Glossary

Glass Glossary

Alphabet Order
[ A ]
[ B ]
[ C ]
[ D ]
[ E ]
[ F ]
[ G ]
[ H ]
[ I ]
[ J ]
[ K ]
[ L ]
[ M ]
[ N ]
[ O ]
[ P ]
[ Q ]
[ R ]
[ S ]
[ T ]
[ U ]
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[ W ]
[ X ]
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	Category
	State of Glass
	Shape,Feature & Manuf. Process
	Usage
	Property

State of the Glass

Glass	An amorphous solid having a glass transition temperature. Ordinarily an inorganic product of fusion that has cooled to a rigid condition without crystallizing.
Glass-Ceramics	Solid material, partly crystalline and partly glassy formed by the controlled crystallization of a glass.
Modified	A glassy material that is produced by the modification of glass by means of physical and/or chemical treatments.
Composite	Composite composed of glass and other materials.
Thin Film	A thin glassy coatings on substrate.
Non-vitrified	A chemical composition with which a batch is experimentally verified not to form glass.
Melt	A high-temperature liquid of inorganic-material-related glass of which solidified body at low temperatures is not always glass.

Shape, Feature & Manufacturing Process

Frit	A powder glass that has been melted and quenched in water or air, followed by grinding or milling. It is frequently used for printing ink, glazing or sealing.
Bead	A small spherical grain of glass.
Balloon	A small spherical hollow glass.
Flat Glass	A general term covering sheet glass, plate glass, float glass, and various forms of rolled glass.
Plate Glass	Flat glass formed by a rolling process, ground and polished on both sides, with essentially plane and parallel surfaces.
Sheet Glass	Flat glass made by continuous drawing.
Cellular Glass	A thermally insulating material consisting of a high volume fraction of gaseous inclusions distributed throughout a glass matrix.
Foam Glass	The same material with ‘cellular glass’.
Anisotropic	A glass which dose not exhibit the same properties in all directions with reference to light, thereby resulting in more than one refractive index.
Graded Index	A glass having a refractive index distribution of a specified profile from surface to body.
Sintered	Glassware fabricated by fusing glass particles.
Molded	Glass that is formed in a mold.
Casting	The process of shaping glass by pouring the molten material into or onto molds, tables or rolls.
Low-melting	Glass exhibiting viscous flow below at 600 C.
Hard Glass	1)A glass of relatively high viscosity at elevated temperatures. 2)A glass with a high softening point. 3) Commonly refers to a glass that is difficult to melt.
Low Alkali	A glass containing alkali oxide of less than 5 mass%.
Mixed Alkali	A glass containing multiple kinds of alkalis.
Tempered	A mechanically strong glass which is prestressed by physical or chemical treatments.
Strengthened	The same meaning with ’tempered’.
Leached	A residual glass dissolved soluble components from a glassy material by reaching with acidic solution.
Doped(Stuffed)	A material doped some components into porous glass from solution, or penetrated some components from the surface into the body by ion beams.
Machinable	A glass that is easy to shape by machining, such as drilling or cutting.
Photochromism	A phenomena in which a material darkens up on exposure to light, but returns to its original color and original clearness under dark conditions.
Phototropy	The same phenomena with ‘photochromism’.
Sol-Gel	A glass-making process involving the gelation of sol, followed by drying and sintering. A mixture of metal alcoxides, solvent and catalysis is typical starting material of sol.
CVD	Abbreviation for chemical vapor deposition. A preparation process of coatings on a substrate by the pyrolitic deposition of a gas phase.
PVD	Abbreviation for physical vapor deposition. A preparation process of coatings on a substrate involving vacuum deposition and sputtering.
Crown Glass	(1) Soda-lime glass. (2) A type of window glass shaped by whirling a large glass sphere to form a flat circular disk with a lump in the center formed by the glassblower’s rod. (3) Abbreviation of optical crown glass.
Crystal Glass	A colorless, highly transparent glass used for art and tableware.
Flint Glass	(1) A heavy, colorless, brilliant lead-bearing glass. (2) Abbreviation of optical flint glass. (3) A clear colorless soda lime glass used for bottle or tableware.
Lead Crystal Glass	A heavy, highly transparent and brilliant silicate glass containing lead oxide more than 24 mass%. The glass is used for tableware, especially for cut glass.
Optical Flint Glass	Any optical glass of high refractive index and high dispersion, having an Abbe’s value of less than 50.0, or an Abbe’s value between 50.0 to 55.0, and a refractive index less than 1.60.
Optical Crown Glass	Any optical glass of low refractive index and low dispersion, having an Abbe’s value of at least 55.0, or an Abbe’s value between 50.0 and 55.0, and a refractive index grater than 1.60.
Soft Glass	(1) A glass having a relatively low softening point or a high thermal expansion coefficient, or which is easy to melted. Typically soda- lime glass. (2) A glass which is easily scratched or abraded.
Porous Glass	A glass filled with continuous micropore.

Usage

Wavelength Selector	An optical component of glass by which light of specified wavelength is chosen as transmitted light or reflected light.
Radioactive Waste Solidification	A vitrification process in which radioactive components in radioactive waste are mixed with glass-forming constituents and the mixture is then melted to be made into glass form for disposal.
Molded Lens	An optical glass lens formed in a mold without polishing.
Isolator	An optical component for a one-way optical path using polarizers.
Polarization-Maintaing Fiber	An optical fiber in which polarized light propagates in a specified direction.
Fiber Array	An optical device made by fusing a number of optical fibers followed by polishing. Image propagation is enable using this device.
Optical Modulator	An optical device capable of light beam deflection.
Erasable	A memory media capable of memory erasure.
Hermetic Seal	A glass-sealed component which is completely gas-tight.
Ion Electrode	A device for measurement of ion concentration having a thin separation membrane. A glass electrode for pH measurement is a typical device.

Property

Strength of Glass	Glass failure always results from a tensile component of stress. The breaking stresses of glass are far from uniform. They depend on the method of manufacturer and on the subsequent history, even if a glass with a fire-polished surface is very strong.
Abraded Strength	Breaking stress of glass measured after a processing of controlled abrasion. This is used to determine the strength for practical use.
Static Fatigue	The decrease in the breaking stress of glass with increased duration of load under conditions of static loading.
Dynamic Fatigue	Decrease of the breaking stress of glass with increased duration of load under cyclic loading conditions.
Stress Relaxation	The phenomena in which the stress in glass decreases with time due to the thermal effect.
Machinability	The ease with which a material can be machined by the process such as cutting or shaping.
Liquidus Temperature	The maximum temperature at which equilibrium exists between a molten substance, such as glass, and the primary crystalline phase.
Crystallization Temperature	The temperature at which glass is heat-treated for crystallization, or the temperature detected by DTA at which a crystal begins to crystallize.
Melting Temperature of Crystal	The temperature detected by DTA at which a crystal begins to melt.
Phase Separation	The phenomena in which a melt separates into two liquids with different chemical composition.
Expansion Coefficient	The tangent of the linear thermal expansion curve at a specified temperature, or the tangent of the linear thermal expansion between two specified temperatures.
Melting Temperature	An arbitrarily defined reference point used for comparison purposes at which the glass viscosity is 100 dPa.s. (ASTM C162) The same temperature with ‘melting point’.
Melting Point	The range of furnace temperatures within which melting takes place at a commercially desirable rate, and at which the resulting glass generally has a viscosity of 10^1.5 to 10^2.5 dPa.s. For purposes of comparing glasses, it is assumed that glass of melting temperature has a viscosity of 10² dPa.s.(ISO 7884-1)
Working Range	The range of surface temperature in which glass is formed into ware in a specific process. For comparative purposes, when no specific process is considered, the working range of glass is assumed to correspond to a viscosity range from approximately 10³ to 10⁸ dPa.s. (ISO 　7884-1).
Working Point	The temperature corresponding to a viscosity of 10⁴ dPa.s. (ISO 7884-1)
Softening Point	The temperature at which a glass fiber suspended in a furnace elongates at a specified rate under its own weight during heating. The viscosity at the softening point corresponds to a viscosity of 10^7.6 dPa.s which depends on the density and the surface tension of the glass.
Littleton Point	The same temperature with ‘softening point’.
Deformation Point	The temperature at the maximum peak of the thermal expansion curve of glass. This temperature depends on the measurement method of thermal expansion.
Dilatometric Softening Point	See ‘deformation temperature’.
Annealing	A controlled cooling process for glass, designed to reduce the thermal residual stress to a commercially acceptable level, and, in some cases, to modify the structure.
Annealing Range	The range of glass temperature in which stress in glass can be released at a commercially practical rate. For purposes of comparing glasses, the annealing range is assumed to correspond with the temperature between the annealing point and the strain point.
Annealing Point	At this temperature, the internal stresses of glass are substantially released in a matter of minutes. The viscosity corresponding to this temperature is 10¹³ to 10^13.5dPa.s and is dependent on the measurement method.
Glass Transition Temperature	The temperature, Tg at which glass transforms from an elastic to a viscoelastic material on heating, characterized by the onset of a rapid change in some specific mechanical or thermal property. Observed Tg can vary significantly depending on the property chosen for observation and the experimental technique. Typical methods are dilatometry and DTA.
Tg (Dilatometric)	The glass transition temperature determined by means of the thermal expansion curve.
Tg (DTA)	The glass transition temperature measured by DTA or DSC(differential scanning calorimetry).
Transformation Temperature	The same meaning with 'glass transition temperature’.
Strain Point	At this temperature, the internal stress of glass is substantially released in a matter of hours. The viscosity corresponding to this temperature is 10^14.5to 10¹⁵ dPa.s which is depend on measurement method.
VFT Equation	Abbreviation for Vogel-Fulcher-Tammann equation. The same equation with 'Fulcher equation'.
Fulcher Equation	According to Fulchcr, the viscosity-temperature relationship is conveniently described by the following equation; log (viscosity) = A + B/(T - To) where T is temperature and A, B and To are constants. These constants can be determined using 3 viscosity data. However, the data in the annealing range should not be used.
Arrhenius Equation	The temperature dependence of the diffusion coefficient or the electrical conductivity, k, is expressed by the equation, k = Aexp( －E/RT), where A, E, R and T are a constant, an activation energy, the gas constant and the absolute temperature, respectively.
Ion Exchange	The phenomena by which ions in glass are replaced with other ions in surrounding medium (e.g. molten salt) outside of the glass. The major species relating to the exchange are monovalent positive ions such as alkali ions.
Meltability	The easiness of melting a glass batch.
Abbe value	The reciprocal dispersive power, a value used in optical design, expressed mathematically as: Abbe value = (n_d - 1)/(n_F - n_C), where n_d, n_F and n_C are the refractive indices for the helium line at 587.6 nm, and for the hydrogen line at 486.1 and 656.3 nm, respectively.
Sellmeier Formula	The equation that expresses the dependence of the refractive index on the optical wavelength, n² = 1 + A₁L²/(L² - B₁) + A₂L²/(L²- B₂)+ A₃L²/(L²-B₃), where n and L are the refractive index and optical wavelength, respectively, and A₁, A₂, A₃, B₁, B₂ and B₃ are constants.
Dispersion Formula	The equation that expresses the dependence of the refractive index on the optical wavelength, n² =A₀ + A₁L² + A₂L^-2 + A₃L^-4 +A₄L^-6 + A₅L^-8, where n and L are the refractive index and optical wavelength respectively, and A₀ , A₁, A₂, A_3,A₄, and A₅ are constants.
Dispersion	Variation of refractive index with optical wavelength.
Total Dispersion	The same meaning with ‘mean dispersion’.
Main Dispersion	The same meaning with ‘mean dispersion’.
Mean Dispersion F-C	The refractive index difference from the F line (486.1 nm) to the C line (656.3 nm) of the spectrum, (n_F － n_C).
Relative Partial Dispersion	The Ratio of the dispersion for optical wavelength x and y to mean dispersion which is expressed as P_x,y= (n_x-n_y)/(n_F-n_C), where n_x, n_y n_F andn_C are the refractive indices for the optical wavelength x, y, c and y.
Stress Optical Coefficient	This coefficient is used for the determination of the internal stress of glass converted from the optical path difference measured by a photoelastic technique.
Transmittance	The ratio of transmitted light energy to incident light energy, T. In the case of perpendicular incident light to a flat glass surface, T is expressed by the following formula, T=(1-R)²exp(-ax), where R is the reflectivity, a is the absorption coefficient, and x is the thickness of the flat glass, respectively.
Optical Absorbance	The light intensity ratio, I/Io, where Io and I are intensity of the incident light and that of the transmitted light through a medium, respectively.
Optical Density	D = -log(I/Io) , where Io and I are the intensity of the incident light and that of the transmitted light through a medium, respectively.
Internal Transmission	Transmission of light in a glass body without consideration of surface reflection.
Reflectance	The ratio of reflected light to incident light, r. For perpendicular incident light, r=((n-l)/(n+l))², where n is the refractive index of the glass.
Optical Absorption Edge	In a continuous optical spectrum, the optical wavelength at a range longer than that at which optical absorption steeply decreases.
Optical Gap	The photon energy, Eg, of Eg=hc/L where L is the wavelength of optical absorption edge, h is Plank’s constant and c is the light velocity.
Numerical Aperture	A number, NA, related to the critical angle (a) of a cone of incident light to an optical fiber. When the refractive index of the core and the cladding of the fiber is n_i and n_o,respectively, then NA = sin a =(2n_i(n_i- n_o))^1/2.
Electric Conductivity, E and So	See Arrhenius equation. The electrical conductivity S is expressed by the equation, S = S_oexp( －E/RT).
DC Volume Resistivity E and r_o	See ‘Arrhenius equation’. The electrical resistivity r is expressed by the equation, r = r_oexp(E/RT).
AC Volume Resistivity E and r_o	See ‘Arrhenius equation’. The AC volume resistivity r is expressed by the equation, r = r_oexp(E/RT).
Chemical Durability	The lasting quality (both physical and chemical) of a glass surface. It is frequently evaluated after prolonged contact with water, chemicals or atmosphere in terms of chemical and physical changes in the glass surface, or in terms of changes in the contents of a vessel.
Additivity Relationship	Many glass properties (P) obey the following linear relationship. P = p₁a₁ + p₂a₂..+ p_na_n, where p_i is the additivity factor for the i'th component, and a_i is the content of the i'th component in mass%, mol% mass fraction or mol fraction. Note that a₁ + a₂..+a_n = 100 % or 1.
Dissipation Factor	The same meaning with ‘loss tangent’.
Loss Factor	The same meaning with 'loss tangent'.
Tangent Delta	The same meaning with 'loss tangent'.
Standard Spectral Lines	The characteristic narrow optical spectral lines used for the measurement of the optical constants of optical materials. The name, the optical wavelength, the light source and the color of each spectral line is shown in the following table.
	Notation	t	s	r	C	C'	D	d
	Wavelength /nm	1013.98	852,11	706.52	656.27	643.85	589.24	587.56
	Light source	Hg v	Cs v	He v	H	Cd v	Na v	He
	Color	IR	IR	red	red	red	yellow	yellow
	Notation	e	F	F'	g	h	i
	Wavelength /nm	546.07	486.13	479.99	435.83	404.66	365.01
	Light source	Hg v	H	Cd v	Hg v	Hg v	Hg v
	Color	Green	blue	blue	blue	violet	UV

Diffusion Coefficient Equation	See Arrhenius equation. The diffusion coefficient D is expressed by the equation, D = D_oexp( －E/RT).
(Linear Thermal) Expansion Coefficient	Tangent of linear thermal expansion curve at certain temperature.
Transformation Point	The same meaning with ‘glass transition temperature’.
Weathering	A phenomena in which the surface of glass deteriorates by the effect of the atmosphere, usually by the humidity.

Alphabet Order