Lead glass is a variety of glass in which lead replaces the calcium content of a typical potash glass. Lead glass contains typically 18–40 weight% lead(II) oxide (PbO), while modern lead crystal, historically also known as ''flint glass'' due to the original silica source, contains a minimum of 24% PbO. Lead glass is desirable owing to its decorative properties.

Technically, the term ''crystal'' is not applied to glass, as glass, by definition, lacks a crystalline structure. The use of the term ''lead crystal'' remains popular for historical and commercial reasons, and originally stems from the Venetian use of the word ''cristallo'' to describe the rock crystal imitated by Murano glassmakers. This naming convention has been maintained to the present day to describe decorative hollow-ware.

Properties

The addition of lead oxide to glass raises its refractive index and lowers its working temperature and viscosity. The attractive optical properties of lead glass result from the high content of the heavy metal lead. The high atomic number of lead also raises the density of the material, since lead has a very high atomic weight of 207.2, versus 40.08 for calcium. The density of soda glass is 2.4 g/cm³ or below, while typical lead crystal has a density of around 3.1 g/cm³ and high-lead glass can be over 4.0 g/cm³ or even up to 5.9 g/cm³.

The brilliance of lead crystal relies on the high refractive index caused by the lead content. Ordinary glass has a refractive index of n = 1.5, while the addition of lead produces a range up to 1.7. This heightened refractive index also correlates with increased dispersion, which measures the degree to which a medium separates light into its component spectra, as in a prism. Crystal cutting techniques exploit these properties to create a brilliant, sparkling effect as each cut facet reflects and transmits light through the object. The high refractive index is useful for lens making, since a given focal length can be achieved with a thinner lens. However, the dispersion must be corrected by other components of the lens system if it is to be achromatic.

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 °C), with a working point of 800 °C. 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 °C). From the glassmaker’s 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 potassium 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. Lead also increases the solubility of tin, copper, and antimony, leading to its use in colored enamels and glazes. The low viscosity of lead glass melt is the reason for typically high lead oxide content in the glass solders.

The presence of lead is used in glasses absorbing gamma radiation and X-rays, used in radiation shielding (e.g. in cathode ray tubes, where lowering the exposure of the viewer to soft X-rays is of concern).

The high ionic radius of the Pb²⁺ ion renders it highly immobile in the matrix and hinders the movement of other ions; lead glasses therefore have high electrical resistance, about two orders of magnitude higher than soda-lime glass (10^8.5 vs 10^6.5 Ohm·cm, DC at 250 °C). Lead-containing glass is therefore frequently used in light fixtures.

use	! PbO (wt.%)
Household "crystal" leaded glass	18–38
Ceramic glazes and vitreous enamels	16–35
High refractive index optical glasses	4–65
Radiation shielding	2–28
High electrical resistance	20–22
Glass solders and sealants	56–77

History

Lead 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, lead sulfide, was widely available, which could be smelted to produce metallic lead. The lead metal would be calcined to form lead oxide 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. Lead was also used for ceramic lead glazes. This material interdependence suggests a close working relationship between potters, glassmakers, and metalworkers.

Lead oxide additives first appear in Mesopotamia, the birthplace of the glass industry. The earliest known example is a blue glass fragment from Nippur dated to 1400 BC containing 3.66% PbO, and is mentioned in clay tablets from the reign of Assurbanipal (668–631 BC), and a recipe for lead glaze appears in a Babylonian tablet of 1700 BC. A red sealing-wax cake found in the Burnt Palace at Nimrud, from the early C6 BC, contains 10% PbO. These low values suggest that lead oxide may not have been consciously added, and was certainly not used as the primary fluxing agent in ancient glasses. Lead glass also occurs in Han-period China (206 BC – 220 AD). Here it was used in cast to imitate jade, both for ritual objects such as big and small figures, as well as jewellery and a limited range of vessels. Since glass occurs at such a late date in China, it is thought that the technology was brought along the Silk Road by glassworkers from the Middle East. The fundamental compositional difference between Western silica-natron glass and the unique Chinese lead glass, however, may indicate a quite different development.

In medieval and early modern Europe lead glass was used as a base in coloured glasses, specifically in mosaic tesserae, enamels, stained-glass painting, and ''bijouterie'', where it was used to imitate precious stones. Several textual sources describing lead glass survive. In his ''Schedula Diversarum Artium'' (''List Sundry Crafts'''), Theophilus describes its use as imitation gemstone, and the title of a lost chapter mentions the use of lead in glass. The 12–13th century Heraclius details the manufacture of lead enamel and its use for window painting in his ''De Coloribus et artibus Romanorum'' (''Of for Huereds and Crafts Romans'''). This refers to lead glass as “Jewish glass”, perhaps indicating its transmission to Europe. A manuscript preserved at San Marco, Venice, describes the use of lead oxide in enamels and includes recipes for calcining lead to form the oxide. Lead glass was ideally suited for enamelling vessels and windows owing to its lower working temperature than the forest glass body.

Antonio Neri devoted his entire book four of his ''L’Arte Vetraria'' to lead glass, first published in 1612. In this first systematic treatise on glass, he again refers to the use of lead glass in enamels, glassware, and for the imitation of precious stones. Christopher Merrett translated this into English in 1662 (''The Art of Glass''), paving the way for the production of English lead crystal glass by George Ravenscroft.

George Ravenscroft (1618–1681) was the first to produce clear lead crystal glassware on an industrial scale. The son of a merchant with close ties to Venice, Ravenscroft had the cultural and financial resources necessary to revolutionise the glass trade, allowing England to overtake Venice as the centre of the glass industry in the eighteenth and nineteenth centuries. With the aid of Venetian glassmakers, especially da Costa, and under the auspices of the Glass Sellers Guild, Ravenscroft sought to find an alternative to Venetian ''cristallo''. His use of flint as the silica source has led to the term flint glass to describe these crystal glasses, despite his later switch to sand. At first, his glasses tended to crizzle, developing a network of small cracks destroying its transparency, which was eventually overcome by replacing some of the potash flux with lead oxide to the melt, up to 30%. Crizzling results from the destruction of the glass network by an excess of alkali, and may be caused by excess humidity as well as inherent defects in glass composition. He was granted a protective patent in 1673, where production and refinement moved from his glasshouse on the Savoy to the seclusion of Henley-on-Thames, and in 1676, having apparently overcome the crizzling problem, was granted the use of a raven’s head seal as a guaranty of quality. In 1681, the year of his death, the patent expired and operations quickly developed amongst several firms, where by 1696 twenty-seven of the eighty-eight glasshouses in England were producing flint glass containing 30–35% PbO, especially at London and Bristol.

At this period, glass was sold by weight, and the typical forms were rather heavy and solid with minimal decoration. Such was its success on the international market, however, that in 1746 the British Government imposed a lucrative tax by weight. Rather than drastically reduce the lead content of their glass, manufacturers responded by creating highly-decorated, smaller, more-delicate forms, often with hollow stems, known to collectors today as ''Excise glasses''. In 1780, the Government granted Ireland free trade in glass without taxation. English labour and capital then shifted to Dublin and Belfast, and new glassworks specialising in cut glass were installed in Cork and Waterford. In 1825, the tax was renewed, and gradually the industry declined until the mid-nineteenth century, when they were finally repealed.

From this period, English lead glass became popular throughout Europe, and was ideally suited to the new taste for wheel-cut glass decoration perfected on the Continent owing to its relatively soft properties. In Holland, local engraving masters such as David Wolff and Frans Greenwood stippled imported English glassware, a style that remained popular through the eighteenth century. Such was its popularity in Holland that the first Continental production of lead-crystal glass began there, probably as the result of imported English workers. Imitating lead-crystal ''à la façon d’Angleterre'' presented technical difficulties, as the best results were obtained with covered pots in a coal-fired furnace, a particularly English process requiring specialised cone-furnaces. Towards the end of the eighteenth century, lead-crystal glass was being produced in France, Germany, and Norway. By 1800, Anglo-Irish lead crystal had overtaken lime-potash glasses on the Continent, and traditional glassmaking centres in Bohemia began to focus on colored glasses rather than compete directly against it.

The development of lead glass continued through the twentieth century, when in 1932 scientists at the Corning Glassworks, New York, developed a new lead glass of high optical clarity. This became the focus of Steuben glassworks, a division of Corning, which produced decorative vases, bowls, and glasses in Art Deco style. Lead-crystal continues to be used in industrial and decorative applications.

Lead glazes

The fluxing and refractive properties valued for lead glass also make it attractive as a pottery or ceramic glaze. Lead glazes first appear in first century BC to first century AD Roman wares, and occur nearly simultaneously in China. They were very high in lead, 45–60% PbO, with a very low alkali content, less than 2%. From the Roman period, they remained popular through the Byzantine and Islamic periods in the Near East, on pottery vessels and tiles throughout medieval Europe, and up to the present day. In China, similar glazes were used from the twelfth century for colored enamels on stoneware, and on porcelain from the fourteenth century. These could be applied in three different ways. Lead could be added directly to a ceramic body in the form of a lead compound in suspension, either from galena (PbS), red lead (Pb₃O₄), white lead (2PbCO₃·Pb(OH)₂), or lead oxide (PbO). The second method involves mixing the lead compound with silica, which is then placed in suspension and applied directly. The third method involves fritting the lead compound with silica, powdering the mixture, and suspending and applying it. The method used on a particular vessel may be deduced by analysing the interaction layer between the glaze and the ceramic body microscopically.

Tin-opacified glazes appear in Iraq in the eighth century AD. Originally containing 1–2% PbO, by the eleventh century high-lead glaze had developed, typically containing 20–40% PbO and 5–12% alkali. These were used throughout Europe and the Near East, especially in Iznik ware, and continue to be used today. Glazes with even-higher lead content occur in Spanish and Italian maiolica, with up to 55% PbO and as low as 3% alkali. Adding lead to the melt allows the formation of tin oxide more readily than in an alkali glaze, which precipitates into crystals in the glaze as it cools, creating its opacity.

The use of lead glaze has several advantages over alkali glazes in addition to their greater optical refractivity. Lead compounds in suspension may be added directly to the ceramic body. Alkali glazes must first be mixed with silica and fritted prior to use, since they are soluble in water, requiring additional work input. A successful glaze must not ''crawl'', or peel away from the pottery surface upon cooling, leaving areas of unglazed ceramic. Lead reduces this risk by reducing the surface tension of the glaze. It must not craze, forming a network of cracks, nor peel. This is caused when the thermal contraction of the glaze and the ceramic body do not match properly. Ideally, the glaze contraction should be 5–15% less than the body contraction, as glazes are stronger under compression than under tension. A high-lead glaze has a linear expansion coefficient of between 5 and 7×10⁻⁶/°C, compared to 9 to 10×10⁻⁶/°C for alkali glazes. Those of earthenware ceramics vary between 3 and 5×10⁻⁶/°C for non-calcareous bodies and 5 to 7×10⁻⁶/°C for calcareous clays, or those containing 15–25% CaO. Therefore the thermal contraction of lead glaze matches that of the ceramic more closely than an alkali glaze, rendering it less prone to crazing. A glaze should also have a low enough viscosity to prevent the formation of pinholes as trapped gasses escape during firing, typically between 900–1100 °C, but not so high as to run off. The relatively-low viscosity of lead glaze mitigates this issue. It may also have been cheaper to produce than alkali glazes. Lead glass and glazes have a long and complex history, and continue to play new roles in industry and technology today.

Lead crystal

Lead oxide added to the molten glass gives lead crystal a much higher index of refraction than normal glass, and consequently much greater "sparkle" by increasing specular reflection and the range of angles of total internal reflection. Ordinary glass has a refractive index of n = 1.5; the addition of lead produces an index of refraction of up to 1.7. This heightened refractive index 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 increase in refractive index from 1.5 to 1.7 significantly increases the amount of light reflected (by a factor of 1.68 for light reflecting in the normal direction; see Fresnel equations).

In cut glass, which has been hand- or machine-cut with facets, the presence of lead also makes the glass softer and easier to cut. Crystal can consist of up to 35% lead, at which point it has the most sparkle.

Makers of lead crystal objects include

!Name	!Polity
	France
	France
Royal Leerdam Crystal	Netherlands
	United States
Waterford Crystal	Ireland
	Japan
NovaScotian Crystal	Canada
Liuligongfang	Taiwan
Swarovski	Austria
	Czech Republic

Safety

It has been proposed that the historic association of gout with the upper classes in Europe and America was, in part, caused by their extensive use of lead crystal decanters to store fortified wines and whisky. Lin ''et al.'' have statistical evidence linking gout to lead poisoning.

Items made of lead glass may leach lead into the food and beverages contained. In a study performed at North Carolina State University, the amount of lead migration was measured for Port wine stored in lead crystal decanters. After two days, lead levels were 89 µg/L (micrograms per liter). After four months, lead levels were between 2,000 and 5,000 µg/L. White wine doubled its lead content within an hour of storage and tripled it within four hours. Some brandy stored in lead crystal for over five years had lead levels around 20,000 µg/L. To put this into perspective, the U.S. Environmental Protection Agency's lead standard for drinking water is 15 µg/L = 15 parts per billion. Citrus juices and other acidic drinks leach lead from crystal as effectively as alcoholic beverages. When lead-glass beverage containers are used in the ordinary usual way they do not pose a health risk. Under conditions of repeated use of the decanter, the lead leaching steeply decreases with increasing use. This finding is "consistent with ceramic chemistry theory, which predicts that leaching of Pb from crystal is self-limiting exponentially as a function of increasing distance from the crystal-liquid interface." Lead leaching still occurs, but the quantity that leaches into a glass of wine or other beverage let stand for a few hours is much smaller than the quantity of lead consumed daily in ordinary diet. An ordinary diet contains about 70 µg of lead per day.

See also

Steuben Crystal

Waterford Crystal

Edinburgh Crystal

Swarovski

NovaScotian Crystal

List of indices of refraction

Lead

Hot cell

Val Saint Lambert

References

Category:Glass compositions Category:Lead compounds

be:Крышталь cs:Křišťálové sklo de:Bleiglas es:Vidrio de plomo fa:شیشه کریستال fr:Cristal (verre) ko:크리스털 he:בדולח lt:Krištolas hu:Kristályüveg nl:Kristal (glas) ja:クリスタル・ガラス no:Krystallglass pl:Szkło ołowiowe pt:Cristal de chumbo ru:Хрусталь simple:Lead glass fi:Kristalli sv:Kristallglas uk:Кришталь vi:Pha lê

:''For the band, see Glass Harp or for the similar instrument, see Glass harmonica''.

A glass harp (also called musical glasses, singing glasses, angelic organ, verrilion or ghost fiddle) is an instrument made of upright wine glasses.

It is played by running moistened or chalked fingers around the rim of the glasses. Each glass is tuned to a different pitch, either by grinding each goblet to the specified pitch, in which case the tuning is permanent, or by filling the glass with water until the desired pitch is achieved.

History

The glass harp was created in 1741 by Irishman Richard Pockrich, who is known as the first virtuoso of the musical glasses.

The composer Christoph Willibald Gluck played the musical glasses. He performed in London and Copenhagen. His instrument consisted of 26 goblets.

The instrument was popular in the 18th century. Pockrich's contemporary, Ford, published ''Instructions for the Playing of the Musical Glasses'' while Bartl published a German version.

Contemporary uses

On February 18, 1979, Gloria Parker performed as a musical glasses soloist with the Hartford Symphony Orchestra at the Jai Alai Fronton in Hartford, Connecticut, USA. Richard Hayman, noted for his arrangements for Boston Pops conductor Arthur Fiedler, was the guest conductor for the 90-piece orchestra that accompanied the musical glasses which included songs such as ''Lara's Theme'' from the movie ''Dr. Zhivago'', ''Lover'' and ''Amor''.

There are several current musicians who professionally play the glass harp. Among them are the Glass Duo from Poland, Clemens Hofinger in Germany, France's Jean Chatillion and Thomas Bloch, Brien Engel, and Dennis James in the United States and Canada's Real Berthiaume. Glasses have been also used by famous rock band Pink Floyd during the recording of "Shine On You Crazy Diamond" on their ''Wish You Were Here'' album, recorded and released in 1975. Igor Sklyarov played the glass harp on the same song during two 2006 concerts recorded in Venice, Italy by former guitarist David Gilmour. Gilmour also used the effect during his August 26, 2006 concert in Gdańsk, Poland, with the help of Guy Pratt, Phil Manzanera and Dick Parry. Both recordings are available on Gilmour's ''Live in Gdańsk'' CD, although the Venice recording is only available on the 5-disc version of the album or as an internet download with the 3- and 4-disc versions.

''A Toast To Christmas with the Singing Glasses'' is an album recorded and released in 1980, composed and performed by Gloria Parker. Fourteen well-known carols are performed with the glass harp producing flute-like sounds on crystal glasses, marking the first commercial album to use glasses as a musical instrument.

Appearances

In the movie ''Broadway Danny Rose'', directed by Woody Allen, a glass harp is played by Gloria Parker.

In the film ''Miss Congeniality'', Agent Grace Hart plays a glass harp in the talent portion of the fictional Miss United States Pageant.

Gainsborough Dupont, 1775 portrait of Mrs. Philip Thicknesse playing the glasses. She was known as an accomplished musician, especially on the musical glasses.

In the Japanese anime ''Black Butler ll'' a glass armonica and a glass harp set are used to create and combat evil. The armonica makes the people at the ball go crazy and the harps return them to a normal, if confused, state. They appear in both the anime and the manga versions.

A Soundie ''Penthouse Party'' directed and produced by William Forest Crouch featuring Gloria Parker playing the glass harp.

In an MTV short, Lernert Engelbert & Sander Plug are seen playing the hit song ''No Limits'' by 2 Unlimited using a glass harp.

Škoda Auto has commissioned Czech glass harpist Petr Spatina to appear in a television commercial playing 597 Schott Zwiesel crystal wine glasses arranged in the shape of a Škoda Superb

A performance of Mike Oldfield's album ''Tubular Bells III'' features some glass harp playing, as can be seen on the DVD.

In Percy Grainger's work for piano, orchestra, and chorus, ''Tribute to Foster'' (based on Stephen Foster's "Camptown Races"), in the middle lullaby section the members of the chorus are playing tuned wine-glasses to give constant shimmering background notes throughout the whole section of music (lasting a few minutes), making use of a drone effect.

See also

Glass harmonica

Gloria Parker

Glass Duo

Glasso - The Singing Glasses

References

External links

bizbash Water Glasses

glassharp.org

Gloria Parker Musical Glass site

Glass Duo glass harpers official website

Mozart: Adagio and Rondo K.617 for Glassharmonica and Quartet by Glass Duo

Anitras Dans (Anitra's Dance) Video - Third movement of the Suite No. 1 by Edvard Grieg at YouTube played by Glass Duo /glass harp/.

Glass Harp in David Gilmour's Venetian concerts - Glass Harp and "Shine On Your Crazy Diamond"

Grand Harmonicon, Baltimore, ca. 1830 at The Metropolitan Museum of Art

Petr Spatina in Skoda commercial

Category:Friction idiophones Category:Crystallophones Category:1741 in music Category:Melodic percussion

de:Glasharfe es:Copas musicales fr:Verrillon he:נבל זכוכית nds-nl:Glaskern ja:グラス・ハープ pl:Harfa szklana

Thomas Bloch (born 1962 in Colmar, France) is a classical musician specializing in the rare instruments ondes Martenot, glass harmonica, and Cristal Baschet.

Receiving a First Prize for ondes Martenot at the Paris Conservatoire National Supérieur de Musique (with Jeanne Loriod) and a Masters Degree in Musicology at the University of Strasbourg, Bloch has performed over 2500 times and appeared on over eighty recordings. Notable collaborations (concerts or recordings) include Radiohead, John Cage, Damon Albarn / Gorillaz, and Tom Waits / Marianne Faithfull / Bob Wilson.

Biography

Bloch obtained a Master's Degree in Musicology at the University of Strasbourg where he studied with Marc Honegger. He currently lives in Paris, France. He is acknowledged as an expert in the following rare instruments: the glass harmonica, the ondes Martenot and the Cristal Baschet. He has given thousands of performances in forty countries and taken part in more than eighty recordings all over the world. He performs in genres that span classical, contemporary, jazz, rock, ballet, world music, theatre and film score/soundtrack. As a soloist of rare instruments, he plays the complete classical and modern repertoire (including Messiaen, Varèse, and Richard Strauss) and also ten to fifteen premieres from contemporary music each year (Michel Redolfi, Regis Campo, Étienne Rolin, and others) and popular music composers (Jonny Greenwood, Damon Albarn). He also performs in many recording sessions.

Bloch has taught ondes Martenot at the Strasbourg Conservatoire since 1992, is responsible for presentations of instruments at the Paris Musée de la Musique, and is a musical director for music publishers, for the Évian Music Festival (France) and for the Glass Music International Festival 2005 in Paris Cité de la Musique (France).

Performances and appearances

Bloch has performed for numerous movies and is a member of various ensembles. Among his many appearances and performances are the following: ''Amadeus'' (for the 2001 DVD edition), soloist in Milan La Scala (where he gave the first performance of the original version with glass harmonica of ''The Mad Scene'' from Donizetti's ''Lucia di Lammermoor'') during a recital, and a tour with Tom Waits, Bob Wilson and Marianne Faithfull in ''The Black Rider'' (2004–2006).

Awards

Thomas Bloch has been the recipient of some fifteen Conservatoire awards at Colmar, Strasbourg, including a First Prize for ondes Martenot at the Paris Conservatoire National Supérieur de Musique (with Jeanne Loriod). He was praised by critics in several music magazines and also in international composition competitions. Among other awards, he has won: the Classical Music Award 200 given by European critics in Cannes Midem, Victoires de la Musique and Prix de l'Académie Charles Cros, four times best soundtrack during the World subaquatic Movies Festival in Antibes, The Choice of ''Gramophon'', Best of the Year 2001 in ''Audiophile'', and Choc in ''Le Monde de la Musique'' for his interpretation of the ''Turangalîla-Symphonie'' by Messiaen.

Recordings

Bloch has recorded for a number of labels including Columbia, EMI, Erato, and Deutsche Grammophon. Since 1998, he has recorded for Naxos. His recordings include:

''Music for Glass Harmonica'' (8.555295)

''Music for Ondes Martenot'' (8.555779)

Olivier Messiaen's ''Turangalîla-Symphonie'' (8.554478-79)

''Classical Chill'' (8.520101)

''Classical Heat'' (8.520102)

''Mozart : Life and Works'' (8.558061-64)

''Ecuatorial'' by Edgard Varèse

''Missa Cantate'' by Thomas Bloch.

Videos

A large choice of ondes Martenot, glass harmonica and cristal Baschet videos on Youtube played by Thomas Bloch

References

External links

Thomas Bloch's website - including history, videos and pictures of glass harmonica, ondes Martenot, cristal Baschet

Category:Living people Category:French classical musicians Category:Glass harmonica players Category:1962 births Category:People from Colmar Category:Alumni of the Conservatoire de Paris

de:Thomas Bloch es:Thomas Bloch fr:Thomas Bloch pl:Thomas Bloch