Glassblowing

Glassblowing is a glassforming technique that involves inflating molten glass into a bubble (or parison), with the aid of a blowpipe (or blow tube). A person who blows glass is called a glassblower, glassmith, or gaffer. A lampworker manipulates glass with the use of a torch on a smaller scale, such as in producing precision laboratory glassware out of borosilicate glass.

Technology

Principles

As a novel glass forming technique created in the middle of the last century BC, glassblowing exploited a working property of glass which was previously unknown to the glassworkers: inflation. Inflation refers to the expansion of a molten blob of glass by introducing a small amount of air to it. This property is based on the liquid structure of glass where the atoms are held together by strong chemical bonds in a disordered and random network, therefore molten glass is viscous enough to be blown and gradually hardens as it loses heat.

In order to increase the stiffness of the molten glass, which in turn facilitates the process of blowing, there was a subtle change in the composition of glass. With reference to their studies of the ancient glass assemblages from Sepphoris of Israel, Fischer and McCray postulated that the concentration of natron, which acts as flux in glass, is slightly lower in blown vessels than those manufactured by casting. Lower concentration of natron would have allowed the glass to be stiffer for blowing.

Glass

Glass is a non-crystalline amorphous solid that is often transparent and has widespread practical, technological, and decorative usage in, for example, window panes, tableware, and optoelectronics. Scientifically, the term "glass" is often defined in a broader sense, encompassing every solid that possesses a non-crystalline (that is, amorphous) structure at the atomic scale and that exhibits a glass transition when heated towards the liquid state.

The most familiar, and historically the oldest, types of glass are based on the chemical compound silica (silicon dioxide), the primary constituent of sand. The term glass, in popular usage, is often used to refer only to this type of material, which is familiar from use as window glass and in glass bottles. Of the many silica-based glasses that exist, ordinary glazing and container glass is formed from a specific type called soda-lime glass, composed of approximately 75% silicon dioxide (SiO₂), sodium oxide (Na₂O) from sodium carbonate (Na₂CO₃), calcium oxide, also called lime (CaO), and several minor additives. A very clear and durable quartz glass can be made from pure silica which is very tough and resistant to thermal shock, being able to survive immersion in water while red hot. However, quartz must be heated to well over 3,000 °F (1,650 °C) (white hot) before it begins to melt, and it has a very narrow glass transition, making glassblowing and hot working difficult. In glasses like soda lime, the other compounds are used to lower the melting temperature and improve the temperature workability of the product at a cost in the toughness, thermal stability, and optical transmittance.

Generic top-level domain

Generic top-level domains (gTLDs) are one of the categories of top-level domains (TLDs) maintained by the Internet Assigned Numbers Authority (IANA) for use in the Domain Name System of the Internet. A top-level domain is the last label of every fully qualified domain name. They are called generic for historic reasons; initially, they were contrasted with country-specific TLDs in RFC 920.

The core group of generic top-level domains consists of the com, info, net, and org domains. In addition, the domains biz, name, and pro are also considered generic; however, these are designated as restricted, because registrations within them require proof of eligibility within the guidelines set for each.

Historically, the group of generic top-level domains included domains, created in the early development of the domain name system, that are now sponsored by designated agencies or organizations and are restricted to specific types of registrants. Thus, domains edu, gov, int, and mil are now considered sponsored top-level domains, much like the themed top-level domains (e.g., jobs). The entire group of domains that do not have a geographic or country designation (see country-code top-level domain) is still often referred to by the term generic TLDs.

Glass (film)

Glass (Dutch: Glas) is a 1958 Dutch short documentary film by director and producer Bert Haanstra. The film won the Academy Award for Documentary Short Subject in 1959. The film is about the glass industry in the Netherlands. It contrasts the handmade crystal from the Royal Leerdam Glass Factory with automated bottle making machines. The accompanying music ranges from jazz to techno. Short segments of artisans making various glass goods by hand are joined with those of mass production. It is often acclaimed to be the perfect short documentary.

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