Lecture 7 - Glass

Historical Context

  • Early architecture lacked glazed openings; windows were open or sealed with other materials, so the appearance of transparent barriers radically changed daylighting, comfort, hygiene and privacy.
  • Progressive milestones (only highlights explicitly stated in transcript):
    • 1950s – Sir Alastair Pilkington invents the Float-Glass process, industrialising perfectly flat sheet production.
    • Pre-float technologies (all produced small panes, hence traditional multi-pane sashes):
    – Sheet glass: mouth-blown into a long tube, tube split and reheated then flattened (ripple and distortion typical).
    – Crown glass: gather spun into a disc, panes cut from the disc; explains bull’s-eye centres and limited sizes.
    – Stained glass: cutting many small pieces, assembling with lead cames.
    – Cast glass: molten glass poured, rolled or pressed into a plate or patterned sheet—larger than blown but still size-limited.

Basic Composition & Physical Properties

  • Ancient recipe recorded by Pliny: 6060 parts sand : 180180 parts ash from marine plants : 55 parts chalk → yields a soda-lime glass.
  • Modern float/flat glass batch (typical):
    • ~70%70\% silica sand (SiO$2$) • 12–15%12–15\% soda (Na$2$O from soda ash)
    • 8–11%8–11\% lime (CaO)
    • Small proportions of alumina, magnesium oxide, etc.
    • Melt temperature ≈ 1500∘C1500^{\circ}\text{C}, then floated on molten tin to achieve uniform thickness & parallel faces.
  • Up to ~5050 additional chemical elements or compounds can be introduced to adjust:
    • Colour (e.g.
    – Fe, Se → greens
    – Co → blue
    – Ni/Cr → grey/bronze)
    • Viscosity & working range
    • Durability, UV response, electrical behaviour.

Principal Glass Categories & Their Significance

  • Clear Float (a.k.a. flat or annealed glass)
    • Baseline product straight off the float line; NOT strengthened.
    • Breakage → large, razor-sharp shards; therefore limited to low-risk areas unless further processed.
    • Variants:
    – Standard (green edge tint due to iron).
    – Extra-Clear ("low-iron") for show cases, furniture, shower screens; prized where true colour rendition needed.
  • Tinted Float
    • Metal oxides mixed in the melt; common colours: grey, bronze, green, blue.
    • Reduces solar heat gain & glare; yields aesthetic tone; still translucent.
  • Reflective (Solar-Control) Glass
    • Thin metallic coating deposited (pyrolytic or sputter).
    • Lowers visible-light transmission (VLT) & solar heat; façade designer must evaluate glare/reflection to traffic and neighbours.
    • Local case study: Wellington’s "Double XQX" tower.
  • Decorative / Obscure / Textured
    • Surface pattern rolled in or cast; privacy while admitting light.
    • Thickness range: very thin patterned sheet to 10–15 mm cast.
    • Brand example: Ozone Glass catalogue.
  • Wired Glass
    • Mesh embedded during rolling; historic fire-resistance role; now rare (pre-1980s) as other safety glasses supersede.
  • Sand-Blasted / Acid-Etched / Frosted
    • Surface abraded or chemically roughened; diffusion increases privacy but fingerprints show readily; used by glass artists (e.g. Basia, Wellington).
  • Colour-Backed (Back-Painted) Glass
    • Typically splashbacks; colour applied by spray or screen-print onto rear face then oven-cured.
  • Mirror Glass
    • Silver or aluminium coating with protective paints.
    • Two families: traditional (copper layer undercoat) vs. copper-free (better corrosion resistance).
  • One-Way Vision (Observation) Mirror
    • Half-silvered; requires lighting contrast (subject side brighter) to appear mirrored.
  • Laminated Glass
    • Multiple sheets bonded by interlayers (PVB, EVA, ionoplast, etc.).
    • Functions:
    – Safety: retains shards after impact.
    – UV filtration: blocks up to >99\% UV → protects furniture, artwork.
    – Acoustic damping; interlayer absorbs vibrational energy.
    • Specialty variants: liquid-crystal or electrochromic interlayer → glass turns opaque (milky) when powered.
  • Toughened / Tempered Glass
    • Annealed sheet reheated near softening point then air-quenched; surface compressive stress ≈100MPa\approx 100 \text{MPa}.
    • Fracture pattern: small cubic pellets → reduced injury risk.
    • Cannot be cut, drilled or edge-worked after tempering; all machining must precede the heat-treatment.
    • Usage examples: frameless balustrades, structural floors, phone screens, vehicle side windows.
  • Composite & Structural Flooring Systems
    • Multi-laminated tempered layers + interlayers; sometimes printed frit for slip resistance.
    • Example: Sky Tower (NZ) observation deck.
  • Screen-Printed / Ceramic-Fritted Cladding Glass
    • Inorganic frit fused onto glass during heat treatment; adds opacity, pattern, solar shading or signage.
  • Insulating Glass Units (IGU) – “Double Glazing”
    • Two (or more) panes factory-sealed around spacer; cavity filled with dry air or argon.
    • Benefits: reduced U-value (thermal), lower sound transmission, mitigates condensation; now mandatory in many jurisdictions.
  • Curved (Bent) Glass
    • Float glass reheated on molds or draped; curvature limits depend on thickness and furnace.
    • Must be bent before tempering/laminating; supplier example: GlassShape NZ.
    • Applications: shopfronts, shower enclosures, spiral balustrades.
  • Glass Blocks
    • Hollow or solid pressed units; used for translucent walls and occasionally floors (with steel grid support).
    • Provide diffusion, structural robustness, some fire separation.

Processing Terminology (Edgework & Machining)

  • Arriss: simple blunt arris to remove raw-edge sharpness.
  • Smooth Arriss: further sanding/polishing of arris.
  • Bevel: edge ground at a shallow angle; decorative light-band effect.
  • Flat Grind: edge ground flat but not polished (matte).
  • Flat Polish: grind + high gloss polish; optically clear edge used for shelves, tables.
  • Mitre: edge ground to 45∘45^{\circ} (or other) for corner joins; spec must nominate angle & polish level.
  • Holes & Cut-Outs
    • Drilled or CNC/water-jet shaped in annealed state ONLY; minimum edge distances & diameters governed by supplier tables.
    • Computer-Numerical-Control enables intricate profiles before tempering or laminating.

Mounting & Installation Systems

  • Traditional Exterior Glazing
    • Timber sash/frame: putty or glazing bead + sealant; allowance for wood movement.
    • Aluminium frames: extruded profiles with thermal breaks, drainage paths, pressure plates & gaskets.
  • Interior Glass Partitions
    • Floor & head channels (aluminium) or dry/wet-glazed pockets; enables demountable office fronts.
  • Structural (Point-Fixed) Glazing
    • Spider fittings, patch fittings, stand-offs anchor through drilled holes; common on facades, canopies, stair panels.
    • Examples shown: curtain wall, frameless revolving/roller doors, pivot doors with top/bottom steel plates.
  • Gabion-Glass Hybrid Façade
    • Stones + thick irregular glass chunks wired in cages; dramatic translucency and textural play.

Regulatory Framework (NZ-centric but conceptually universal)

  • Key documents: NZ Building Code, Acceptable Solution B1 (Structure), B2 (Durability), F2 (Hazardous building materials), and industry standard NZS 4223 (Glazing in Buildings)—parts 1-4.
  • Access: Victoria University Library databases; Ministry of Business, Innovation & Employment (MBIE) website downloads.
  • Historic but instructive: 1999 Human-Impact Flow-Chart (Blackboard resource) – decision tree for selecting safety, laminated or toughened glass.
  • Continuous updates mean designers must verify latest revisions before specification.

Practical & Design Considerations

  • Daylight vs. glare: tinted/reflective coatings trade visible light for solar control.
  • Safety hierarchy (worst to best):
    Annealed→Wired→Laminated→Tempered→Laminated + Tempered\text{Annealed} \rightarrow \text{Wired} \rightarrow \text{Laminated} \rightarrow \text{Tempered} \rightarrow \text{Laminated + Tempered}
  • Post-processing rule of thumb: any cutting, drilling, bending or screen-printing must precede tempering.
  • Fingerprint sensitivity: sand-blasted, acid-etched & high-gloss back-painted surfaces require cleaning strategy.
  • Edge clarity & colour: specify low-iron if visible edges must appear water-white.
  • Acoustic & UV performance: laminated interlayers can be tuned (e.g.
    acoustic PVB, UV-blocking PVB, coloured films).

Study Checklist (Exam Focus)

  • Memorise definitions and distinguishing traits of: Float, Clear Float (standard vs.
    low-iron), Tinted, Reflective, Decorative/Textured, Wired, Sand-Blasted/Etched, Colour-Backed, Mirror, One-Way Mirror, Laminated, Toughened, IGU, Curved, Glass Blocks.
  • Understand manufacturing sequence: batch → melt at 1500∘C1500^{\circ}\text{C} → float on tin → cooling/annealing → optional bending → edgework → optional temper/laminate → installation.
  • Be able to sketch or label typical timber vs. aluminium glazing details; point-fixed spider system.
  • Recall edge-finish terminology and when each is appropriate.
  • Recognise regulatory triggers: human impact zones, balustrades, floors, proximity to doors, wet areas.
  • Review supplier catalogues (e.g.
    Viridian, Metro, Ozone, GlassShape) for thickness limits, minimum hole spacing, maximum panel sizes.

Visual & Case-Study References (from slides)

  • Wellington Basia sand-blasted art panel (fingerprint issue).
  • "Double XQX" reflective tower (glare reflection caution).
  • Sky Tower glass floor panels (tempered-laminated composite).
  • Frameless pivot door with steel infill plates.
  • Green-toned stacked-glass interior feature wall (lecture cover photo).