An A-Z guide to glass (part 1)

In this two-part series, Phil Brown, European regulatory marketing manager at Pilkington UK, offers a guide to the trickier words and phrases in the glass and glazing vocabulary.
Do you know your ‘gaskets’ from your ‘hermetic seals’? The glass and glazing lexicon can be a tricky one to understand, with the language stemming from the deep corners of physics, manufacturing, technology and construction.

As such, phrases, words and metrics we use can often be confusing. For example, should we use IGU or DGU? And what’s the difference between float and annealed glass? We hope this serves as a helpful guide to the cohort of young talent entering the industry, and provides a useful refresher for those veterans too.

A – Annealed glass: Another term for ‘ordinary’ glass, most commonly used for float glass. Glass that, immediately after it has solidified into the required form and while still at a high temperature, is slowly cooled to minimise the internal stresses in the glass. Annealed glass, when broken, gives large fragments with sharp edges and so is not usually classifiable as a safety glass.

B – Brewster’s fringes: A rainbow-like effect visible under certain lighting conditions, in an insulating glass unit when the two panes of glass are almost exactly parallel to each other. This is an optical effect, and not a defect.

C – Coated glass:A glass substrate to which an inorganic coating has been applied, either a pyrolytic coating, usually applied on-line (ie, during the manufacture of the float glass) or a sputtered coating applied off-line (ie, in a separate facility post-manufacture).

D – Deflection: This is how much something moves out of true plane (or bends) when a load, like snow or wind is applied. Standards generally place restrictions on the amount by which glass can deflect, dependent upon the application.

E – Emissivity: The ability of a surface to absorb or emit heat radiation. Glass naturally has a high emissivity. However, when transformed into low emissivity (low-e) glass, the surface does not absorb the radiated heat, but reflects it back into the room, enhancing the U-value (explained under ‘U’) of the glazing.

F – Float glass: This simply defines glass that has been manufactured by floating molten glass on a bed of molten tin until it sets, producing a product with surfaces that are flat and parallel. Pilkington invented this process in the 1950s.

G – Gaskets: These are <span style=”font-weight: 400;”>solid, preformed glazing materials used to separate glass from other parts of the fixing or frame. In any design, it is essential that there is no glass-to-metal contact and gaskets can help to achieve this.

H – Hermetic seal: Not a type of marine mammal, the edge seal of an insulating glass unit (IGU) is a ‘hermetic seal’ designed to prevent gas from passing through. It minimises the rate at which water vapour can penetrate the cavity.

I – Insulating glass unit (or IGU): The confusion here can be how it’s sometimes referred to as a double-glazing unit (DGU). The IGU is a construction consisting of two or more panes of glass spaced apart with spacer bars to form a cavity between the panes. Argon gas is typically used in the cavity of an IGU as it has a lower thermal conductivity than air.

J – Jumbo: Jumbo refers to the largest size of glass a manufacturer supplies (for Pilkington, this is 6,000mm x 3,210mm). It’s usually delivered on a special glass-carrying vehicle called a floatliner.

K – K (Part K): This part of the building regulations in England covers protection from falling, collision and impact.  It also incorporates the former Part N (glazing – safety in relation to impact, opening and cleaning).

L – Laminated glass: This refers to glass produced by combining layers of glass with polyvinylbutyral (PVB) or cast-in-place resin (CIP) interlayers to form sandwiches of material with specific design properties. In the event of breakage, the interlayer tends to hold the glass together, making the product ideal for safety and security applications.

M-Z next month</b>
In next month’s issue of Glass Times, we’ll see if you know your ‘manifestations’ from your ‘quenches’ and ‘rebates’.