Attività

The word glass comes from the Teutonic term “Glaza”, which means amber. Although the origin of glass production line is still uncertain, the Mesopotamians from the 5th century BC discovered an ash by chance when they fire to melt clay vessel to use for glazing ceramics or when copper was smelted. In Egypt, greenish glass beads were excavated in some of the Pharaohs’’ burial chambers dating from the early 4th century BC, and this has been referred to as intentional glass manufacture. From the second century BC, the production of rings and small figures by using core-wound techniques began to appear. The oldest blueprint for glass was made on clay tablets in 669-627 BC, which read: “Take 60 parts sand, 180 parts ash from marine plants, and 5 parts chalk”. This blueprint is now held in the great library of the Assyrian king, Ashurbanipal, in Nineveh.

The invention of the Syrian blowing iron around 200 BC by Syrian craftsmen enabled the production of thin-walled hollow vessels in a wide variety of shapes. Excavations have revealed that in the Roman era glass was used for the first time as part of the building envelope of public baths in Herculaneum and Pompeii. These panes could have been installed in a bronze or wood surround or without a frame. In the middle ages, this technique spread to the northern Alpine regions, and utensils like drinking horns, claw beakers, and mastos vessels started to be produced; in addition, the use of glass increased in the building of churches and monasteries.
The rollers can be engraved to give the required surface design or texture and produce patterned glass. The glass can be given two smooth surfaces, one smooth and one textured, or two textured sides, depending on the design. In addition, a steel wired mesh can be sandwiched between two separate ribbons of glass to produce wired glass. Wired glass can keep most of glass pieces together after breakage, and it is therefore usually used as fire protection glass.

Viscosity constantly increases during the cooling of liquid glass, until solidification occurs at about 1014 Pas. The temperature at solidification, called the glass transition temperature, is about 530°C for SLSG.

The glass actually freezes, and no crystallization takes place. The extremely cooled liquid nature of glass means that, unlike most solids, the electrons cannot absorb energy to move to another energy level and are strictly confined to a particular energy level. Therefore, the molecules will not absorb enough energy to dissipate energy in ultra violet, infrared or visible bandwidths. However due to some impurities in SLSG, the glass could be greenish or brownish due to Fe2+ and Fe3+ respectively.

Extra clear glass, called low iron glass, which has a reduced amount of iron oxides, is commercially available.

The physical properties of glass mainly depend on the glass type. At room temperature, the dynamic viscosity of glass is about 1020 dPas, a very high amount bearing in mind that water is 1 dPas and honey is 105 dPas. With this high viscosity at room temperature, it could take more than an earth age for flow effects to be visible to the naked eye. Although some observation have shown that in old churches glass panes are thicker at the bottom than at the top, and have referred to this as flow, it is actually because of the glass manufacturing process at the time which was reliant on centripetal force relaxing (crown glass process), making the centre much thinner than the outer parts; in addition, when being installed, the thinner part was usually placed at the top for better visual sparkle and stability.