Full Antique: Term applied to art glass produced by the historical
mouth-blown cylinder method. The craftsman blows a glass cylinder
which is annealed and cooled. The cylinder is then scored lengthwise,
separated, re-heated and folded out into a flat sheet. Common
characteristics include attractive linear striations and a very pristine surface.
Drawn Antique: Also called semi-antique, machine antique or new antique.
A simulated full-antique produced by the Vertical Draw method
(see Sheet Forming Methods).
The textural striations are mechanically applied.
Quality is excellent and cost is less than full antique. GNA
(German New Antique) is a common example.
Scribed Antique: A simulated full antique produced by the Double Roll
(see Sheet Forming Methods).
The linear striations are scribed into
the hot glass surface. Quality is excellent and cost is considerably
less than full antique. Introduced by Spectrum Glass in 1996 under the
trade name Artíque®.
See Scribed Antique, above.
A machine made "reamy" glass, created by combining glasses of
mis-matched compositions. The different glasses "oppose" each other
when they are stirred together, creating artistic 3-D swirls. A Spectrum exclusive.
- Bent (or Slumped) Glass
Glass which has been heated in a kiln from room temperature to a
temperature high enough to cause it to soften and slump (sag) into or
over a mold. The finished item takes the shape of the mold.
Cold glass (usually clear, thick plate) with edges that have been
ground and polished to an angle other than 90 degrees. Transmitted
light is refracted and a prism-like effect results. Bevels are available
in a variety of sizes, shapes and geometric configurations
(called "clusters") for incorporation into leaded glass work.
A glass ingot, similar to a dalle, used in glass casting.
See Coefficient of Expansion.
Channeled strips of lead, zinc or other metal used to
bind glass pieces within a design.
(See Leaded Glass.)
Glass cylinder consisting of groups of rods of different colors,
which are bundled together and fused to form a design that is visible in cross section.
- Cast Glass
A glass art medium in which glass is melted in, or melted and
then poured into, a pre-shaped mold to create a finished project.
- Cathedral Glass
Describes transparent glass that is monochromatic—i.e.,
single color sheet glass, with smooth or textured surfaces.
(Single Roll forming method.) A surface texture resulting from the
chilling of hot glass on a cool table. The appearance is likened to the paw prints of a cat.
- Coefficient of Expansion
The ratio of the change in length or volume of a glass to its
original length or volume per unit change in temperature. Used
to help determine compatibility of different glasses for the fusing process.
and Tested Compatible.)
Paper-thin elements of glass that can be incorporated into a fused
or blown glass design. Also called "shards."
Process in which a rake-like tool is drawn across molten glass to
create artistic patterns.
Glasses are said to be compatible if, after being fused together by
blowing or kiln forming and properly annealed, they remain relatively free
from internal stress.
(See Coefficient of Expansion.)
- Copper Foil
Thin, narrow strips of adhesive-backed copper tape used to wrap the
edges of glass pieces that have been cut to fit a pattern. Once
wrapped, solder is applied, bonding the glass pieces together. Assembling
a stained glass project in this manner is called the "copper foil technique."
Louis Tiffany is credited with its development.
(Blown Cylinder method.) The hot cylinder of glass is dipped in liquid,
causing radical, random fissures in the glass. The cylinder is then
reheated and further blown to heal the surface fissures. Resulting surface
resembles the texture of alligator skin.
Thick (usually 1") slabs of cathedral glass.
- Dalle de Verre
An art glass medium in which dalles are broken into pieces with
a carbon hammer and set in an epoxy base to adhere them in a decorative
design. Dependent on large scale for best appearance, they are primarily
used in architectural applications such as church walls.
Commonly used term to describe glasses that have been coated with
one or more ultra-thin crystalline layers of transparent metal oxides designed to
enhance reflections at specific wavelengths of light. The process occurs
in a vacuum chamber at elevated temperatures. The resulting effects are
striking and brilliant color reflections at varying angles of incidence.
- Drapery Glass
Glass sheets with multiple dramatic folds, likened to those in hanging drapes.
- Expansion Coefficient
A numerical designator assigned to a glass to describe its
Coefficient of Expansion.
Glass of one color with a very thin layer of another color on one side.
Flashed glass is often used for etched or sandblasted glass art. When
sections of the thin color layer are removed, the base color shows through.
Chemical agent (liquid or paste) used to facilitate the flow of
solder and prevent formation of oxides during soldering.
Ground glass, ranging in particle size from gravel-like to a fine powder.
Frit is sometimes used as a raw material in glass manufacture, and
sometimes as a coloring agent or for decorative effect in hot glass crafts
like blowing and fusing.
- Fused Glass
Glass forms produced by placing different pieces of glass in contact
with each other in an arranged design, then firing them in a kiln at a
temperature high enough to fuse them into one piece of glass.
- Fractures & Streamers
In the single roll process
(see Sheet Forming Methods),
thin glass chips or shards (fractures) and/or glass string
(streamers) are arranged on the casting table before the glass
is poured, and thus pressed into the glass sheet as it is formed.
A texture created on the surface of cold glass by applying hot
animal glue and allowing it to dry under controlled temperature and humidity
conditions. As the glue dries and contracts, it chips the glass surface in a
natural and attractive pattern, likened to frost on a window pane.
- Gold Pink
Common name for colored glasses in the pink/cranberry/fuchsia range
that require gold oxide as a coloring agent.
- Hand Cast Sheet Glass
Sheet glass produced by the single roll method
(see Glass Sheet-Forming Methods).
Surface treatment in which a layer of metallic oxide is bonded to
the hot glass surface just after sheet-forming, resulting in a colorful, shimmering effect.
A piece of glass that has been cut and faceted or press-molded into a geometric
shape like a jewel. Often incorporated into leaded glass artwork.
- Leaded Glass
Sheet glass pieces joined with metal strips, usually made of lead,
called "came." Solder is applied to the joints of the came to bond
the work together.
Glass containing lead as a raw material (as in "leaded crystal").
Italian for "a thousand flowers." Commonly refers to glass objects made
from masses of murrini slices.
A picture or decorative design made by setting small colored pieces
of glass or ceramic material into a surface using cement or grout as
a bonding agent.
- Mottled Glass
See Ring Mottle.
A thin slice of complex glass cane that can be used as a
component in another glass object.
A fettuccini-like glass shape used as a decorative element in the hot glass arts.
(See also Studio Nuggets.)
A small, irregularly shaped "glob" of glass, flat on the bottom,
rounded across the top. Nuggets are made by literally dropping a
small amount of molten glass onto a flat surface. Frequently called "globs,"
they are often incorporated into leaded glass artwork.
- Opal or Opalescent
Said of any glass into which a material has been introduced at
the raw materials stage (usually fluorine or phosphorus) which causes a
degree of crystallization to occur, and creates opacity in the glass.
Reflected light is colorless, therefore white. The degree of opacity
(and "whiteness") is variable depending upon composition and temperatures
used in the manufacturing process. Commonly then, white glass is
Solid Color Opalescent Glass: Glass which is both colored and
crystallized, creating a single color sheet, more opaque than
a cathedral. Sometimes called "opaque" glass.
Mixed Opalescent Glass: White glass (opal) mixed with one
or more other colors to create a variegated, multi-colored sheet.
Light transmission varies with composition. Also called "variegated opalescent,"
- Painted Glass
Glass on which special paints (containing frit) have been applied in
illustration or decorative pattern and then heated in a kiln to a temperature
high enough to fuse the pigments permanently to the glass surface. The
modern version of the original medieval "stained glass."
- Pate de Verre
An art glass medium in which powdered glass frits are spread
in a decorative design, then fired in a kiln.
Descriptive of Full-Antique glass with a wavy irregular surface.
High-temperature brick used to construct ovens for melting glass.
- Ring Mottle Glass
An opalescent glass in which rates of crystal growth have been
controlled to create ring-shaped areas of opacity. The effect is a
visual surface mottling.
A surface texture, often dramatic, consisting of linear or irregular ripples.
Created naturally in some sheet-forming processes, imitated with an
embossing roll in others.
Used to describe cylindrical, pencil-thick sticks of glass used
primarily in flameworking and glass bead making. They are available in
a wide color range and many expansion coefficients.
A mouth-blown piece of glass that has been spun into a circular
shape, often irregular. Sometimes incorporated into leaded glass artworks.
Machine-made facsimiles are common, called "pressed rondels."
- Seedy Glass
Glass in which air bubbles are entrapped. Air or gas is injected into
the molten glass prior to forming the sheet.
- Slumped Glass
See Bent Glass.
A fusible alloy, usually tin and lead, used to join metallic parts,
or the act of applying it. Used to bond metals in both the leaded and
copper foil techniques of stained glass work.
- Stained Glass
Commonly used to describe any colored flat glass or any
object made of such glass joined by metal strips. The term
originally applied to colored or clear flat glass cut to fit an artist's
design, on which details were painted in pigment with a brush.
The glass pieces were then heated in a kiln or oven to bond the
pigment to the glass surface. This firing makes the painted detail as
durable and permanent as the glass itself. Most religious windows from
medieval times until this century were executed in this manner, and
so the term came to be used first for any architectural application,
and then for any design in colored flat glass. It is now universally
accepted as a convenient general term to define the art, the
craft, and the industry.
- Streaky Glass
Two or more cathedral glasses mixed together to create a
multi-colored glass sheet. Some use this term also to describe
Mixed Opalescent glass as defined above.
A spaghetti-like glass shape used as a decorative element in the hot glass arts.
- Studio Nuggets™
Uniform clear glass pellets used as a raw material in glass blowing,
glass casting, and fusing. Part of the System 96® family
of tested compatible products.
- System 96®
A broad family of Tested Compatible glass materials for the hot
glass arts. Suitable for blowing, fusing, casting, flamework, and
any combination of these media, System 96 is a partnership of
independent companies who test their products to an identical standard
to assure their compatibility.
A combination of marble, granite, onyx, or glass chips in a
binder of portland cement or other resinous material. After curing,
the surface is ground to expose the decorative chips.
- Tested Compatible
Descriptive of glasses which have been tested and marked
prior to sale to verify compatibility with each other when combined
in a hot glass process like blowing, fusing, or casting.
- Textured Glasses
Rolled textures: In rolled glasses
(see definitions below), one of the forming rolls is
embossed with a texture that is imprinted on the glass as
the sheet is formed. This produces glass smooth on one
side and textured on the other. Common examples are "hammered,"
"granite," and "muffle."
Natural textures: any textural effect created
without mechanical influence or embossed rolls. Includes Baroque
Cold glass textures: this category includes
glue chipping, etching, sand blasting, and any other surface treatment
performed on the cold glass sheet at room temperature.
A Spectrum Glass exclusive. A natural surface texture created by
stretching the hot glass sheet while it is still in a malleable state.
The result is gentle, rolling waves that resemble the surface of a
lake or stream.
A Spectrum Glass innovation. Mixed opalescent glass with only thin
wisps of white, like lazy cloud trails.
Glass Manufacturing Terms
Cooling the formed glass product at a controlled rate of
temperature change for the purpose of relieving thermal stress.
The appropriate cooling curve varies with glass type and formed
shape, especially thickness. Directly related to glass cutability.
The mixture of granular raw materials that is prepared and
put into the melting furnace to create a given glass. The primary
raw materials for clear glass are silica sand, soda ash and
limestone. Cullet is also often used.
- Continuous Furnace
A glass melting furnace which is continuously full of molten
glass. The introduction of batch (raw materials) into the furnace
displaces existing molten glass and forces it out of the furnace
and through the forehearth to the forming process. The process
continues for the life of the furnace.
(See Process Diagram.)
Crushed glass scraps, generally created as a by-product in glass making, can also be crushed glass specifically produced per a customer's request. Some glass makers use cullet from other sources or from glass recyclers as a major raw material in their own batches.
- Day Tank
A glass melting furnace that is designed to operate on a 24-hour
cycle. The batch is added to an empty furnace at a rate that
allows it to melt properly, until the furnace chamber is full. Then, after
suitable "cookout" has occurred, the molten glass is used to make
product. When the furnace is empty, the cycle is repeated.
A shallow chamber through which molten glass passes on its way from
a continuous melting furnace to the forming process. The purpose of this
chamber is to allow the temperature of the glass to drop from melting
temperatures (about 2,700°F) to forming temperatures (about
2,200°F for 1/8" thick sheet glass).
(See Process Diagram.)
An enclosed chamber through which formed glass products are
carried for the purpose of annealing.
- Pot Furnace
A melting chamber in which one or more ceramic pots are placed.
Batch is fed into the individual pots through ports in the chamber walls,
and when melted, glass is ladled from the pots via the same ports.
Each pot is fairly small. The pot furnace allows the melting of a
number of different glass colors (as many as there are pots) at
the same time, within a single melting chamber.
Glass Sheet Forming Methods
Sheet glass types are often by delineated by how the sheet is
formed. Thus, people speak of "mouth-blown," "double-rolled,"
"drawn glass," "float glass," "hand cast glass," and so on.
- Blown Cylinder Method
See Full Antique
- Single Roll Method
Molten glass is poured onto a metal table and a single metal
roll is used to flatten it into a sheet. Sometimes called "hand cast" sheet glass.
- Double Roll Method
Molten glass is passed between a pair of rotating metal rolls
to form the sheet.
- Vertical Draw Method
Molten glass is pulled up vertically through a slit in a large
one-piece refractory block that is floating on the glass surface.
The annealing lehr is mounted vertically over the draw chamber.
Drawn glass is generally more pristine than rolled glass
because its surface has remained untouched during forming.
- Float Process
Molten glass is pulled from the forehearth atop a bath
of molten tin. The process produces a perfectly smooth sheet
of uniform thickness in high volume. The float process is used
to produce virtually all common window glass today, thus the
term "float glass." Not used for art glass production.