The History of glass
Origins of European Glass-making
Ancient and early medieval glass
Glass has arisen gradually during the 4th and 5th millenium B.C. The direct predecessor of glass were glass like glazes that decorated ceramic jewellery and containers. The first glass was made in the east mediterranean and not in Egypt as previously thought. First glass objects were opaque beads of different colors. Such glass artefacts are dated back to the 5th millenium in Syria but in Egypt they do not start to appear before the middle of the 4th millenium. Similarly, the oldest fragments of hollow containers are of an Asian origin - coming from Mezopotamia of the 16th century B.C. Almost all glasses were made 'on a sand core' and their size was about 10 cm. During the 1st century the Syrian glass makers not only exported the glass but they also established glass works outside Syria in Egeian area but also in Italy, France and Rheinland so the Syrian type glass has spread across the entire Roman empire. In the 2nd century they went even further - to Spain, Belgium, Holland, Switzerland and Britain. Therefore the development of glass during the first three centuries A.D. is virtualy the same in the western and eastern part of the mediterranean and only very few types of glass can be considered typical for a particular region. Since the 4th century the shapes of western and eastern products start to differ as the migration of glass makers gradualy stops. Western production further develops decoration already known from the eastern products such as threads (usually with a contrasting colored thread) and different kinds of applicationsand masters it to art. In the 4th and 5th century we can see gradual changes caused by the downfall of the roman culture. Generally it can be said that the roman technological tradition remains until the end of the 1st millenium and then it changes - the soda glass disappears perhaps due to the lack of imported ingredients and the potassium glass appears because it uses local ingrediences (ashes). This change of technology caused the later differences between the glass from countries north of Alps and the glass producted in the mediterranean. In the north the "forest glass" - a greenish potash glass arises from the late Frank glass and soda glass is produced by Italian and other mediterranean regions.
Glass of the Meridian and Late Middle Ages
Hollow glass from meridian and late Middle Ages is practically absent in the archeological material. The only exception is the viking glass from Scandinavia, England and Holland. However, according to the written sources, the main centers of glass production remain glassworks in Rheinland and northern Gallia from where the glass is exported to England, Holland, northern Germany and Scandinavia. Also the woodland region on French - Belgian borders used to belong to places where the medieval production was based on the antic origins. From the 9th to the 12th century the European glass production was typically tied with monasteries which kept the ancient technological knowlege.
Crusades in the 11th century restored the commercial and cultural ties between Near east and Europe and started a gradual development of European glassmaking which occured in the 12th and 13th century. Bottles on paitings in the oldest manuscripts from the 11th and 12th century - typicaly with a ball like body and a long and slender neck - are inspired by a near east products. Such bottles were also found in south France and Italy. In the 12th and 13th century so called forest glassworks start to appear in the central and western europe and they coexist with the monastery glass works. These forest glassworks
were migratory in woodland areas in order to ensure enough firewood. They often were the first settlements in uninhabited mountain areas. Geographical conditions for forest glassworks were optimal in Hessen, Duren and in Bohmerwald. Forest glassworks have mainly produced so called forest glass - a greenish glass with bubbles and dirt which was due to minimum cleaning of the raw material. During the 13 and the 14th century we can observe an increased production of drinking glass. Besides different forms of the Kuttrolf flasks it includes different size cups decorated with various techniques and types of applied decors. This results into famous Krautstrunk known from the 2nd half of the 15th century and it gradually develops into the shape of a Roemer in the 16th century. It is obvious that both roemers and krautstrunks are made of the greenish glass. This tradition has its background in the old opinion that the green glass is especially suitable for serving white Rhoenland wine.
Glass of the 16th - 18th century
North of the Alps forest glass becomes widespread since the 16th century. I central and western Europe it was typically producet in the coutryside using traditional technology and shapes. The forest glassworks producet the greenish forest glass with bubbles, dirt and sand. Rennaissance aspects appear since the 2nd half of the 16th century. Comparing to the expensive Venetian glass the forest glass was affordable to majority. The shapes of central european glass were popular (besides Czech and Germany) in Holland, France and Scandinavia and this lasts to the 18th century. The most common shapes in 16th century are keg like kraurstrunk, roemer and tall cylindrical glass called stangenglas. These tall glasses were decorated with a glass thread wound in a spiral or in horizontal rings assigning each drinker his part as the glass was passed around the table. goblets with a wide routd cup and a bell shaped hollow foot are called roemers. This word perhaps comes from the ancient oremen which means to celebrate. Originaly it was a glass for toasts. Since 1630 roemers do have applied glass decors resembling blackberries which later become typical for roemer glass. Roemers also widely appear on the Dutch paintings from the 16th and 17th century. So called Daumenglass belongs among less usuall German glasses of the 17th century. It is a glass with several small pits that fit the drinkers fingers and prevent the glass from slipping.
Bottles were often used to drink from directly as seen on many middle age paintings. very popular bottle was so called kuttrolf or angster, which was a bottle with a twisted neck consisting of two or more pipes ending with a single opening. It has a Syrian origin. Originally, these bottles served as flacons for parfumes and they kept this role in south europe. they become widespread in Germany and served as a drinking bottle. It is first noted in the german epos Willehalma from 1220 as a gutteral for wine. In Spessart was documented a mass production of kuttrolf bottles in 1409. Kuttrolfs were widely used for wine and spirit until 17th century and less frequently untill 19th century.
How the Glass is made
Glass is made by melting silicate sand together with alcalic additives which faciliate melting. Chemically it is an silicon dioxide (70-75% ) together with sodium or potassium oxide. Other very important comound is the calcium oxide which stabilizes it. The properties of glass vary with its composition. Soda glass is soft and plastic, it stiffs slowly and so it can be shaped and decorated into complicated forms. All antic glass was soda glass as well as the Venezian glass from the 15th to the 18th century. Potash glass is harder. Originally it was used for the greenish forest glass and after mastering the technology of cleaning and decoloring also for the crystal glass.
The natural colour of glass is (depending on the type and amount of unwanted contaminating substances - usually the oxides of iron) greenish or brownish. A clear glass can be obtained only by cleaning and decoloring. Metal oxides dye the glass in various ways. Iron dyes it - depending on the oxidation number - green or brown, copper green, blue and red, cobalt yields blue coloration, gold gives dark red, nickel and manganese purple, chromium and uranium green, sulfur provides yellow color.
Blowing pipe was invented before A.D. and it became the basic glassmaking tool and remained unchanged untill these days. With this invention, the glass production became easy, fast and cheaper. The glassmaker took the hot and fluid glass on the hollow pipe and by blowing into it and rolling it on a marble desk he shaped a glass bubble. This buuble was further heated so it stayed soft, and it was shaped using a variety of tools and in a mould and it was a common origin of every glass product. Such bubble can be decorated with colored glass, it can be spinned into a window plate or it can be blown into a two part wooden mould which gives it its final shape. So called optical decor is achieved by blowing the glass bubble inside a ribbedor other relief decorated mould and by further blowing ouside the mould this relief looses its plasticity and is apparent only by its optical effect. Glass is also typically decorated with in-molten glass fibre, smooth or split, lobes, grids, etc.
Originally, the glass mass was molten in an open pit ovens but the technology progressed rapidly and very efficient and sophisticated ovens are known from the roman times. Ancient technologies of making glass containers were winding a glass thread on a clay core, welding of small colored glass sticks (millefiori), cuting from a glass block, melting in a two-part mould or the 'lost wax'. Blowing pipe was invented in the 1st century B.C. Written and archeological records on glassmaking in Czech countries come from the 13th century. Both these sources help to reveal the equipment of glassworks, technologies of melting, shaping and marketing the glass products. Though the shape of ovens and other details changed during this long way, the basic principle of glass blowing remains unchanged.