Found a good "Glassmaking & Glass Blowing" link? Let Us Know!

A Glossary of Glassmaking Terms This short dictionary is intended to help students and collectors of glass to understand some of the unfamiliar words that they may encounter in books, catalogs, and museum labels. It contains definitions of words and phrases that describe glassmakers' materials, techniques, tools, and products. Words that appear in boldface type in the definitions are defined elsewhere in the dictionary.

Glass Containers Glass manufacture is an old art. Much information is available about glass composition, materials, and general procedures. However, practical experience remains an important factor in the successful operation of a glass plant. Entering glass manufacture is very risky without previous acquaintance with the technology of glass making. Anyone seriously considering it as a business venture is strongly advised to visit some small glass plants. In the United States there are a number of little factories producing glass products on the scale envisioned in this profile. See also: Glass Recycling

NATURAL/VOLCANIC GLASS Glass that is formed by volcanic action is called obsidian and can be found in many parts of the world. Obsidian is formed when the intense heat of a volcano fuses masses of silica together, forming the hard glass. Because of natural impurities, it is usually shiny, black, and opaque, but it can also be very dark red or green; its splinters are often transparent or translucent. Obsidian can be chipped and flaked to make arrow and spearheads, knives, and razors.— DEFINITIONS OF GLASS

GLASSMAKING DISCOVERED / "SECRET INSTRUCTIONS" Little is known about the first attempts to make glass. The Roman historian Pliny attributed it to Phoenician sailors. He recounted how they landed on a beach, propped a cooking pot on some blocks of natron they were carrying as cargo, and made a fire over which to cook a meal. To their surprise, the sand beneath the fire melted and ran in a liquid stream that later cooled and hardened into glass.

CAST AND CUT / CUTTING One of the earliest methods used to make vessels, and decorative objects may have been the technique described below. Compare this method of glass making with CORE FORMING for speed of manufacture. Compare both of these methods with GLASSBLOWING methods.

CORE FORMING One method used by ancient glassmakers to produce small vessels is called the core forming method. A shape made of clay and, probably animal dung, was formed on the end of a metal rod. When it dried, the core was covered with molten glass drawn from a small crucible taken from a furnace.— COLORED GLASS

GLASSBLOWING DISCOVERED Until about 50 B.C. glass objects could only be made slowly. One bottle could take several days to make by casting, core forming, or cutting techniques. Because it was difficult and time-consuming to make, glass was a luxury item as rare as gold or precious stones.

ROMAN LUXURY GLASS /CAGE CUP With the Roman discovery of glassblowing, and the dissemination of the technology, ordinary people could own inexpensive glass objects. The wealthy could afford rare and costly glass objects that were crafted over long periods of time by skilled artisans. Two kinds of Roman luxury glass that are particularly notable are the small number of cage and cameo glass vessels that have survived. Roman cage cups have been known for more than 300 years. The first recorded discovery of one was in 1680 in northern Italy.— CAMEO GLASS

THE "UNBREAKABLE" GLASS OF ANCIENT ROME In the reign of the emperor Tiberius (14-37 AD) a Roman glassmaker demonstrated a remarkable new glass at the imperial court. Unlike ordinary glass, it did not break: it must have seemed almost supernatural. The event was recorded by contemporary writers Pliny and Petronius. They called his glass vitrum flexile (flexible glass). The craftsman displayed a beautiful transparent vase to the emperor and then dashed it to the ground. According to the story, it dented but did not break. Tiberius asked if the glassmaker had told the secret of unbreakable glass to anyone else. When the answer was in the negative, the emperor had the unknown genius put to death and his workshop destroyed fearing that the new material would reduce the value of his imperial gold and silver.

THE MYSTERY SLAB OF BETH SHE'ARIM Glassmaking in ancient times was often carried out in two stages. The first was an engineering stage--the hot, hard, dirty work of heating the granular raw materials to a temperature of about 1100° Celsius in order to bring about the chemical reactions that transformed them into a fluid melt. When the melt cooled down from this near white heat, it set up into a glass.

TYPES OF GLASS Nearly all commercial glasses fall into one of six basic categories or types. These categories are based on chemical composition. Within each type, except for fused silica, there are numerous distinct compositions. GLASS vs. POTTERY/PORCELAIN

PRINCE RUPERT'S DROP AND GLASS STRESS Theoretically, because of the nature of its atomic bonds, glass should be about five times as strong as steel. However, glass tends to have less strength than theory would suggest. One of the main reasons for its loss of strength is surface and internal stress.

SIMPLE GLASS MAKING The common glasses we see in items such as bottles and window panes are made mainly from three crystalline materials: crushed white sand; crushed limestone; and sodium carbonate. Small amounts of other additives are used to improve the glass quality, but these three are the principle elements.

CHEMISTRY OF GLASS — CHEMICAL COUSINS Thousands of different chemical compositions can be made into glass. Different formulas affect the mechanical, electrical, chemical, optical and thermal properties of the glasses that are produced. There is no single chemical composition which characterizes all glass.

FOR A BETTER LANTERN - BORAX Early experiments proved that if the raw materials contained borax, the glass would be far more resistant to heat and temperature change. But the first glasses of this type were so weak chemically that they deteriorated in water.

ANNEALING If a hot glass object is cooled "too quickly," it may be strained at room temperature, and therefore may break easily. For small, or thin-walled shapes (particularly those made of glasses having low expansions) the effect may not be serious. For more massive pieces, the strain can be very serious. The amount of strain (observed in a polariscope) depends upon how quickly the object passes through a critical temperature range. The range depends on the composition of the glass but is usually about 450°C. If the glass is cooled slowly through that range, so that the temperature near the surface is never very different from that of the interior, then the strain in the resulting object is much reduced. . Such glass is said to be Annealed.

RUNNING GLASS/GLASS FLOW One can occasionally hear in art history courses the erroneous idea that "Because glass is a liquid, it flows very slowly. Evidence of this can be seen in Medieval stained glass windows which are thicker at the bottom than they are at the top." This is not true, and the notion behind it is unfounded.

THE MECHANICAL PRESS Making and decorating a piece of glass took a lot of talent, training, and teamwork. In the 1820's, Americans made a pressing machine that needed only two people with little experience (often "street kids") to make it work.—

THE GLASS RIBBON The ribbon machine made electric lights available in virtually every home in America. At the turn of the century, the average American had to work more than four hours to by a single lightbulb. Now the bulb, over 4 times brighter, costs less than 10 minutes pay! Even today, generations after Will Woods conceived his idea, the ribbon machine is considered as one of the world's fastest production devices. Blowing glass bulbs faster than you can channel surf, the ribbon machine has given us a world of light.

GLASS MUSIC After hearing a performance played on musical glasses in England in 1761, Benjamin Franklin set about improving the instrument. He replaced the drinking glasses with custom-blown glass bowls, placed them on their sides and fitted them on a horizontal rod. A treadle turned the assembly, enabling the fingers to rub the exposed rims with a keyboard-like touch. This new design resulted in a more compact size, permanent tuning, and greatly increased technical performance possibilities. With the close spacing of the glass bowls, the player could perform chords and notes in quick succession. Franklin's "glass armonica" is considered to be the first musical instrument invented by an American.

TOOLS Skill, experience, and the tools of the glassmaker—all are needed to produce objects pleasing to both the eye and the hand, part of a centuries-old craft tradition. The tools of the glassmaker, simple in form and few in numkber, are basically the same as those used in the days of the Roman Empire almost 2,000 years ago.

PROPERTIES OF GLASS: Mechanical Mechanical properties deal with the action of forces on a material and the effects that these forces produce within the material.

PROPERTIES OF GLASS: Electrical Conductivity, or the ability to conduct electricity, is the reciprocal of resistivity. Glass, like other insulating materials, provides a high resistance to the passage of electricity. This property is called volume electrical resistivity when it measures the resistance to flow of electricity throughout the body of the glass, and surface electrical resistivity when it measures the resistance of flow along the surface.

PROPERTIES OF GLASS: Optical When a beam of light falls on a piece of glass, some of the light is reflected from the glass surface, some of the light passes through the glass, and some is absorbed in the glass.

PROPERTIES OF GLASS: Thermal Thermal conductivity is stated in the English system in BTU (British Thermal Units) times inches of thickness per hour per square foot of area per degree F. Room-temperature values for glass lie between 4.23 and 10.10, well below the corresponding values for metals. However, in some applications glass equipment will transfer heat more effectively than metal equipment, in spite of the lower thermal conductivity of the glass.

PROPERTIES OF GLASS: Chemical Glass is much more resistant to corrosion than most materials, so much so that it is easy to think of it as corrosion-proof. Glass windows after several years exposure to the elements remain clear and apparently unaffected. Glass bottles hold a wide range of liquids that would dissolve other materials. In the laboratory, reactions are carried out in glass beakers and flasks without damage to the beakers or contamination of the solutions reacting.

WHAT IS GLASS? Glass is a product obtained by the fusion of several inorganic substances, of which normally silica in the form of sand is the main one. The fused mass is cooled to ambient temperature at a rate fast enough to prevent crystallization, i.e., the molecules cannot arrange themselves into a crystalline pattern. The fast rate of cooling to prevent crystallization applies to transparent glasses, whereas in the case of translucent or opal glasses, the rate of cooling is such as to produce a pre-determined level of Crystal formation.

GLASS MELTING FURNACES There are two types of glass melting furnaces.

Glass Forming Process Like treacle and pitch, glass is fluid at high temperature and its fluidity decreases at the temperature is reduced. In other words its viscosity decreases as the temperature increases. Unlike water, which turns from liquid to a solid at a specific temperature, glass has no specific melting or freezing point but is gradually changed from a stiff solid to a liquid mass as the temperature is increased. It is this property of variable viscosity which is utilized in forming a mass of glass into articles of beauty or utility.

Secondary Glass Processing Annealing, toughening, coating & decorating

Glass Uses-Compositions A table with qualities, formulae, and methods of manufacture for varied uses.

Making and working with Glass, from the Glass Encyclopedia Very short articles, but lots of them

Illustrated Glass Dictionary Not as many "illustrations" as the title would have you believe, but some useful info may be gleaned.

Watch fabulous glass objects created step by step. A series of photos. Really doesn't show all that much but it's kind of fun.

Scientific Glassblowing Basics A very good resource, chock full of excellent info & graphics. Only problem is that it is on one of those endless single pages.

History of Stained Glass Based on remains found at Pompeii and Heraculaneum, stained glass was first used by wealthy Romans in their villas and palaces in the first century A.D. At this time stained glass was considered a domestic luxury rather than an artistic medium. It began to be regarded as an art form when Constantine first permitted Christians to worship openly in 313 A.D., as they began to build churches based on Byzantine models. See also: History of Stained Glass and History of Stained Glass

Please Read The Website Disclaimer!
Copyright 1986-2012, The Survival & Self-Reliance Studies Institute (SSRsi), All Rights Reserved
Site conceptualized, designed, created & maintained by MEG Raven
Snail Mail: SSRsi, PO Box 2572 Dillon, CO. 80435-2572

Glass Making Process