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Glass Glossary


ACL - (Applied Ceramic Labeling) Colored Lettering or design of a ceramic nature fused onto bottles.

Amber - A brown color of glass that absorbs nearly all radiation with wavelengths shorter then 450 mm. Amber glass offers excellent protection from ultraviolet radiation. This is critical for products such as beer and certain drugs. Example of amber glass can be found on the amber glass page.

Annealing - A controlled heating and cooling process designed to relieve internal stresses introduced in a glass container during and immediately after glass container formation.

Annealing Point - The temperature at which internal stresses in glass are significantly reduced. In the annealing operation, glass is gradually cooled from above the annealing point temperature to below the strain point temperature. This slow cooling relieves residual thermal stresses that would develop if the glass were allowed to cool in an uncontrolled manner.


Batch - The mixed raw materials used in manufacturing glass that have been blended and proportionally mixed for delivery to the glass furnace.

Blank - Usually refers to a glass parison that is formed during the first step of glass molding. The piece is then transferred to a lamp worker or glass blower for final shape configuration.

Blank Mold - The metal mold in which the parison is formed.

Blister - A gaseous inclusion or bubble in the glass.

Blow Mold - Usually a metal mold used to form a piece of glass from a hot gob.

Blow Process - A method of glass container manufacturing of narrow finish containers in which the parison is formed by compressed air.

Borosilicate Glass - A high silicate glass that has at least 5% boron oxide.

Bottom Plate - A piece of mild equipment used to shape the bottom of the glass container. It can have depressions in where letters and symbols are formed in the glass to indicate the cavity number and or manufacturer of the particular container.


Caps - A term used for metal or molded closures

Chemical Durability - The resistance of glass to attack by solvents or products.

Closure - Any structure or device, which is designed to close off the opening of a container and prevent loss of its contents. Check out the cap/closure page for more example of closures.

Cobalt Glass - Blue colored glass obtained by the use of cobalt oxide. Examples of cobalt glass can be found on the cobalt glass page.

Continuous Thread (CT) - A continuous spiral protecting glass ridge on the finish of a container intended to mesh with the thread of a screw type closure.

Contraction Coefficient - The fractional change in length of a piece of glass per degree change in temperature on cooling from the annealing point to ambient temperature.

Cullet - Waste or broken glass. Clean cullet is always used in the batch.


Density - Mass per unit volume measured in grams per cubic centimeter.

Distribution - The wall thickness or the evenness of the glass distribution throughout the container.


Ear - The name given to the finger grip of pressed glass between the shoulder and finish of a 1/2 gallon, gallon, or other glass jug. The ear is used to facilitate holding the jug.

Etch - To attack the glass surface with a strong chemical agent, usually hydrofluoric acid. Usually used in decorating glass.


Fill Point - The level to which a container must be filled to furnish designated quantity of contents.

Finish - The part of a bottle which holds the cap, stopper or closure. The area that has the threads (generally a shortened term for thread finish). The first part made on an automatic machine, but the last part (or finish) to be made when bottles were hand blown. On lab ware, may refer to an interchangeable ground joint.

Flint - A glass color or lack of color. Flint is perfectly clear transparent glass, like window glass, used for all types of containers.

Forming - The shaping of hot glass.

Forming Molds - The forming mold sometimes referred to as the bottle mold is the mold in which the bottle is blow into its final shape after being preformed in a blank mold.


GPI - Glass Packaging Institute. An organization composed of glass container producers. GPI establishes policies, such as standardization and developed and develops industry-advertising programs.

Glass - An amorphous, artificial, non-crystalline substance made by fusing some form of silica and alkali and sometimes another base such as lime.

Glassblowing - The shaping of glass using air pressure.

Gob - A portion of hot glass that is delivered from the furnace for forming

Grossage - A quantity in terms of gross. Grossage is the usual denomination used in glass container terminology.


Hard Glass - A glass with a high softening point or high viscosity (usually borosilicate).

Head Space - The space between the level of the contents in the neck of a container and the closure. Head space is intended to furnish room for expansion of product due to heat or other action after packaging.

Hot End - A manufacturing term for the area of a glass manufacturing plant where molten glass is processed.


IS Machine - A term is short version of "Individual Section Machine". The IS machine is used for the information of glass container. It has the ability to have one or more sections taken out of production for maintenance purposes while the remaining sections continue making containers.


Lampworking - Flame re-working of a blank or tubing cane, typically on a lathe.

Lehr - A long belt-fed, tunnel-shaped oven used to heat glass to the annealing point and then slowly cool it to room temperature to remove any residual thermal stresses in the glass. Can also be a large oven where glass is manually loaded and unloaded (batch lehr).

Linear Coefficient of Expansion - The fractional change in length of a piece of glass per degree change in temperature. The coefficient of expansion generally indicates the thermal endurance of the glass. Glasses with a low linear coefficient of expansion can be subjected to greater rapid temperature changes with less chance of fracture than glasses with a high coefficient of expansion. (Generally, Type I glasses have a lower COE than Type III).

Lug Finish - A glass container finish identified by horizontal tapering protruding ridges of glass that permit the specially shaped edges of the closures to slide between the protruding lugs and fasten securely with a partial turn.


Melt - The amount of glass that is melted at one time.

Meniscus - The curved surface of the liquid at the fill pint of a bottle where the fluid level next to the glass is higher then in the center.

Mold - A set of iron forms fastened on a bottle machine to provide a means of shaping a glass container. Parts of the set are tops, neck rings, blank molds, finish molds, and bottom plates with a plunger used in producing wide mouth container.

Mold Mark - The mark in the bottom of the container that denotes the manufacturer.


Narrow Mouth - The finish of a glass container in which the diameter is small relative to the diameter of the body.

Neck - The portion of a glass container in which the shoulder cross sectional area decreases to join the finish.

Neck Bead - A small protruding circle of glass on a glass container at the point where the neck meets the finish of the container

Neck Bead Ring (Or Band) - A protruding ring just above the neck ring parting line necessary in the manufacture of glass container and specifically in transferring containers from blank to mold.

Neck Ring - A piece of mold equipment used to form the finish of the glass container.


Overflow Capacity - The capacity to the top of the finish or to the point of overflow.


Parison - The preliminary shaped red-hot glass that hangs from the neck rings as the blank molds open. The parison is also called "pattern" or "blank".

Parting Line (glass) - The slight horizontal ridge formed by a surplus of glass blown into a worn crevice or joint between two parts of the mold equipment. These lines may occur on carious areas of the container. Such as between the neck ring and the plunger tip or guide ring, between the neck ring and blank or mold, and between the mild and bottle plate. The vertical line formed by the joint between two halves of the same mold part is called a "seam".

Pour out Finish - A glass container finish, with an undercut immediately below the top, design to facilitate pouring without dripping. The pour out finish is used principally for prescription and other drug and chemical containers.

Press & Blow Process - A method of glass container manufacturing of large diameter finish containers in which the parison is shaped by pressing the glass against a blank mold with a metal plunger.

Pressed Glass - Glassware that is formed by pressing a gob between a mold and a plunger.


Sealing Surface - The top portion of the finish, which make contact with the sealing gasket or liner and forms a seal.

Shoulder - The portion of a glass container in which the maximum cross section or body area decreases to joint the neck of the container.

Silica - Mineral with many cryptocrystalline varieties (quartz, rock crystal, amethyst, etc.) and amorphous.

Soda - Soda hydroxide, white glassy solid material very soluble in water and alcohol. It is obtained by the dissolution of sodium chloride by electrolysis.

Soda-Lime (or Soft) Glass - A glass with a substantial portion of lime in the formula.

Softening Point - Temperature at which a thread or rod of glass rapidly deforms under its own weight.

Strain Point - The temperature at which thermal residual stresses become permanent upon cooling. Temperatures above the strain point will introduce permanent stresses that can cause or contribute to fracture. At temperatures below the strain point, the glass can be temporarily heated and cooled without introducing permanent stress. The strain point can be considered the maximum service temperature.


Tank - The furnace that melts the raw materials into molten glass. Temperatures in the tank vary depending on the glass type being melted, but are typically in excess of 1,200°C.

Temper - The degree of residual stress in annealed glass as measured using polarized light techniques.

Tolerance - The allowable variation from actual specifications permitted in the manufacturing operation.

Type 180 Glass - Glass This glass is an exceptionally clear borosilicate glass of high chemical durability, which has been especially formulated for the lowest background count while still at a reasonable cost. Great care has been taken to select only those ingredients for the batch that would not cause unwanted background count or color. Potassium as a separate element has been excluded from the batch to minimize K40. Special controls assure high quality and batch-to-batch uniformity.

Type 200 Glass - Glass, low extractable borosilicate glass, is a clear borosilicate glass with exceptional thermal endurance that meets the requirements for both USP and ASTM Type I, Class A, borosilicate glass.

Type 300 Glass - Glass is a chemically resistant clear borosilicate glass that meets all of the requirements for Type I glass as specified in the current revision of the U.S. Pharmacopeia.

Type 320 Glass - Glass is a similar composition to "300" except amber color for light sensitive applications. Meets UV light protection limits as specified in the current revision of the U.S. Pharmacopeia.

Type 400 Glass - Glass is a clear borosilicate glass that falls well within the limits for Type I chemically resistance borosilicate glass, as specified in the current revision of the U.S. Pharmacopeia.

Type 500 Glass - Glass is similar to the "400" formulation except amber color for light sensitive applications. Meets UV light protection limits as specified in the current revision of the U.S. Pharmacopeia.

Type 800 Glass - Glass is a superior soda-lime clear glass that meets requirements for Type III soda lime glass as specified in the current Revision of the U.S. Pharmacopeia.

Type 900 Glass - Glass is similar in formulation to "800" except amber color for light sensitive applications. Meets UV light protection limits as specified in the current revision of the U.S. Pharmacopeia

Type I Glass - Containers made of type 1 borosilicate glass are generally used for preparations that are intended for parenteral administration. Highly resistant borosilicate glass.

Type II Glass - Treated soda lime glass.

Type III Glass - Soda lime glass

Type NP Glass - General-purpose soda lime glass


Weathering - The attack on glass surface by atmospheric elements.


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