Lead glass

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We are Jinhua Guanghua Printing & Clothing Co., Ltd., which was founded in 2002. It is a Sino-foreign..And you can see more from custom key chain chinese mini atv safety warning signs Laptop Network Card sodium acetate trihydrate metallized film polypropylene automatic floor scrubber hard water cleaner Bike Engine Kit This page may be too technical for a general audience. Please help improve the page by providing more context and better explanations of technical details, even for subjects that are inherently technical. (16 February 2009)Cut lead crystal.Glass consists of a network former, typically silica (SiO2), and network modifiers, including alkali fluxes such as potassium oxide or sodium oxide, and a stabilizer, typically calcium oxide. Lead oxide acts as both a flux and a stabilizer. Lead glass forms part of the silica-potassium-lead system, where lead replaces the calcium content of typical potash glasses.[1] Lead glass contains typically 1835 mol% PbO, whilst modern lead crystal, historically also known as flint glass due to the original silica source, contains a minimum of 24% lead oxide.[2] Technically, the term crystal should never be applied to glass, as glass by definition lacks a crystalline structure, but the use of the term lead crystal remains popular due to historical and commercial reasons, originally stemming from the Venetian use of the word cristallo to describe the rock crystal imitated by Murano glassmakers. This is a naming convention which has been maintained to the present day to describe decorative hollowware.[3]Contents1 Properties 2 History 3 Lead glazes 4 Lead crystal 5 Safety 6 See also 7 References // PropertiesThe addition of lead oxide to glass raises its refractive index and lowers its working temperature and viscosity. The optical properties of lead glass result from the high density of the material. This is due to the presence of lead itself, having a very high atomic weight of 207.2, versus 40.08 for calcium. The density of glass is naturally dependent upon the composition of the glass and varies widely, between 2400 for soda glass to 5900 kg/m3 for high-lead glasses. Whilst soda glasses have a specific gravity below 2.4, that of crystal glass is around 3.1, and may reach values over 4.0.[1]The brilliance of lead crystal relies on the high refractive index (RI) caused by lead oxide. Ordinary glass has a refractive index of n=1.5, whereas the addition of lead produces a range up to 1.7.[1] This heightened RI also raises the correlating index of dispersion, which measures the degree to which a medium separates light into its component spectra, as in a prism. This is why high-lead glass is favoured for achromatic lenses. Cut crystal decorating techniques exploit these properties to create its brilliant, sparkling qualities as each cut facet reflects and transmits light through the object.The addition of lead oxide to potash glass also reduces its viscosity, rendering it more fluid than ordinary soda glass above softening temperature (about 600 ), with a working point of 800 . The viscosity of glass varies radically with temperature, but that of lead glass is roughly 100 times less than that of ordinary soda glasses across working temperature ranges (up to 1100 ). From the glassmaker perspective, this results in two practical developments. First, lead glass may be worked at a lower temperature, leading to its use in enamelling, and second, clear vessels may be made free from trapped air bubbles with considerably less difficulty than with ordinary glasses, allowing the manufacture of perfectly clear, flawless objects. When tapped, lead crystal rings, unlike ordinary glasses. Consumers still rely on this property to distinguish it from cheaper glasses. Since the potash ions are bound more tightly in a lead-silica matrix than in a soda-lime glass, the glass when struck absorbs less energy. This causes the glass to oscillate, thereby producing its characteristic sound.[1] Lead also increases the solubility of tin, copper, and antimony, leading to its use in colored enamels and glazes.HistoryLead may be introduced into glass either as an ingredient of the primary melt or added to preformed leadless glass or frit. The lead oxide used in lead glass could be obtained from a variety of sources. In Europe, galena, PbS, was widely available, which could be smelted to produce metallic lead. The lead metal would be calcined to form PbO by roasting it and scraping off the litharge. In the medieval period lead metal could be obtained through recycling from abandoned Roman sites and plumbing, even from church roofs. Metallic lead was demanded in quantity for silver cupellation, and the resulting litharge could be used directly by glassmakers. Metalworkers and glassmakers required ceramic crucibles, and lead was needed for ceramic lead glazes. This material interdependence suggests a close working relationship between potters, glassmakers, and metalworkers.[4]Lead oxide additives first appear in Mesopotamia, the birthplace of the glass industry.[3] The earliest known example is a blue glass fragment from Nippur dated to 1400 BC containing 3.66% PbO, and is...(and so on)


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