Glossary of Glass
and Pottery Terms
Glassmaking terms
Acid-etching
Etching glass by applying hydrofluoric acid (neat, or in a diluted
paste form - depending on the effect required) over an incised
shellac or wax "resist"
Acid-polishing
Modern (widely used since c 1880s, although originally patented in
1857 by W H, B & J Richardson) quick method of "polishing" cut
glass by dipping in a mixture of hydrofluoric and sulphuric acid.
Cheaper than mechanical polishing, but tends to "round off" cuts,
thus losing definition
Annealing
Process by which a hot glass item is (after completion) uniformly
re-heated and then gradually cooled down over many hours in the
Lehr, in order to toughen it and make it less likely to crack when
subjected to changes of temperature
Applied decoration
Hot glass added to a blown article, usually flowers, fruit, leaves
or trailing
Art glass
Decorative glass, which may or may not have a function, but which
is essentially individually hand-blown, often as one-off or
limited edition pieces. Sometimes referred to as Studio glass
Aventurine
Inclusion of a suspension of copper particles, as in the man-made
gemstone of the same name
Blank
A
plain glass object, usually hand-blown, intended for cutting,
engraving, enameling or gilding by a refiner. May also be cased
Blow-pipe
Hollow iron pipe onto which a gather of metal is placed and blown
Bullicante
Containing a regular, controlled pattern of bubbles
Cameo
Similar to Hochschnitt, but using two or more layers of cased
glass in different colours, the outer layer(s) being cut away to
leave a design in relief (often flowers)
Cane
Rod of multicoloured glass, made up of smaller individual rods
fused together, then stretched
Cased
Two or more substantial layers of different coloured glass blown
over one another (one or more layers of which may be cut away to
reveal the layer(s) beneath)
Casting
Ladling hot glass into a mould (often created by the Cire perdu
process) and allowing to solidify before annealing
Cold-enamelling
Enamels painted on to cold glass, but not fired (a cheap process,
but the enamel is liable to wear off in time)
Copper-wheel
Engraving using foot- or machine-powered small copper wheels
coated with abrasive pastes
Cut glass
Glass blanks, hand-cut on large iron or stone grinding-wheels and
then polished
Dab handle
The modern style of handle, where the glass is applied first to
the bottom anchor-point, then pulled upward and attached at the
top.
Diamond-cut
Method of cutting in parallel diagonal V-shaped grooves in two
opposing directions, so as to leave faceted lozenge-shapes. Also
imitated in pressed glass
Diamond-point
A
method of hand-engraving by scratching or stipple-engraving glass
with a diamond-pointed tool
Dip-mould
One-piece mould into which the gather is dipped before blowing, to
give a particular surface effect such as a pattern of parallel or
diamond-ribbing
Enamels
Variously-coloured opaque or transparent pigments composed of
glass powder, metallic oxides and a flux (e.g. borax). As in
pottery glazes, the final colour was often not apparent until
after firing
Enamelling
Process of painting enamels on to cold glass, then firing in a
low-temperature kiln so that they fuse into the surface and are
relatively resistant to wear
End-of-day glass
Produced (often by apprentices) by rolling a gather onto a random
assortment of coloured glass fragments (literally, whatever was
left at the end of the day) on the marver, then blowing and
shaping (compare Spatter glass)
Etching
Decorating the surface of usually thin glass articles by means of
scratching with a diamond-point or treating with acid.
Facet-cut
Cut in the fashion of gemstones, with adjoining flat planes
Filigrana
Filigree, a general term used to describe embedded threads or
ribbons of coloured glass, either in parallel or network patterns
Firing glass
Short, rudimentary-stemmed, funnel- or trumpet-bowled glass on a
thick foot, used on ceremonial occasions when, after a toast, the
glasses would be rapped on the table like a volley of shots being
fired.
Flashed
Usually clear glass dipped in a thin film of coloured glass and
often engraved
Flint glass
Original, but not strictly correct, name for English Lead glass
Fluting
Cut or moulded relief ornamentation of a series of narrow or broad
parallel concave flutes.
Folded foot
The rim of the foot is folded back under to give added protection
against chipping
Foot
The base of a glass. Until the invention of the gadget, was held
by the pontil-rod while the glass was being finished. After c 1800
the pontil-mark was usually ground out, so the foot could be made
flat.
Free-blown
Another term for hand-blown.
Frigger
Usually small glass article made by craftsman outside normal
working hours, as a gift or for sale, or lampworked article by an
itinerant glassblower. Often of no functional use. Known as a
"whimsy" in the USA
Frosted glass
Glass given a semi-opaque frosted surface by dipping in, or
exposing to the fumes of, a mixture of hydrofluoric acid and
ammonia
Gadget
Spring-clip device used (from c 1860) for holding the foot of a
drinking-glass while it was finished, so obviating the pontil mark
Gadget mark
Faint mark in the shape of a Y or T, left by the gadget. After c
1900, asbestos pads prevented this mark appearing
Gadroon
Ornamental decoration of continuous reeding, either vertically,
horizontally or twisted. First used on 17th century silverware
Gather
An
amount of hot metal appropriate to the size of the article being
blown or pressed, gathered onto the blow-pipe before blowing
commences
Gilding
Ground gold-leaf mixed with oil, honey or mercury, painted on then
fired in a low temperature kiln
Graffito
A
technique whereby gold leaf is applied to the surface of an
article, and then scraped away in places with a pointed implement,
to leave a pattern
Hand-blown
The article is blown and manipulated entirely by hand
Hobnail-cut
Method of cutting parallel horizontal and diagonal in opposing
directions, V-shaped grooves, so as to leave faceted hexagonal
hobnails. Also imitated in pressed glass
Hochschnitt
High-relief cutting (as in Cameo glass) where the background is
cut away to leave raised decoration.
Hydrofluoric acid
The only acid that will dissolve glass. Neat, it leaves a clear
finish; in conjunction with sulphuric acid, it produces a high
gloss finish used in polishing lead glass; in mixture with
ammonia, it produces frosting
Incalmo
A
technique whereby two bubbles are blown, then cut and fused along
their rims before final shaping. Possibly refers to the calmness
required to perform this tricky operation
Incised-twist
Cheaper imitation of air-twist stem, with external parallel
grooving twisted to give a spiral pattern
Inclusions
Any metallic particles, foil, bubbles, sections of millefiori
cane, pieces of contrasting-coloured glass or any other bodies
embedded in the main body of the glass
Intaglio
Engraving using small stone wheels to create mostly curved cuts
(such as flowers or leaves), giving the visual illusion that the
cut-away parts are actually raised (also called Tiefschnitt)
Knop
Decorative feature of the stem, formed by re-heating part of the
stem and compressing it, or made separately and inserted into the
stem (as with Venetian-style glasses).
Lacy glass
A
type of mainly American and French pressed glass with elaborate
moulded decoration, any gaps being filled with small raised dots,
thus hiding many of the faults inherent in early pressed glass.
First developed c 1830 by Deming Jarves of Boston & Sandwich Glass
Co (also called Sandwich glass)
Lampwork
Articles formed out of thin rods or canes over a small burner,
usually small ornaments (also miniature flowers, insects etc for
inclusion in paperweights)
Latticino
Lattice, fine threads of specifically lattimo glass in spiral or
net patterns
Lattimo
Opaque white glass (from latte, the Italian for milk)
Lead crystal
Glass containing a high proportion (about 25 to 30%) of Lead Oxide
Lead glass
Discovered by George Ravenscroft in 1673. Often (not strictly
correctly) called Flint glass, it contains Lead Oxide, as opposed
to Potash glass or Soda glass. It cools rapidly, making it hard to
manipulate into complex shapes, but its hardness and brilliance
make it well-suited to cutting and engraving
Lehr
Oven used for annealing.
Machine-threaded
Thread of (often coloured) glass mechanically wound on to a
hand-blown article
Marver
Flat metal plate onto which the article being blown may be pressed
or rolled when being shaped. Sometimes deliberately covered with
fragments of broken glass or pieces of cane which then fuse to the
exterior of the article
Mercury twist
A
rare form of air twist stem where the air bubbles are flattened,
the increased reflective surface giving a quicksilver effect
Merletto
Various different net-like patterns of lattimo threads
Metal
The basic glass mixture, particularly when molten
Mezza filigrana
Half-filigree, a pattern of fine parallel (often diagonal or
spiralled) threads, ribbons or rods
Mica flakes
Used as an inclusion, reflects light somewhat like silver-leaf
Millefiori
Literally, "thousand flowers". A type of Murrine consisting of a
slice of a flower-shaped multicoloured cane, either fused together
with others, picked up from the marver, or embedded in clear
glass.
Mixed twist
A
rare mixture of opaque and air twists within a stem. Rarest of all
include air, opaque and colour twists
Mosaic glass
Sections of murrine fused together flat, then either (a)
joined into a cylinder before being manipulated or blown into the
final shape, or (b) slumped over a former to create the required
shape
Mould-blown
The paraison is blown into a mould, either by hand or as part of a
mechanised process
Murrine
Short lengths or slices of canes (including millefiori), used in
mosaic glass, or picked up onto the gather or paraison from the
marver before or during blowing, and therefore sometimes smeared
or distorted in the finished article (also spelt Murrhine)
Opaque twist
Type of stem, also known as "cotton" twist, popular c 1755-1780,
drawn from Venetian latticino techniques, where threads of lattimo
are enclosed in clear glass and twisted to produce elaborate
spirals
Overlay
Another term for cased glass
Panel-cut
Cut in broad flat panels
Paraison
The gather of molten metal on the end of the blow-pipe, when
partially inflated into a bubble
Pâte de verre
French for glass paste. Powdered coloured glass and a flux, put
into a mould and then fired to fuse it, giving a translucent
effect like alabaster. Sometimes several layers, then cut back.
Invented in ancient Egypt, revived in France late 19th Century
Pillar-cutting
Cut or moulded relief ornamentation (also called reeding) of a
series of parallel, vertical convex reeds
Plique-ŕ-jour
A
delicate process, whereby transparent enamel powders are
introduced into a soldered metal framework over a removable core,
then fired, giving the effect of stained glass. Much used in Art
Nouveau jewellery, more rarely for other items
Polishing
Originally by rotating cork wheels or brushes, using progressively
finer abrasive pastes and powders (see also Acid-polishing)
Pontil mark
Rough mark left where article was attached to pontil rod before
being allowed to cool and broken off. From c 1800 -1860 usually
ground and polished out (from c 1775 in facet-stemmed glasses)
Pontil rod
Also known as the punty rod, the solid iron rod onto which a blown
article is transferred from the blow-pipe for final shaping and
finishing
Potash glass
Sometimes called fern-glass or forest-glass, contains Potassium
Carbonate. It is heavier than Soda glass, and solidifies more
quickly, making it less easy to manipulate, but its increased
hardness makes it more suitable for cutting and engraving
Pressed glass
Gather pressed by a metal plunger into a mould, either by hand or
as part of a mechanised process
Printies
Small round or oval ground-out depressions as decoration (possibly
corruption of punty)
Prunt
An
applied roundel of glass added to decorate a blown item, often in
the form of raspberries or lion's heads
Pulegoso
Bubbled, containing a froth of random-sized bubbles
Pump handle
An
early style of handle, where the glass is applied first at the
top, then pulled down and attached at the bottom. Continued
briefly after the introduction of the dab handle, then fell
into disuse
Punty
Alternative term for pontil
Refiner
One who decorates bought-in glass blanks by cutting, engraving,
gilding, enamelling etc.
Reeding
Cut or moulded relief ornamentation (also called ribbing when
moulded) of a series of parallel convex reeds (as opposed to
flutes, which are concave)
Resist
An
acid-resistant coat of shellac or beeswax, cut-out or scratched
wherever the effect of the acid is required
Rock crystal
Naturally-occurring Quartz. Also a style of engraving glass where
all the engraved parts are polished, giving a more brilliant
effect.
Sand-blasting
A
coarse method of etching glass by firing abrasive powders through
a stencil
Scavo
Literally "excavated". A technique whereby sand is applied to the
finished article, to give the effect of ancient glass which has
lain buried for centuries
Schmelze
The more-or-less random application of threads and pieces of
coloured glass to the surface of a piece, which are then re-heated
and marvered flat
Seed
A
small piece of waste material that has been accidentally picked up
in the gather, and more commonly found in the glassware of the
18th Century or before
Silver leaf
Genuine silver leaf used as an inclusion
Slumping
Method of shaping glass by heating in a furnace until it melts
enough to sag over a former
Soda glass
Contains Sodium Carbonate. It remains plastic after heating for
longer than either Potash glass or Lead glass, and can therefore
be worked into the more intricate forms such as those favoured by
Venetian glassmakers
Sommerso
Literally "submerged". Small pieces or larger glass shapes heavily
cased in another colour
Spatter glass
Also called Cottage glass. Produced by rolling a (often opaque
white) gather of glass onto a deliberately-arranged selection of
coloured glass fragments on the marver, then re-heating, blowing,
casing in clear crystal and shaping (compare End-of-day
glass)
Staining
Method of colouring glass by brush-applied stain (amber or ruby)
invented in Bohemia, and used in last half of 19th Century as
cheap substitute for flashing. Usually fired at low temperature,
then engraved
Stipple-engraving
Using a diamond-pointed tool as a chisel, to chip away minute
fragments of glass
Stem
The part of a drinking-glass joining the bowl to the foot. May be
plain, knopped, and/or decorated internally or externally.
Teardrop
A
bubble of air, usually resembling a teardrop, as decoration within
the stem or knop
Tiefschnitt
Intaglio cutting (the opposite of Hochschnitt), where the body of
glass is cut away in low-relief, but giving an optical illusion of
raised decoration
Trail
Thread of (often coloured) glass applied by hand to a hand-blown
article
Uranium glass
Yellow glass, coloured with a small amount of uranium, which
fluoresces under ultra-violet light.
Vetro a fili
Clear article with embedded threads in spiral pattern
Vetro a reticello
Clear article with embedded criss-crossed threads forming regular
networks, usually with tiny air-bubbles between the crossed
threads
Vetro a retorti
Clear article with embedded twisted threads forming lace-like
patterns
Whimsy
Usually small glass article made by craftsman outside normal
working hours, as a gift or for sale, or lampworked article by an
itinerant glassblower. Often of no functional use.
Wrythen
Simple decoration where external parallel grooves or ribs (applied
either by hand or by blowing the paraison into a dip-mould) are
given a twist during blowing to create a spiral pattern
Pottery making terms
Bagwall
The wall on the inside of a fuel
burning kiln which deflects the flame from the wear.
Bat
A flat disc made out of plaster,
wood, or plastic which is affixed to the wheel head with clay or
pins.
Bats are used to throw pieces on
that would be difficult to lift off the wheel head.
Batch
A mixture of weighed materials such
as a batch of glaze or slip or a clay body.
Banding Wheel
A revolving wheelhead which sits on
a pedestal base. It is turned by hand and used for finishing
or decorating pottery.
Bisque
Pottery which has been fired once,
without glaze, to a temperature just before vitrification.
Bisque Fire
First firing, without glaze. Slips
can be used in a bisque firing.
Bone Dry
Completely air dried.
Burnishing
The ancient rubbing process of
burnishing polishes the outside skin of a clay pot while
greatly reducing its porosity. This
finishing is done by hand, using a stone or a metal
piece which is usually embedded in a
wad of wet clay that perfectly fits the burnisher's hand.
Calipers
A tool used to measure the diameter
of round forms, for example calipers are used to get lids
to fit just right.
Centering
Technique to move the clay in to a
symmetrical rotating axis in the middle of a wheel head
so you can throw it.
Chuck
A piece used to aid the potter in
trimming. A chuck is a form that can hold a pot upside-down
above the wheel head while the
potter trims it. Chucks are thrown and bisque fired clay cylinders
which are open on both sides.
Clay
Alumina + silica + water.
Clay body
A mixture of different types of
clays and minerals for a specific ceramic purpose.
For example, Porcelain is a
translucent white clay body.
Coil
A piece of clay rolled like a rope,
used in making pottery.
Compress
Pushing the clay down and together,
forcing the particles of clay closer.
Composite Pots
Pots that were thrown or hand built
in separate pieces and then assembled.
Cone
Pyrometric - A pyramid composed of
clay and glaze, made to melt and bend at specific temperatures. It
is used in a kiln to determine the end of a firing or in some
electric kilns it shuts off a kiln setter.
Crazing
The cracking of a glaze on a fired
pot. It is the result of the glaze shrinking more than the clay
body in cooling process.
Crawling
A bare spot (from the shrinking of a
glaze) on a finished piece where oil or grease prevents the glaze
from adhering to pottery.
Damper
A slab of refractory clay that is
used to close or partially close the flue of a kiln.
Dry-Foot
To keep the foot or bottom of a pot
free from glaze by waxing or removing the glaze.
Earthenware
A low fired clay body. Glazed
pottery is fired to a temperature of 1,830 - 2,010 degrees
Fahrenheit. Available in red or also white.
Englobe
Colored clay slip used to decorate
Greenwear or leather hard pieces before bisque firing. Clay and
oxide and water.
Fire
To heat a clay object in a kiln to a
specific temperature.
Firebrick - An insulation brick used
to hold the heat in the kiln and withstand high temperatures.
Firing Range
The range of temperature at which a
clay becomes mature or a glaze melts.
Flux
A melting agent causing silica
to change into a glaze.
Foot - Base of a ceramic form. Frit
- A glaze material which is derived from flux and silica which are
melted together and reground into a fine powder.
Glaze
A thin coating of glass. An
impervious silicate coating, which is developed in clay ware by
the fusion under heat of inorganic materials.
Glaze firing
The final firing, with glaze.
Gloss Glaze
A shiny reflective gloss.
Greenware
Unfired pottery. Ready to be bisque
fired.
Grog
Fired clay ground to various mesh
sizes.
Kiln
A furnace of refractory clay bricks
for firing pottery and for fusing glass.
Kiln Furniture
Refractory posts and shelves used
for stacking pottery in the kiln for firing.
Kiln Wash
Mixture of Kaolin, flint and water..
It is painted on one side of the kiln shelves to separate any
glaze drips from the shelf.
Leather Hard
Stage of the clay between plastic
and bone dry. Clay is still damp enough to join it to other pieces
using slip. For example, this is the stage handles are applied to
mugs.
Majolica
A low fire glazing technique. The
process involves applying an opaque tin glaze to earthenware and
painting it with different colored oxides.
Matt Glaze
A dull glaze surface, not very
reflective when fired. It needs a slow cooling period or it may
turn shiny. Mold - A plaster shape designed to pour slip cast into
and let dry so the shape comes out as an exact replica of the
mold.
Maturing Point
The temperature at which the clay
becomes hard and durable.
Opaque Glaze
Non-transparent glaze, it covers the
clay or glaze below it.
Oxidation
Firing with a full supply of oxygen.
Electric kilns fire in oxidation. Oxides show bright colors.
Peephole
A small observation hole in the wall
or door of a kiln.
Pinch
Manipulate clay with you fingers in
your palm to a hollow shape. Pinch pots are a popular beginners
project.
Plasticity
The quality of clay which allows it
to be manipulated into different shapes without cracking or
breaking.
Porcelain
White stoneware, made from clay
prepared from feldspar, china clay, flint and whiting.
Potters Wheel
A device with either a manual (foot
powered) or an electric rotating wheel head used to sit at and
make pottery forms.
Pug
To mix.
Pug Mill
A machine for mixing clay and
recycling clay.
Reduction - Firing with reduced oxygen in
the kiln.
Rib
A rubber, metal or wooden tool used
to facilitate wheel throwing of pottery forms.
Satin Glaze
A glaze with medium reflectance,
between matt and gloss.
Slab
Pressed or rolled flat sections of
clay used in hand building.
Slip
Clay mixed with water with a
mayonnaise consistency. Used in casting and decoration.
Slurry
A thick slip.
Soaking
Maintaining a low steady heat in the
early stages of firing to achieve a uniform temperature throughout
the kiln.
Stacking
Load a kiln to hold the maximum
number of pieces.
Stain
Oxide and water, used as a colorant
for bisque wear.
Stoneware - All ceramic wear fired between
2,100 and 2,300 degrees.
Transparent Glaze
Transmits light clearly.
Throwing
Creating ceramic shapes on the
potter’s wheel.
Vitrification
The firing of pottery to the point
of glossification.
Wedging
A method of kneading clay to make it
homogenous by cutting and rolling.
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