Glassmaking

Mother earth made the very first glass. Obsidian, a product of volcanoes, was utilized in olden days to make knives and arrowheads with razor-sharp chipped sides. To produce glass, sand is melted in a furnace rather than a volcano, but basically the material is the same. The methods of glassmaking that gradually evolved in Mesopotamia or Egypt have changed amazingly little over many thousands of years.

Molten Color: Glassmaking in Antiquity

The first half of this exquisitely illustrated book examines the earliest techniques for making glass, including casting, core-forming, and mosaic. All were used for centuries prior to the development of glass blowing, in which molten glass is inflated at the end of a hollow tube. This technique, which started in the middle of the first century, led to entirely new shapes and decorative approaches. The second half of the book looks at glass made during the Roman imperial period.

The science of glass is complicated, for glass is essentially classed as a liquid (or more particularly a super-cooled liquid). It is theoretically a liquid because it is non-crystalline, in reality it seems solid at normal temperatures. To produce glass, a source of silicon like sand or flint is melted into a free-flowing liquid in which other raw elements are mixed. This forms what is referred to as a ‘batch’. To make the production of glass easier, it is essential to reduce the melting point – the temperature at which the glass starts to flow.

Glass Making Demonstration at Corning Museum of Glass

This is accomplished by adding as a flux-an alkaline material like potash or soda. At around 1300-1500° Celsius the components blend together. To help this fusion a stabilizer for example lime or lead oxide is included, in addition to some crushed up shattered glass known as ‘cullet’. As the mix slowly cools and sets, it takes on its non-crystalline shape. It is during this cooling period, midway between a flowing liquid and a solid mass, that glass can be worked and designed into items of use.

Traditional Glassmaking from Robert Harding

This 10×8 Print features an image chosen by Robert Harding. Estimated image size 254x169mm.

Molten glass, with the consistency of sticky treacle, may either be added into a mold or blown into a bubble. Both of these principal methods were developed in ancient times and basically have evolved little over 2 millennia. Casting is the most ancient method. In Egypt glass hieroglyphics for inlaying or portrait heads of pharaohs were created in molds of clay. In Greece a comparable method produced bowls of amber or blue glass that could be smoothed and polished like stone. The ‘core-form’ technique utilized an internal mold of clay around which thin trails of molten glass were wound. The roughly formed core was then scraped out to make bottles and jugs for valuable unctions.

Glass Masters at Work: William Gudenrath

Photographic Prints of Traditional glassmaking from Robert Harding

The breakthrough discovery of glassblowing was a key improvement that spread through the Roman Empire in the 1st century BC. To form a vessel by blowing, a ‘gather’ of molten glass is collected from the crucible on the end of a long tube made of iron. The design of the gather affects the shape of the blown vessel, and thus before air is blown through the tube, the gather is rolled on a flat iron slab known as a ‘marvering’ table. The bubble, or ‘paraison’, is inflated by gently blowing through the tube. Simultaneously, swinging the blowing iron will stretch out the paraison. A limitless assortment of shapes can be made in this way, their forms determined completely by the skill of the glassblower. Diverse tools are used to shape the paraison, with tongs and shears to pinch or cut the developing vessel and further rolling or marvering to manage the shape and surface.

Glass Blowing Documentary

Engravings of classic glasshouses show that the arrangements inside have also transformed little over hundreds of years. The huge brick cones that are so typical of glass manufactories are built to eliminate the smoke and funnel the air around the central furnace where a draught is directed beneath the fire so that a constant high temperature can be preserved.Within the furnace a set of clay crucibles or ‘pots’ are arranged in a circle and these contain the ‘batch’ of molten glass. The pots are refilled in a regular order, to ensure that there is always a supply of melted glass of the proper consistency for the blowers to use. Above each pot is an opening or ‘glory hole’ through which the glassblowers place their blowing irons to get the gathers.

Glass Throughout Time: History and Technology of Glassmaking from the Ancient World to the Present

Glassblowers work in groups of three or four workers known as a ‘chair’, as usually the senior workman or ‘gaffer’ sat in a uniquely shaped ‘glassmaker’s chair’ with long flat arms along which blowing irons can be rolled. A piece of glass would be passed between various members of the ‘chair’ who in turn would shape the bowl or the foot of the glass being formed. Once the essential shape was built, a solid metal rod or ‘pontil’ was joined to the center of the vessel so that the other end could be cut from the blowing iron. More sensitive finishing and any further trailed decor is generally added when it has been joined to the pontil. Molten glass cools from the moment it leaves the furnace. To keep the glass workable, the partially formed vessel has to be taken back to the furnace and inserted through the glory hole to reheat. When adequately malleable once more, the glass can be removed from the heat and blowing and decorating goes on.

How to Blow Glass

Techniques for blowing glass and starting a project, including tips; learn these things and more in this instructional arts and crafts video series on glass blowing.

Roman glassblowers discovered that paraisons could be inserted into clay molds and blown into predetermined shapes. Wood and metal molds developed later, and in the nineteenth century the commercial implication of mass-production led to factories churning out identical molded glass bottles. Machines take the place of glassblowers and identical measures of molten glass are forced into molds that can be used again and again. Press-molding, where a blob of molten glass is squeezed between two metal dyes, produces cheap but practical dishes, cups or posy vases, available in different colors. There is an assumption that molded glass is cheap and inferior to hand blowing, but good molded glass can be both artistic and infinitely preferable to poorly designed blown glass.

Legend of Bohemian Glass: A Thousand Years of Glassmaking in the hearth of E

Whatever technique is used to shape a piece of glass, it can’t be allowed to cool by itself. Different parts of a vessel and different thicknesses of glass cool down and contract at different rates. This causes uneven stress to build up internally, resulting in unstable vessels that can crack or even shatter as soon as they are used. Back in ancient times it was discovered that a carefully controlled, gradual cooling prevented glass objects from cracking. Glass was placed in a separate ‘Annealing Chamber’ next to the furnace where the heat inside could be reduced very slowly. Annealing tunnels developed through which the cooling glass pieces were slowly drawn until they were further away from the intense heat. Objects can require anything up to sixty hours in the annealing chamber in order to be tough enough to stand regular use. Annealing is an essential part of the manufacture of all glass, including machine-made bottles and windowpanes.

Murano Glass Art

The art of Murano Glass by the Master Pino Signoretto in a great collaboration with the american artist Richard Birt.

A molded pattern or any internal ornament is part of the process of forming, but all other decoration is added separately. Trailed glass ornamentation involving molten glass, or additional layers of colored glass are normally added before annealing, whereas cutting, engraving or any painted decoration is carried out in a separate part of the glass works well away from the furnace. Internal decoration can range from simple bubbles trapped in a line to intricate patterns of spiral twists in the stem of a wineglass or spread throughout a lavish piece of Venetian latticinio glass. In Ancient Egypt mosaic techniques created curious images in colored glass and these led to Roman millefiori bowls that were themselves the inspiration behind Victorian glass paperweights. The Art Nouveau period saw the development of many new integral glass-making techniques including Pate de Vere where the whole piece was constructed using powdered glass of different colors. Many exciting methods of integral decoration, using modern designs and colors, have been used since the 1930s in Scandinavia and in post-war Venice.

Glassmaking: America’s First Industry

Many of the surface decorating methods employed today go back to Roman times, for the Romans discovered wheel cutting, engraving and enamel ling. A rotating wheel of metal or stone will slice a series of facets through the surface of glass with the assistance of lubricating oil and an abrasive powder such as emery. Glasscutters need to be skilled in geometry, for elaborate patterns are marked out on the surface in a series of carefully measured lines. Initial cutting uses a wheel of iron and abrasive sand, followed by smoother stone or wooden wheels and much finer abrasive powders to polish each facet. The wheels are fixed in position while the glasscutters press the vessels to be cut against them. As the glasses are carefully rotated, wonderful sparkling effects are created. Initially hand- or foot-powered treadles drove the wheels.

The development of steam-powered wheels led to more accomplished, deeper cutting in the nineteenth century. Today, electric wheels are in general use, while washes of acidic chemicals replace fine abrasives to provide a totally smooth surface. Tiny revolving copper wheels are used for engraved decoration cut into the surface. Flowers, scenes or inscriptions all rely on the skill of the engraver who sketches the individual design by holding the glass beneath a wheel that is continually fed with oil containing an abrasive. The most detailed engraving uses copper wheels no bigger than a pinhead, while a rather different kind of engraving makes use of the point of a diamond to scratch and stipple a design on the surface of a glass.

Combinations of deep cutting and engraving produce incredible carved effects. In clear glass ‘Rock Crystal’ engraving resembles similar effects carved into hardstones. When layers of different colored glass are carved with fine wheels ‘cameo’ glass is created. Here, instead of engraved designs cut into the surface (intaglio decoration), cameo glass is created by carving away the background to leave the design raised in relief. The Roman technique of cameo glass was revived in the nineteenth century, particularly in Stourbridge.

The Art of Glass Making

Cameo glass involves casing a glass vessel with a layer of glass of a different color. While the Romans carved entirely by hand, in Stourbridge acid was used initially to remove much of the background glass, followed by copper wheel polishing to carve fine detail into the relief. Combinations of acid-resist decoration and wheel polishing created many of the masterpieces of Art Nouveau glass.

Fostoria Glassware, 1887-1982: Identification & Values: 95 Years of Glassmaking

Concentrated hydrofluoric acid was also used to etch patterns into the surface of clear glass. To create acid-etched decoration, patterns were firstly incised through coatings of an acid-resistant wax painted on to the surface. The acid cut into the glass where the wax had been scratched away, creating a design etched to an even depth. Acid etching is cheaper than hand engraving, but in spite of this fine etching can still be artistic and of supreme quality.

Layers of different colored glass are used for many decorating techniques as well as to economize on expensive colored mixes. A very thin coating or ‘flashing’ of colored glass can give a colorless object the appearance of being made of solid red or blue glass for example. When a scene is engraved through a ‘ruby-flashed’ surface the result is a dramatic colored background as practiced to great effect in nineteenth century Bohemia. A thicker casing of colored glass is usually referred to as an ‘overlay’. By cutting through different overlays, very striking patterns are created when the colored layers underneath are revealed.

Stained Glass Making Equipment

The equipment necessary for making stained glass pieces include pattern shears, goggles, a glass cutter, high-quality oil, copper foil and a soldering iron. Gather the essential tools of the trade with helpful instruction from an experienced glass artist in this video on glasswork.

Many different decorative effects can be created by shading glass of different colors. Certain glass is described as heat-sensitive and will change color at specific temperatures. By heating this glass unevenly at the mouth of the glass furnace, graduated color can be achieved. Color can also be applied to the surface in the form of stains, while other chemical treatments can recreate the iridescence that forms on ancient glass after centuries of burial. Metallic lustres and rainbow iridescence enjoyed widespread popularity during the Art Nouveau period.

How It’s Made: Glass Bottles

Discovery / Science Channel’s “How It’s Made” Glass Bottles episode.

Enameling and gilding are techniques associated primarily with the decoration of porcelain. Painting is rarely effective on clear glass although some transparent enamels were used most successfully in Biedermeier Vienna. On opaque or colored glass, however, painted designs and gilding are used in many different ways. Enamels are essentially finely powdered glass mixed with coloring agents. Aided by an added flux, the glass powder melts in an enameling kiln and fuses the color to the surface. Gilding requires a lower temperature to fix it to the surface, and can add the finishing touch to decorative glassware, for brightly burnished gold can bestow incredible richness.

Glassmaking is all about teamwork. Great artists such as Kothgasser, Fritsche, Beilby or Rny relied on experienced glassblowers to create the blank goblets or vases on which they practiced their engraving or enameling. The role of the designer is very important as each stage in the manufacture of a fine piece of glass takes careful planning. Successful glassmakers have to understand marketing in order to create work the public wants to buy. Old-fashioned cut glass patterns will not sell alongside more up-to-date designs; while even the cheapest molded wine bottles require the most complicated planning to create a satisfactory shape and then fashion the machines and the molds from which they are cast. Since ancient times – from big factories or tiny studios, using mechanized processes or artistry by hand – glass is the most versatile of materials. Golden opportunities lie ahead for all collectors who are indeed spoiled for choice.

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