Glass Art Glossary Terms
For non-designers, glass lexicon can be challenging. Glass
collectors and decorators
struggling
to find the right words to describe a glass product or look will
want to bookmark this page for easy reference.
Acid Etching - This process for the decoration of glass involves the
application of hydrofluoric acid to the glass surface. Hydrofluoric acid
vapors or baths of hydrofluoric acid salts may be used to give glass a
matte, frosted appearance (similar to that obtained by surface
sandblasting), as found in lighting glass. Coating the glass with wax and
then inscribing the desired pattern through the wax layer can produce
glass designs. When applied, the acid will corrode the glass but not
attack the wax-covered areas.
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.
Annealing - The process of slowly cooking a completed object in the
furnace. The furnace is called an annealer or a Lehr. This is an integral
part of glassmaking because the glass will be highly strained if it
reaches room temperature too quickly and may break.
Antique Glass - Glass with an uneven surface texture and bubbles inside
produced using antique methods in order to obtain the appearance of glass
made before the development of industrial processes. It may be drawn or
produced from mouth-blown cylinders.
Art Glass - (1) Several types of glass with newly developed surface
textures, shaded color, or casting, made in the United States from about
1870 and in Europe between about 1880-1900; (2) more generally, any
ornamental glasswork made since the mid-19th century.
At-The-Fire - The process of reheating a blown glass object at the glory
hole during manufacture, to permit further inflation and/or manipulation
with tools.
Batch - The mixed raw materials used in manufacturing glass that have been
blended and proportionally mixed for delivery to the glass furnace.
Bending - A process whereby the shaped glass article still in sheet form
is placed on a stainless steel, sheet steel or cast iron mold coated with
talc or powdered chalk. The temperature is increased until the glass sheet
sinks in to the mold.
Bits - Pieces of molten glass snipped off a blowpipe or punty rod and
applied hot to a glass form.
Blank Mold - The metal mold in which the parison is formed.
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.
Blanks - The mold parts used in all glass container machines for
preliminary formation of glass in preparation for the most efficient
completion of glass containers in the finish molds where bottles are
blown. The blank forms the parison. The parison itself is at times
referred to as the blank.
Blister - A gaseous inclusion or bubble in the glass.
Blobbing - The technique of decorating hot glass by dropping onto the
surface blobs of molten glass, usually of a different color or colors.
Block - A block of wood hollowed out to form a hemispherical recess. After
it has been dipped in water to reduce charring and to create a "cushion"
of steam, the block is used to form the gather into a sphere, prior to
inflation.
Blowing - The technique of forming an object by inflating a glob of molten
glass gathered on the end of the blowpipe. The gaffer blows through the
tube, slightly inflating the glob, which is then manipulated into the
required form by swinging it, rolling it on a marver, or shaping it with
tools or in a mold; it is then inflated to the desired size.
Borosilicate Glass - A high silicate glass with at least 5% boron oxide.
Bubbles - A pocket of gas trapped in glass during manufacture. The term is
used for both bubbles introduced intentionally (also known air traps or
beads) and bubbles trapped accidentally during the melting process. Very
small bubbles are known as seeds.
Bullions - One of the few forms of flat glass still produced by the hand
process. Bullions or "bull' eyes" are used for decorative window glass and
are made by reheating and spinning out a bowl-shaped piece of glass.
Cable - A pattern resembling the twisted strands of a rope.
Came - A grove strip of lead or (rarely) another metal, generally with an
H shaped cross section, used to join separate parts of glass window.
Cane - A thin, monochrome rod, or a composite rod consisting of groups of
rods of different colors, which are bundled together and fused to form a
polychrome design that is visible when seen in cross section.
Caning - The removal of glass from the surface of an object by means of
handheld tools.
Casing - The application of a layer of glass over a layer of contrasting
color. The gaffer either gathers one layer over another gather, or
inflates a gob of hot glass inside a preformed blank of another color. The
two components adhere and are inflated together (perhaps with frequent
reheating) until they have the desired formed.
Cast Glass - Glass produced by "casting', in other words by pouring molten
glass into a mold or by heating glass already contained in the mold until
the glass melts and assumes the shape of the mold.
Casting - The generic term for a wide variety of techniques used to form
glass in a mold.
Cerium Oxide - The oxide of the rare earth, cerium, used alone or together
with other substances as a polishing agent for glass.
Cobalt - A silvery-white magnetic metallic element, which, even in small
quantities, gives a strong blue coloration to glass. It can be used as a decolorizor on its own for opal glasses. For flint, it may be used with
selenium, manganese, nickel or cerium.
Cold Working - The collective term for the many techniques (such as
engraving or cutting) used to alter or decorate glass when it is cold.
Used to create texture or pattern into the surface.
Copper-Wheel Engraver - A technique of decorating the surface of an
object. Copper disks (wheels) of various sizes and rim profiles are
rotated on a spindle. An abrasive such as Carborundum, mixed with oil, is
applied to the edge of the wheel. The wheel presses the abrasive against
the glass so that it removes the surface by grinding.
Cords - Flaws in the material, which affects the artist's ability to work
with the glass.
Core Forming - The technique of forming a vessel by trailing or gathering
molten glass around a core supported by a rod. After forming, the object
is removed from the rod and annealed. After annealing, the core is removed
by scraping.
Core - The form to which molten glass is applied in order to make a core
formed vessel.
Cracking Off - The process of detaching a glass object from a blowpipe or punty.
Crackle Glass - To produce the crackle effect, the parison is rolled in
moist sawdust or covered with sand in order to give the surface a coarse
finished. It is then submerged in water, causing the surface to crack,
without destroying the glass. A fresh layer of glass is then added and
reheated until the cracks fuse together slightly so that the glass
maintains its stability.
Crown glass - Window glass blown into a crown or hollow globe that is
flattened and cut before use. This is produced by reheating and spinning
out a bow-shaped piece of glass (bullion) that causes the glass to extend
into a flat disk by centrifugal force. The glass is then cut into the size
required.
Dalle Glass - Colored glass produced in pot furnace and cast in molds to
form plates. Dalle glass ("dalle" is French for "tile") is used in church
and decorative glazing, as well as for furnishing such as door handles.
Dichroic - A type of manufacturing glass which has ability in two
different ways. Color is transmitted through the glass and complimentary
colors are reflected from the surface.
Electroplate - A process by which metal is adhered to glass by dipping it
into an electrically charged solution. Encased Painting on Glass: The
process of painting a glass object with glass paint, then subsequently
re-heating the glass and gathering more hot glass over the surface,
encasing the paint in glass.
Enamel - A vitreous substance made of finely powdered glass colored with
metallic oxide and suspended in an oily medium for ease of application
with a brush. The medium burns away during firing in a low-temperature
(muffin) kiln (about 500-700 degrees Fahrenheit). Sometimes, several rings
are required to fuse the different colors of an elaborately enameled
object.
Engraved - The process of cutting into the surface of an annealed glass
object either by holding it against a rotating copper wheel fed with an
abrasive or by scratching it, usually with a diamond.
Engraving - The production of a design in glass by cutting into the glass
surface. Engraving methods include copper wheel engraving, diamond, of
tungsten point engraving, acid etching and sand blasting.
Etch - To create a design by cutting the surface of finished glass with a
tool or treating it with acid.
Figured Glass - Also known as "patterned" or "ornamental" glass, figured
glass is generally produced by the rolling process. The surfaces of the
rollers used carry the pattern or design to be "imprinted" in the glass as
it passes between them. The process gives the glass a texture surface on
one side or both sides. The surface finish may be both decorative and
functional. Apart from the huge variety of patterns possible, figured
glass can also offer light dispersion and glare reduction characteristics.
Filigrana - The generic name for blown glass made with colorless, white,
and sometimes colored cane. The filigrana style originated at Murano,
Italy in the 16th century and spread through Europe.
Finished - The process of completing the forming or decorating of an
object. Finishing may take the form of manipulating the object into its
final shape while it is hot, of cracking off prior to annealing, or of
grinding, cutting or polishing.
Fire-Resisting Glass - Flat glass with a wire inlay which helps retard
shattering in the event of fire and thus delays the spread of smoke and
flames. Such glazing is classified either as class G (which resists fire
and prevents the spread of smoke and flames for a specific period of time)
or class F (which has the characteristics of class G but also impedes the
spreading of radiant heat for specific periods). New developments include
pre-stressed wire-free borosilicate glass and double-glazing with the
inner space filled with an intumescent material which acts as a heat
shield
Firing - The process of bringing a glass furnace up to its operational
temperature and then maintaining the temperature.
Flameworking - The technique of forming objects from rods and tubes of
glass that, when heated in a flame (gas-fueled torches), become soft and
can be manipulated into the desired shape.
Flashing - The application of a very thin layer of contrasting color. This
is achieved by dipping a gather of hot glass into a crucible containing
hot glass of the second color.
Flat Glass - AII types of glass (rolled, float, plate, etc.) produced in a
flat form, regardless of the method of production. Float process: A method
for the production of high-quality sheet glass whereby a ribbon of molten
is fed across a bath of heated liquid, usually molten tin, in a carefully
controlled atmosphere. The UK firm Pilkington Brothers developed the
process.
Flint - A glass color or lack of color. Flint is perfectly clear
transparent glass, like window glass, used for all types of containers.
Founding - The initial phase of melting batch. The material must be heated
to a temperature of about 2450 degrees Fahrenheit. This is followed by a
maturing period, during which the molten glass cools to a working
temperature of about 2000 degrees Fahrenheit.
Frit - Batch material that is melted with other materials and then ground
into powder form before being added to the batch. Lead oxide, which can
produce a harmful dust, may be melted with silica, for example, and then
ground down as a lead silicate.
Fusing - (1) The process of rounding or melting the batch; (2) healing
pieces of glass in a kiln or furnace until they bond; (3) heating enameled
glasses until the enamel bonds with the surface of the object. Fusing
glass-to-glass: Glasses of different compositions can be fused together
for decorative purposes and also in the sealing of electric, medical and
industrial components. The fusion temperature for soda-Iime glasses is
generally between 760 and 820C. Particular attention must be paid to the
thermal expansion coefficients of different glass types.
Gaffer - The master craftsman is charge of the team of hot workers.
Gather - (Noun) A mass if molten glass collected on the end of a blowpipe
or punty. (Verb) to collect molten glass on the end of a tool.
Gathering Iron - A long, thin tool used to gather molten glass.
Glass - A homogeneous material with a random, liquid like molecular
structure. The manufacturing process requires that the raw materials be
heated to a temperature sufficient to produce a completely fused melt,
which, when cooled rapidly, becomes rigid without crystallizing.
Glory Hole - A hole in the side of a glass furnace, used when reheating
glass that is being fashioned or decorated. The glory hole is also used to
fire-polish cast glass to remove imperfections remaining from the mold.
Glassblowing -The shaping of glass using air pressure.
Grall - A glassblowing technique wherein a thick "blank" or core form is
blown, usually with two or more layers of color. The blank is then
engraved, bringing out the underlying color much like a cameo. The
engraved blank is subsequently reheated and blown to full shape, fusing
the image into the surface.
Grinding - The removal of glass with abrasive or abrasive (grinding)
wheels in order to shape, polish or otherwise finish both flat and hollow
glass. Grinding process include milling, sawing, edging, and drilling.
Hard Glass - A glass with a high softening point or high viscosity
(usually borosilicate).
Hydrofluoric Acid - A highly corrosive acid that attacks silicates such as
glass. Purehydrofluoric acid dissolves glass, leaving a brilliant,
acid-polished surface.
Incalmo - The process in glassblowing of joining two or more bubbles of
hot glass together to create defined bands of color.
Intaglio - A method of engraving whereby the orientation is cut into the
object and lies below the surface plane.
Kiln Cast - The use of a mold, usually plaster, filled with crushed glass,
which is melted in a kiln to produce a solid glass form.
Kiln - A high-temperature electric oven, usually monitored by a computer,
used for casting, fusing and slumping glass.
Laminated Glass - Laminated (or compound) glass consists of two or more
sheets of glass with one or more viscous plastic layers "sandwiched"
between the glass panes. The solid joining of the glass takes place in a
pressurized vessel called an autoclave. In the autoclave, under
simultaneous heating of the already processed layers of glass and special
plastic, lamination occurs. When laminated safety glass breaks, the pieces
remain attached to the internal plastic layer and the glass remains
transparent.
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).
Lost Wax Casting - The object to be fashioned in glass is melded in wax
and encased in clay or plaster that is heated. The wax melts or is "lost"
, leaving a mold into which hot glass can then be poured. The mold must be
broken in order to retrieve the cast object.
Marver - A smooth, flat surface, over which softened glass is rolled in
order to smooth it or to consolidate applied decoration.
Melt - The fluid glass produced by melting a batch of raw materials.
Millefiori - Objects made from preformed elements placed in a mold and
heated until they fuse. Millefiori is a Venetian term. The term "mosaic
glass" is also accepted. Mold: A form normally made of wood or metal.
Mold-Blown - Glass formed into a shape by being blown into a mold usually
made of wood, metal or plaster.
Mosaic Glass - Produced by a glassblower rolling the hot glass globe over
a marble or iron plate covered with small pieces of colored glass. These
pieces adhere to the surface of the globe. The object is then overlaid
with clear glass before being finished.
Murrinni - Patterned glass cane cut into sections to form small disks used
in decorating glass or constructing glass.
Off-Hand - Formed free hand on the end of a punty of blowpipe. No mold is
used.
Optical Glass - The glass in lenses and prisms, in which homogeneity,
refractive characteristics and the absence of defects such as seeds area
of major importance. In many modern optical glasses, lead oxide has been
replaced with barium oxide while lanthanum oxide is used for optical glass
with low dispersion and a high refractive index.
Overlay - A thin layer of clear or colored glass on the outside of a
piece.
Opal Glass - Glass that resembles an opal, being translucent and white,
with a grayish or bluish tint.
Paradise Paint - A specially formulated glass paint, which will not loose
color when, exposed to the intense heat of molten glass. Paradise paint is
often used to decorate pieces created using encased painting or graal
techniques. Patterned glass: see figure glass.
Pick-up Decoration - A technique whereby a hot parison is rolled in chips
of glass, which are picked up, marvered, and inflated.
Plate Glass - Flat glass made by the casting or rolling of molten glass
which is then mechanically ground and polished to produce a smooth and
transparent sheet.
Pipe – A long hollow steel rod used in glass blowing. By blowing through
the pipe, the glass is formed into the preliminary shape. Sometimes
referred to as a “rod”.
Polishing Wheel - Traditionally made of wood or bristle and more recently
of cork, polyurethane and bonded cloth, these discs are used in
conjunction with abrasive pastes to polish glass surfaces. Felt wheels
with material such as cerium oxide and other commercially produced powders
are now widely used for fine polishing. In the polishing process, the
wheel is rotated at speed by means of a motor and applied to the glass to
be polished.
Polishing - Smoothing the surface of an object when it is cold by holding
it against a rotating wheel fed with a fine abrasive. Glass can also be
polished with hand-held tools.
Pontil - The pontil, or punty, is a solid metal rod that is usually tipped
with a wad of hot glass, and then applied to the base of a vessel to hold
it during manufacture. This is called the "punty mark".
Pot - A fire clay container placed in the furnace in which the batch of
glass, raw materials used to make glass, is held and melted. The glass
worker gathers directly from the pot.
Punty – A solid metal rod that is usually tipped with a wad of hot glass,
and then applied to the base of a vessel to hold it during manufacture.
This is called the "punty mark".
Reticello - {Vetro a Reticello) A type of blown glass made with canes laid
in a crisscross pattern for form a net.
Sand - The most common form of silica used in making glass.
Sandblasting - To blow or blast sand or Carborundum onto a piece of glass,
which etches or blasts away layers of glass. Masking is used to create
patters.
Sandblown - The process of blowing a bubble of hot glass into sand mold.
Sandcast - To ladle hot glass into a mold made of special casing sand.
Sar - A single piece of glass formed by fusing several canes or rods. A
bar can be cut into slices, all with the same design, to be used as inlays
or appliqués, or making mosaic glass.
Satch - The mixture of raw material (often silica, soda or potash, and
lime) that is melted in a pot or tank to make glass. Gullet is added to
help the melting process.
Scavo - Corrosive chemical material added to the surface of hot glass,
which gives a matte finish to the final piece.
Screen-Printing - A process for the decoration of glass whereby colored
ink is forced by a flexible "squeegee" through a fine-mesh screen, or
"mask", {traditionally made of silk, now also made of nylon, polyester and
stainless steel) onto the glass surface. A separate mask is used for the
application of each color. Considerable automation of the process has been
developed, thus allowing extremely high printing speeds for even complex
designs.
Scruffitto - Color is added to the surface of glass and then scratched
away, so that an image appears in reverse.
Seeds - Minute bubbles of gas, usually occurring in groups.
Shard - A small fragment of glass. Colored shards can be melted into
pieces for decoration.
Slump - To heat a sheet of glass in a mold until it is soft enough to
assume the mold shape with out becoming molten.
Smalti - A soft, intensely colored Venetian glass that is chipped into
squares for use in creating traditional mosaic.
Soda-Lime (or Soft) Glass - A glass with a substantial portion of lime in
the formula.
Softening Point - The specific temperature in which glass is just barely
able to maintain its shape and not flow like a liquid.
Softening Point - Temperature at which a thread or rod of glass rapidly
deforms under its own weight.
Stippling - (1) The technique of tapping the surface of a glass objects
with a pointed tool, often a diamond or tungsten carbide tip. Each tap
produces a mark, and the decoration is composed of many hundreds and
thousands of marks. (2) On lacy-pattern pressed glass, the stippling is
part of the decoration of the mold.
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.
Studio Glass Movement - A movement that began in the United States in the
1960's and has spread allover the world. It is characterized by the
proliferation of glass artist who are not affiliated with factories, but
work with hot glass in their own studios. The emergence of independent
glass artists was made possible by Harvey Littleton and Dominick Labino's
developments in 1962 of a small furnace and easy-to-melt glass.
Threads - Thin strands of glass usually colored, which can be added to the
glass in a variety of ways for different effects.
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.
Trail - A strand of glass, roughly circular in section, drawn out from a
gather.
Undercutting - The technique of decorating glass in high relief by cutting
away part of the glass between the body of an object and its decoration.
Type I Glass - Containers made of Type I 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.
Underlay - A thin layer of clear of colored glass on the inside of a
piece. Weathering: Changes on the surface of glass caused by chemical
reaction with the environment. Weathering usually involves the leaching of
alkali form glass by water, leaving behind siliceous weathering products
that are often laminar.
Weathering - The attack on glass surface by atmospheric elements.
Wheel Engraver - Wheel engraving process of decorating the surface of
glass by the grinding action of a wheel, using disks or various size and
materials (usually copper but sometimes stone). An abrasive in a grease or
slurry is applied to a wheel, as the engraver holds the object against the
underside of the rotating wheel.
Wrap - A strand of glass applied hot to a vessel.
Zanfirico - The process of heating up cut canes of glass (usually with an
Interior spiral pattern) and gathering them onto a pipe to be blown into
shape. Also know as filigrana. Formerly called latticino.
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