Glossary of Terms

A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z

A

Annealing

In the manufacturing of float glass, it is the process of controlled cooling, which is done in a lehr to prevent residual stresses in the glass.

Annealing Lehr

An apparatus used as a controlled heating/cooling instrument.

ASTM

American Society for Testing and Materials

Autoclave

A vessel that employs high pressure heat used to produce a bond between glass and PVB or urethane sheet, creating a laminated glass product.

B

Bent Glass

Flat glass that is curved into shapes while still hot.

Beveling

The process of edge finishing glass to a beveled angle.

Blemish

A noticable impefection in glass.

Blisters

Bubbles in a coating film that forms during the heat treating process.

Bow (or Warp)

A curve, bend or other deviation from flatness in glass.

Break Pattern

The resulting pattern formed by the cracks in glass when broken. Also called the fracture pattern.

Breather (Tube) Units

An insulating glass unit with a tube in the unit's spacer to accommodate pressure differences in shipping, due to the change in elevation. These tubes are sealed at the jobsite prior to unit installation.

Bubbles

A gas pocket in the interlayer material or between the glass. In float glass, a inclusion greater than 1/32" in diameter.

Bulb Edge

The extreme lateral edge of the ribbon, as drawn in the float glass manufacturing process.

Bullet Resistant Glass

The multiple lamination of glass. Glass and plastic that are designed to resist penetration from small fire arms.

Butt Glazing

The installation of glass where the vertical glass edges are without structural supporting mullions.

C

Capillary Tube Units

(See Breather Tubes)

Case Hardened

A term sometimes used for tempered glass.

Center Tension

Tension stresses within the center portion of heat-treated glass.

Ceramic Enamel

An inorganic and non-metallic coating used to be fused to a substrate.

Checks

Very small cracks in flat glass usually at the edge.

Chemically Strengthened Glass

Glass that has been heat treated from ion-exchange to produce a compressive stress layer at the treated surface area.

Chip

An imperfection due to breakage.

Condensation

Moisture on the surface of an object caused by warm moist air coming into contact with a colder surface.

Crown Process

A method of making flat glass. Blowing a large bulb, opening it up, and spinning it flat.

Crush

A lightly pitted area on the glass surface, resulting in a dull gray appearance.

Cullet

Broken glass, extra glass from a previous melt or the edges that are trimmed off glass to size. Cullet is one of the essential ingredients in the raw batch in glass-making, it facilitates the melting process.

Cut Size

Glass cut to a specified width and length.

Cutting

Scoring glass with a diamond, steel wheel or other alloy wheel and breaking it along the score.

Cylinder Process

A manufacturing process of flat glass. Molten glass is blown and drawn into the form of a cylinder, which is subsequently split longitudinally, reheated, and flattened.

D

Deflection (Framing Member)

The amount of bending movement of any part of a structural member perpendicular to the axis of the member under an applied load.

Deflection of Glass

The amount of bending of the center of glass.

Design Pressure

Specific pressure a product is designed to withstand.

Dice

The cubical pattern of a fracture in fully tempered glass.

Diffusing

The scattering and dispersing and the tendency to eliminate a direct beam of light.

Digs

Deep, short scratches.

Dirt

A small particle of foreign material imbedded in the surface of flat glass.

Distortion

Alteration of viewed images, caused by the variations in the flatness of glass.

Double Glazing

Two lites of glass, separated by an air space, to improve insulation against heat transfer and sound transmission. Insulating glass units contain air between the glass which is thoroughly dried and sealed, eliminating condensation and providing superior insulation.

Double Glazing Unit

Two panes of glass separated by a permanently sealed air or gas cavity.

Double Strength Glass

Float glass, approximately 1/8" (3mm) thick.

Drawn Glass

Glass produced by a continuous drawing operation.

E

Edge Compression

Compressive stresses at the edge of heat-treated glass.

Edge Finish

A specified finish to the edges of glass. Sometimes called Edgework.

Edging

Grinding the edge of flat glass to the desired shape or finish.

Emissivity

The measurement of a surface's ability to emit long-wave infrared radiation.

Etch

To alter the surface of glass. Usually by hydrofluoric acid or other caustic sources. Permanent etching of glass can occur from long term, high alkali contact.

F

Fabricating Debris

Any debris resulting from the processing and fabricating of glass prior to the tempering process.

Fenestration

Any glass panel, window, door or skylight on a building.

Flat Glass

A term that describes float glass, sheet glass, plate glass, cylinder and rolled glass.

Float Bath

A pool of molten metal, usually tin, in which molten glass is drawn into a flat sheet.

Float Glass

Glass formed on a bath of molten tin. The surface in contact with the tin is known as the tin surface. The top surface is known as the air surface.

Flux

An ingredient that reduces batch melting temperature.

Frit

Glass in particulate form.

Frosted

Surface treated to simulate frost.

Fully tempered glass

Flat or bent glass that has been heat-treated to a high surface and edge compression to meet ASTM C 1048 Standards. Fully tempered glass, if broken, will fracture into many small cubical pieces, known as diceing. Fully tempered glass is approximately four times stronger than annealed glass of the same thickness.

G

GANA

Glass Association of North America.

Gas-Filled Insulated Glass Units

Insulating glass units with a gas in the air space to increase the unit's sound and insulating valve.

Gaseous Inclusion

A round or elongated bubble in glass.

Glass

A hard brittle substance, usually transparent, made by fusing silicates, soda ash and lime stone, under high temperatures.

Glazing

A general term used to describe glass, panels, etc. Also the process of installing glass or panels into a prepared opening in windows, door panels, partitions, etc.

Glazing Select Quality

This represents the float glass supplied when quality is not otherwise specified. (Typically q^3 from ATSM C 1036 Standard.)

Gloss

The degree of shine or luster on the surface of glass, ceramic enamel or ink.

H

Heat-Absorbing Glass

Glass that absorbs a significant amount of solar energy.

Heat-Resisting Glass

Glass able to withstand high thermal shock, usually because of its low coefficient of expansion.

Heat-Strengthened Glass

Flat or bent glass that has been heat-treated to a specific surface and edge compression to meet the requirements of ASTM C 1048. Heat-strengthened glass is approximately two times as strong as annealed glass of the same thickness. Heat-strengthened glass is not considered safety glass, because it will not dice like fully tempered glass.

Heat-Treated

Term used for both fully tempered glass and heat-strengthened glass.

Hot End

Those manufacturing operations dealing with hot glass, which are melting, forming, and annealing.

I

Inclusion

A foreign solid or gas within the glass matrix.

Insulating Glass Unit

Two or more pieces of glass spaced apart and hermetically sealed to form a single-glazed unit, with an air space between each lite. Commonly called IG units.

Interlayer

Any material used to bond two lites of glass together to form a laminate.

Iridescence

A display of rainbow-like colors in glass.

IWCA

International Window Cleaning Association.

J
K

Kink

An abrupt deviation on flat glass most commonly found near the edge of heat-treated glass.

Knot

An imperfection in the form of a vitreous lump.

L

Laminated Glass

Two or more pieces of glass permanently bonded together with interlayers.

Leaded Glass

Pieces of glass bonded together at their edges. Usual with soldered lead.

Lehr

A long, tunnel-shaped oven for annealing glass, usually by a continuous process for slow cooling.

Lime

Calcium oxide or a mixture of calcium oxide and magnesium oxide.

Limestone

Calcitic limestone or dolomitic limestone.

Lite

Another term for a pane of glass.

Low-emissivity or Low-e

A low rate of emitting absorbed radiant energy.

M

Melting furnace

The glass melting assembly, including the melter, regenerators, flues, refiners, forehearths, channels, throats, etc.

Migration

Spreading or creeping of a compound into adjacent surfaces.

Muntins

Horizontal or vertical bars that divide the glass area into smaller lites of glass.

N

NGA

National Glass Association.

O

Open Bubble

A surface cavity formed by a gaseous inclusion.

Orange Peel

Roughness or waviness on the surface of glass which resembles the skin of an orange in texture.

P

Patterned Glass

Rolled glass with a pattern imprinted on one or both sides. Usually used for light control on bath enclosures or decorative glazing.

Pilkington Float Glass Process

The process of making flat glass with a continuous pour of glass onto a molten tin bath.

Pittsburgh Sheet Process

The method of making sheet glass by drawing it vertically upward from a bath.

Plate Glass

Flat glass formed by the rolling process, then ground and polished on both sides.

Polariscope

A device for examining the amount of strain in a glass sample.

Pyrolytic Coating

A thin Low-e coating applied to the hot surface of glass when manufactured.

Q

Quality

A relative term describing the degree of excellence with regards to a product, process or service.

Quench

To rapidly cool.

Quench Marks

A pattern of dark shadows commonly refered to as the Quench Pattern.

R

R-Value

The thermal resistance of a glazing system.

Raw Batch

A glass batch without cullet.

Raw Cullet

A glass batch made of only cullet.

Reflective Glass

Glass with a metallic coating to reduce solar heat gain.

Ribbon

A continuous length of glass in process.

Roller Distortion or Roller Wave

A waviness resulting in horizontal heat-treated glass, as a result of glass being transported through the furnace on rollers.

Rough Opening

The opening in a wall in which a door or window is installed.

Rub

Small scratches in glass, generally caused during shipping.

S

Safety Glass

Flat or bent glass that is heat treated or laminated, and if broken would not cause serious injury.

Score

To penetrate the surface of glass with a cutting device, such as a glass cutter.

Scratch-Resistant Coating

Coating applied to glass surfaces to reduce scratching effects.

Scratches

Any marking or tearing of the glass surface.

Sealed Insulating Glass Units

(Same as "Insulating Glass Unit")

Seam

To grind or sand the sharp edges of a piece of glass, usually with a belt or wheel.

Seeds

Small bubbles in float glass, less than 1/32" in diameter.

Shadowgraph

A devise used for inspecting glass for distortion or other defects.

Sharks Teeth

A term used to identify the appearance of the cut edge of glass.

Sheet Glass

Flat glass made by continuous drawing in the vertical direction.

Shore "A" Hardness

Measurement of hardness by means of a Durometer Hardness Gauge.

Silvering Process

The process of appling silver to the back of mirrors.

Sizing Glass

To cut a piece of glass to a specific size.

Skylight

A glass or plastic window, usually installed on a roof of a building.

Smoke

Streaked areas in glass appearing with slight discoloration.

Soda

Sodium oxide. A carbonate of sodium.

Soda Lime Glass

An abbreviation for soda-lime-silicate glass.

Soda-Lime-Silicate Glass

Glass compositions in the most common flat glass made today.

Solar Control Glass

Tinted or coated glass that reduces solar heat gain through a glazed product.

Spandrel

Panel of a wall located between vision areas which conceal structural columns, floors and walls.

Stain

Discoloratin of glass.

Stones

Crystalline inclusion imbedded in the glass.

Storm Window

A glass panel placed on the outside of an existing window as an extra protection from the elements.

Strain Pattern

A specific iridscent pattern or darkish shadow that appears under certain polarized lighting conditions, also known quench marks. The stress pattern is caused by localized stresses from the rapid air cooling on a tempering operation, such as heat-treated glass.

Strength

A term to indicate relative thickness in flat glass.

Strength, Double

Flat glass between 0.115 and 0.134 in. thick.

Strength, Single

Flat glass between 0.085 and 0.101 in. thick.

Stress (Residual)

Any tension or compression existing in the glass, usually as a result of incomplete annealing.

String

An imperfection in glass resulting from a large grain of sand or foreign material.

Suction Process

A process in which glass is transported or installed by vacuum.

Surface Compression

Surface stresses in heat-treated glass, resulting from rapid cooling of glass surface to produce compresssive stresses at the surface.

T

Tear

An small imperfection in the surface of glass.

Temper

The amount of residual stress in annealed glass.

Tempered Glass

A term for glass subjected to heat treatment, followed by rapid cooling, to produce a compressive surface layer.

Tension

The inner layer of heat treated glass.

Thermal Endurance

The ability of glass to withstand thermal shock.

Thermal Shock

The change in temperature, sometimes caused by a shadow, imposed on a glass surface.

Thermal Stress

The stress produced by the change in temperature within a glass body.

Tong Marks

Small, surface indentations along one edge of vertically-tempered or heat-strengthened glass, resulting from the tongs used to transport the glass through the heat treating process.

Toughened Glass

A term sometimes used by foriegn manufactures to identify heat-treated or fully tempered glass.

Tweel

A furnance door that opens vertically.

U

U-Value

The measurement of heat transmission due to the thermal conductance.

V

Vinyl Windows

Windows holding glass in place with extruded vinyl.

W

Water Glass

Sodium silicate glass that is soluable in water.

Weeps or Weep Holes

Drain holes or slots in the framing of windows to prevent accumulation of condensation or water.

Window

An opening constructed in a wall to admit light or air, usually framed with glass and sometimes mounted to permit opening and closing.

Wired Glass

Flat glass with wire mesh embedded in the glass.

X
Y
Z
GLASS RESTORATION

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