposition method. Annealed or fully tempered glass is thoroughly cleaned by the application of cleaners and passing contact with oscillating scrub brush units. After the glass is cleaned and rinsed the surface of the glass is sensitized with a diluted solution of tin chloride. This surface treatment allows for the deposition of silver. Silver nitrate is sprayed onto the sensitized surface of the glass along with other chemical configurations. The final outcome is the formation of a uniform silver layer on the glass.

     Once the silver layer is formed on the glass methods to protect the silver layer from oxidation are employed. A layer of copper is then deposited directly onto the silver. Copper can be applied in two ways either chemically or galvanically.

     Once the metal layers are attached to the glass they are covered by protective mirror backing paint. The mirror backing paint protects the metal layers from corrosion and from mechanical scratching. The paint can be applied either by passing the glass through a curtain of paint or by passing glass in contact with a roller paint coater. There are many mirror backing paint products available from a number of suppliers. They offer paint systems that are applied as a single coat or double coat. Both coating systems are effective and in the final measure apply an equal amount of paint to the metal surface. 

     Quality requirements for silvered annealed monolithic clear and tinted flat glass mirrors are provided in the American Society for Testing and Materials (ASTM) document C 1503 - Standard Specification for Silvered Flat Glass Mirror.

     Mirror manufacturers employ various techniques for adding value to their mirrors. The most notable are the application of a final clear coat to the painted surface for extra scratch resistance on the back and the chemical treatment of the glass viewing surface for increased scratch resistance and durability of the viewing surface.

     Tempered mirrors are manufactured using fully tempered glass as the substrate. There are optical characteristics inherent in tempered mirrors including roll distortion and the lack of a quality surface for silvering.

     Laminated Mirrors are manufactured by combining clear glass either annealed, heat-strengthened or fully tempered, and mirrored glass. 

     Safety Backed Mirrors are known as Organically Coated Mirrors in the CPSC 16 CFR 1201 and ANSI Z97.1 safety glazing standards. They are manufactured by applying a sheet of adhesive backed polyethylene material to the back of annealed mirrors. The backing material does not prevent breakage of mirrors but lessens the potential of injury on impact by retaining the fragments.

     Non-Silvered Mirrors consist of two types: pyrolytic mirrors and transparent/two-way mirrors.

     Pyrolytic mirrors are highly reflective coated glass products with performance characteristics approaching those of silvered mirrors. This product is promoted for use in shower doors and other areas where moisture can affect the substrate of silvered mirrors. 

     Transparent/Two-way mirrors are composed of reflective glass products and as such are not silver mirrors. Transparent mirrors are manufactured by both the pyrolytic deposition and vacuum deposition coating processes. Heavy density coatings are offered on clear and gray tinted glass. Transparent or two-way mirrors are designed to permit seeing through one side while giving the appearance of a standard mirror from the opposite side. Their major application is to permit undetected observation for study or surveillance in interior conditions such as learning centers in schools and universities, medical and psychiatric clinics, and security stations in casinos or high-traffic retail stores.

     The transparent mirrors work by reducing the visible light transmittance through the glass. To ensure proper performance the room lighting design and surrounding conditions must be carefully planned and executed. The glass surface in the subject room must appear to be a standard mirror. In order to achieve this condition the coated surface should be toward the subject room and the lighting ratios tightly controlled. For applications utilizing clear glass manufacturers recommend a lighting ratio of 10:1 subject's side to observer's side. If the lighting ratio drops to approximately 5:1 the subject may detect movement or silhouettes through the mirror. If 10:1 lighting ratios cannot be maintained a gray transparent mirror should be specified. Lighting ratios of 5:1 can be successfully used for gray transparent mirror products.

     Design considerations call for bright contrasting colors in the subject room and dark non-contrasting colors in the observer room. Light color surfaces or objects may be noticeable to the subject. The design of the observation room should also prevent sudden light ratio changes. Special care must be taken if transparent mirrors are used on more than one wall.

     Portions of the above information are from the GANA "Glazing Manual" - the most frequently referenced resource in the architectural glass and glazing industry. The "Glazing Manual" is an excellent additional to any technical library. Visit the TECHNICAL - MANUALS section of the GANA website to order your copy.

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