The old Romans had glass
roman glass - vitrum
vitrum - the glass of the Romans
Antique glass is probably in the late 3rd millennium BC. discovered as a coincidental product of ceramic production. In the early stages of glass production, the right mixture of sand / soda / lime occurs naturally and "only" has to be melted. At the same time, the copper smelting seems to have delivered greenish, glassy-transparent slags and precipitates. It took around 500 years before vessels could be made from glass. And only after another 1,500 years was in the 1st century BC. made the groundbreaking discovery that hot glass can be puffed up by air. Even if, according to Pliny the Elder, The cradle of the art of glassmaking is said to be in Palestine, the oldest pieces available to us come from Mesopotamia and Egypt. Early glass objects were rare and valuable. Raw glass was only melted in a few places and traded over long distances. What this trade looked like is largely unknown. Raw glass is a commodity until the 21st century BC. verifiable. Most of the finds are already dyed material.
Apart from the risk of breakage, the material is chemically by no means as stable as one could wish it to be. Many antique glasses were water-soluble due to the lack of sufficient lime and have disappeared. But the pieces that hit us also suffer from so-called weathering. The attacked surface changes color and can form a silvery-white to dull black layer. Even iridescence, which lay people find attractive, is actually flaking off the finest scales with light refraction in bright colors.
Roman vitrum of the imperial era
From the 1st century Glass production increased to such an extent that affluent households often owned glass windows and glass beakers became affordable for large parts of the population. During the Migration Period, knowledge about raw glass production was lost in many provinces and old glasses were recycled. Roman window glass was therefore used in the 5th - 6th centuries. a valued raw product.
Antique glass is made from soda, lime, and silicates. The latter are actually the main ingredient, but have such a high melting point that ancient technology was overwhelmed. By adding alkali (soda), the required temperature was lowered to 1000 ° - 1100 ° C.
The importance of adding lime was apparently not known. Without this, however, the glass mass was water-soluble. Many antique glasses have simply dissolved or are in an unstable condition over time. Wherever impurities in the sand (shell remains, river pebbles) provided the necessary lime content, permanently stable glass masses were created. Many Mesopotamian glass melters seem to have gotten the problem under control by adding calcareous plant ashes.
This technique of glass forming, which was often used in antiquity, has largely been forgotten. At the right temperature, glass has a viscous character that enables it to be deformed. Interesting pieces can be made in conjunction with the classic turntable. The early history of antique glass is a juxtaposition of ceramic and glass pots. No wonder many shapes were done in parallel. It was only in the late Hellenism that glassblowers developed a new formal language that was only adequate for this material. Pottery pieces usually have strong walls and rounded edges, ideal properties for glass for use.
In its simplest form, Roman mosaic glass consists of similar elements. Usually 2 or 3 different elements are used to create a lively structure.
Dating the group presents considerable difficulties. Apparently, very similar pieces were made over a long period of time.
Isings 1 lower round wall shell
Isings 2 bowls with a constricted wall
Isings 3 ribbed bowl
Isings 12 spherical bowl
Mille-Fiori-Glass: The not very sharp name actually does not define a separate group. Structurally, it is a matter of "simple" mosaic glasses, which were put together from multicolored round rod sections. The stretching, which is inevitable during the pottery, is beneficial. The small group is not dated uniformly.
Agate glass: A coveted and particularly valuable look could be achieved through particularly skillful laying out (or spraying?) Of the glass mass. These pieces imitate the extremely expensive agate vessels. Hellenistic forerunners appear in the 2nd century BC. dated, Roman pieces are Julio-Claudian.
Reticella glass: This is a technique similar to mosaic glass. As a special feature, the shapes are built from twisted glass threads and pottery in shape. This requires a lot of skill, precision and speed. Most of the pieces date from the 1st century BC.
Ribbed bowls (Form Isings 3) were very popular between 100 BC and 130 AD. The glass mass was pottered around a curved core and pressed into ribs from above with pieces of wood. Finally, the ribs on the edge of the bowl were pressed flat.
Early pieces are only sometimes multi-colored, but mostly of a strong color, later predominantly transparent, whitish-green.
In the 1st century ribbed bowls are copied. In these cases, it is blown glass (delicate ribbed bowls).
It takes getting used to the idea that ribbed bowls were used as drinking bowls. The flat version (Isings 3a) in particular is unwieldy as a drinking vessel. In the later naturally colored pieces, the high version predominates (Isings 3b). The luxury version of the early rib bowls was made from mosaic glass. It is the flat shape of Isings 3a. Usually dating is done in a Tiberian-Claudian way.
Due to the special glass structure, the manufacturing technique of these bowls is particularly easy to recognize.
While it used to be assumed that the white top layer was cut into shape from a double-layered glass (flashed glass), today we know better: First a plaster model was created with a very fine relief. The hollows were then filled with white glass powder and finally the blue ground was potted over them. The tough glass mass was hot enough to melt the white glass powder. A grinding process that was overwhelming for the technology at the time could thus be dispensed with. The so-called Portland vase in the British Museum, probably the most famous piece of its kind, exemplifies the manufacturing technique. The relief zone was beyond a certain extent not potable. The artist would certainly have gladly avoided the "starved" upper edge.
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