An A-Z guide to glass (part 2)

In this second part of our series on the trickier words and phrases in the glass and glazing vocabulary, Phil Brown, European regulatory marketing manager at Pilkington UK, offers an M-Z guide to the industry.

What do we mean by ‘safety glass’ and ‘toughened glass’? Do you get a rebate from HMRC or find it in a window frame?
The technical terminology of the glass and glazing sector reflects our fusion of physics, manufacturing, technology and construction. It can be difficult to get your head around.
Last month, we highlighted that Brewster’s fringes is a rainbow-like effect between two panes, not a hairstyle, and how a hermetic seal covers the edge of an insulating glass unit (IGU), and isn’t an animal.
We hope this final M-Z guide makes the industry more transparent to newcomers and provides a window of opportunity for veterans to brush up on their vocabulary too.
M – Manifestation: When glass can present a risk to those unaware that it’s there (think large runs of uninterrupted glazing), permanent patterns, logos, or other markings may be applied so they don’t present a danger. This is a requirement of Building Regulations, for example, Part K in England, and Section 4 of the Technical Handbook in Scotland.
N – Noise control: The characteristic of a glass that describes its airborne sound insulation. Noise control is measured by the reduction or attenuation of sound at specific pitches or frequencies in decibels (dB), or by sound reduction indexes, such as the weighted sound reduction index (Rw).
O – Off-line/on-line coating: Coating is the process of applying substances to glass to give it enhanced properties, like thermal insulation and solar control. Off-line coatings are applied after the glass has been manufactured. At Pilkington, this operation is undertaken using a state-of-the-art magnetron sputter coater. On-line coatings are applied while the glass is hot as part of the float glass manufacturing process.
P – Patterned glass: Glass manufactured by passing between two rollers, one of which forms an impression or pattern into the glass (hence it used to be called rolled glass). Our range of patterned glass is known as Pilkington Texture Glass.
Q – Quench: The part of the toughening process (see toughened glass) where glass is cooled rapidly, usually by blowing high pressure cold air at the hot glass. This is done to set up surface stresses in the glass.
R – Rebate: The part of the frame that holds the glass.
S – Safety glass: Glass conforming to BS EN 12600, which classifies the product as giving either no break or safe breakage when the glass is tested by dropping a swinging impactor from different heights, Class 3 (190mm), 2 (450mm) and 1 (1,200mm).
T – Toughened glass: Glass that has been heated past its softening point and chilled rapidly to build in a ‘surface compressive stress’, giving it greater strength and making it break into small fragments if broken. Pilkington’s toughened glass is up to five times stronger than ordinary glass of the same thickness, helping architects and builders find greater scope in their use of glass in buildings.
U – U-value: The U-value is a measure of the rate of heat transfer through any material, not just glass. Other building elements like roofs and floors, for example, each have their own U-value depending upon their construction. To put it simply, less heat passes through something with a low U-value than a material with a high one.
V – Vertical glazing: Glazing that is true vertical or within 15º of true vertical.
W – Window Energy Ratings (WERs): This tells you how energy-efficient your windows are. The rating system is based on a scale of G to A++, with A++ windows being the most energy-efficient. The system is similar to those introduced for household appliances, white goods and light bulbs.
X – X-ray glass: Glass of high lead composition intended to reduce penetration of X-ray radiation, typically used in hospitals and science laboratories.
Y – Young’s modulus (E): This is a measure of elasticity of a material, equal to the ratio of the stress acting on the materials to the strain produced. A typical value of E for soda-lime-silicate glass is 70GPa.
Z – Zebra board: This is a board with alternating black and white diagonal lines used to observe optical transmission and reflection qualities in glass.
This concludes our A-Z journey of glass and glazing vocabulary from annealed glass all the way to zebra board.