Colored Glasses A report on colored glasses  Author  :Ammar Ahmad   8/30/2010  

Glass Glass is an amorphous (non-crystalline) solid material. Glasses are typically brittle, and often optically transparent. Glass is commonly used for windows, bottles, and eyewear; examples of glassy materials include soda-lime glass, borosilicate glass, acrylic glass, sugar glass, Muscovy-glass, and aluminium oxynitride. The term glass developed in the late Roman Empire. It was in the Roman glassmaking center at Trier, now in modern Germany, that the late-Latin term glesum originated, probably from a Germanic word for a transparent, lustrous substance.

Strictly speaking, a glass is defined as an inorganic product of fusion which has been cooled through its glass transition to the solid state without crystallising. Many glasses contain silica as their main component and glass former. The term "glass" is, however, often extended to all amorphous solids (and melts that easily form amorphous solids), including plastics, resins, or other silica-free amorphous solids. In addition, besides traditional melting techniques, any other means of preparation are considered, such as ion implantation, and the sol-gel method. Commonly, glass science and physics deal only with inorganic amorphous solids, while plastics and similar organics are covered by polymer science, biology and further scientific disciplines.

Glass plays an essential role in science and industry. The optical and physical properties of glass make it suitable for applications such as flat glass, container glass, optics and optoelectronics material, laboratory equipment, thermal insulator (glass wool), reinforcement fiber (glass-reinforced plastic, glass fiber reinforced concrete), and art.

History of glass Origins of glass making

Naturally occurring glass, especially the volcanic glass obsidian, has been used by many Stone Age societies across the globe for the production of sharp cutting tools and, due to its limited source areas, was extensively traded. But in general, archaeological evidence suggests that the first true glass was made in coastal north Syria, Mesopotamia or Old Kingdom Egypt. Because of Egypt's favorable environment for preservation, the majority of well-studied early glass is found there, although some of this is likely to have been imported. The earliest known glass objects, of the mid third millennium BCE, were beads, perhaps initially created as accidental by-products of metal-working slags or during the production of faience, a pre-glass vitreous material made by a process similar to glazing.

During the Late Bronze Age in Egypt (e.g., the Ahhotep "Treasure") and Western Asia (e.g. Megiddo) there was a rapid growth in glass-making technology. Archaeological finds from this period include colored glass ingots, vessels (often colored and shaped in imitation of highly prized hardstone carvings in semi-precious stones) and the ubiquitous beads. The alkali of Syrian and Egyptian glass was soda ash, sodium carbonate, which can be extracted from the ashes of many plants, notably halophile seashore plants: (see saltwort). The earliest vessels were 'core-wound', produced by winding a ductile rope of glass round a shaped core of sand and clay over a metal rod, then fusing it with repeated reheatings. Threads of thin glass of different colors made with admixtures of oxides were subsequently wound around these to create patterns, which could be drawn into festoons by using metal raking tools. The vessel would then be rolled flat ('marvered') on a slab in order to press the decorative threads into its body. Handles and feet were applied separately. The rod was subsequently allowed to cool as the glass slowly annealed and was eventually removed from the center of the vessel, after which the core material was scraped out. Glass shapes for inlays were also often created in moulds. Much early glass production, however, relied on grinding techniques borrowed from stone working. This meant that the glass was ground and carved in a cold state.

By the 15th century BCE extensive glass production was occurring in Western Asia, Crete and Egypt and the Mycenaean Greek term ku-wa-no-wo-ko meaning "worker of lapis lazuli and glass" (written in Linear b syllabic script) is attested. It is thought the techniques and recipes required for the initial fusing of glass from raw materials was a closely guarded

technological secret reserved for the large palace industries of powerful states. Glass workers in other areas therefore relied on imports of pre-formed glass, often in the form of cast ingots such as those found on the Ulu Burun shipwreck off the coast of modern Turkey.

Glass remained a luxury material, and the disasters that overtook Late Bronze Age civilizations seem to have brought glass-making to a halt. It picked up again in its former sites, in Syria and Cyprus, in the ninth century BCE, when the techniques for making colorless glass were discovered. The first glassmaking "manual" dates back to ca. 650 BCE. Instructions on how to make glass are contained in cuneiform tablets discovered in the library of the Assyrian king Ashurbanipal. In Egypt glass-making did not revive until it was reintroduced in Ptolemaic Alexandria. Core-formed vessels and beads were still widely produced, but other techniques came to the fore with experimentation and technological advancements. During the Hellenistic period many new techniques of glass production were introduced and glass began to be used to make larger pieces, notably table wares. Techniques developed during this period include 'slumping' viscous (but not fully molten) glass over a mould in order to form a dish and 'millefiori' (meaning 'thousand flowers') technique, where canes of multi-colored glass were sliced and the slices arranged together and fused in a mould to create a mosaic-like effect. It was also during this period that colorless or decolored glass began to be prized and methods for achieving this effect were investigated more fully.

According to Pliny the Elder, Phoenician traders were the first to stumble upon glass manufacturing techniques at the site of the Belus River. Georgius Agricola, in De re metallica, reported a traditional serendipitous "discovery" tale of familiar type:

"The tradition is that a merchant ship laden with nitrum being moored at this place, the merchants were preparing their meal on the beach, and not having stones to prop up their pots, they used lumps of nitrum from the ship, which fused and mixed with the sands of the shore, and there flowed streams of a new translucent liquid, and thus was the origin of glass."

This account is more a reflection of Roman experience of glass production, however, as white silica sand from this area was used in the production of Roman glass due to its low impurity levels.

During the first century BCE glass blowing was discovered on the Syro-Palestinian coast, revolutionising the industry and laying the way for the growth of glass production that occurred throughout the Roman world. It was the Romans who began to use glass for

architectural purposes, with the discovery of clear glass (through the introduction of manganese oxide), in Alexandria ca. AD 100. Cast glass windows, albeit with poor optical qualities, thus began to appear in the most important buildings in Rome and the most luxurious villas of Herculaneum and Pompeii. Over the next 1,000 years glass making and working continued and spread through southern Europe and beyond.

History by culture

India (Hindu Kingdoms)

ndigenous development of glass technology in South Asia may have begun in 1730 BCE. Evidence of this culture includes a red-brown glass bead along with a hoard of beads dating to that period, making it the earliest attested glass from the Indus Valley locations. Glass discovered from later sites dating from 600–300 BCE displays common color.

Chalcolithic evidence of glass has been found in Hastinapur, India. Some of the texts which mention glass in India are the Shatapatha Brahmana and Vinaya Pitaka. However, the first unmistakable evidence in large quantities, dating from the 3rd century BCE, has been uncovered from the archaeological site in Takshashila, ancient India.

By the first century C.E., glass was being used for ornaments and casing in South Asia. Contact with the Greco-Roman world added newer techniques, and Indians artisans mastered several techniques of glass molding, decorating and coloring by the succeeding centuries. The Satavahana period of India also produced short cylinders of composite glass, including those displaying a lemon yellow matrix covered with green glass.

Romans

Roman glass objects have been recovered across the Roman Empire in domestic, industrial and funerary contexts. Glass was used primarily for the production of vessels, although mosaic tiles and window glass were also produced. Roman glass production developed from Hellenistic technical traditions, initially concentrating on the production of intensely colored cast glass vessels. However, during the first century AD the industry underwent rapid technical growth that saw the introduction of glass blowing and the dominance of colorless or ‘aqua’ glasses. Production of raw glass was undertaken in geographically separate locations to the working of glass into finished vessels, and by the end of the first century AD large scale manufacturing resulted in the establishment of glass as a commonly available material in the Roman world.

Anglo-Saxon world Anglo-Saxon glass has been found across England during archaeological excavations of both settlement and cemetery sites. Glass in the Anglo-Saxon period was used in the manufacture of a range of objects including vessels, beads, windows and was even used in jewelry. In the 5th century AD with the Roman departure from Britain, there were also considerable changes in the usage of glass. Excavation of Romano-British sites have revealed plentiful amounts of glass but, in contrast, the amount recovered from 5th century and later Anglo-Saxon sites is minuscule. The majority of complete vessels and assemblages of beads come from the excavations of early Anglo-Saxon cemeteries, but a change in burial rites in the late 7th century affected the recovery of glass, as Christian Anglo-Saxons were buried with fewer grave goods, and glass is rarely found. From the late 7th century onwards, window glass is found more frequently. This is directly related to the introduction of Christianity and the construction of churches and monasteries. There are a few Anglo-Saxon ecclesiastical literary sources that mention the production and use of glass, although these relate to window glass used in ecclesiastical buildings. Glass was also used by the Anglo-Saxons in their jewelry, both as enamel or as cut glass insets.

Islamic world The Arab poet al-Buhturi (820–897) described the clarity of such glass, "Its color hides the glass as if it is standing in it without a container."

Stained glass was also first produced by Muslim architects in Southwest Asia using colored glass rather than stone.[citation needed] In the 8th century, the Persian chemist Jabir ibn Hayyan (Geber) scientifically described 46 original recipes for producing colored glass in Kitab al-Durra al-Maknuna (The Book of the Hidden Pearl), in addition to 12 recipes inserted by al-Marrakishi in a later edition of the book.

By the 11th century, clear glass mirrors were being produced in Islamic Spain.

Medieval Europe Glass objects from the 7th and 8th centuries have been found on the island of Torcello near Venice. These form an important link between Roman times and the later importance of that city in the production of the material. Around 1000 AD, an important technical breakthrough was made in Northern Europe when soda glass, produced from white pebbles and burnt

vegetation was replaced by glass made from a much more readily available material: potash obtained from wood ashes. From this point on, northern glass differed significantly from that made in the Mediterranean area, where soda remained in common use.

Until the 12th century, stained glass – glass to which metallic or other impurities had been added for coloring – was not widely used, but it rapidly became an important medium for Romanesque art and especially Gothic art. Almost all survivals are in church buildings, but it was also used in grand secular buildings.

The 11th century saw the emergence in Germany of new ways of making sheet glass by blowing spheres. The spheres were swung out to form cylinders and then cut while still hot, after which the sheets were flattened. This technique was perfected in 13th century Venice.

The Crown glass process was used up to the mid-19th century. In this process, the glassblower would spin approximately 9 pounds (4 kg) of molten glass at the end of a rod until it flattened into a disk approximately 5 feet (1.5 m) in diameter. The disk would then be cut into panes.

Domestic glass vessels in late medieval Northern Europe are known as Forest glass.

Murano glassmaking The center for luxury Italian glassmaking from the 14th century was the island of Murano, which developed many new techniques and became the center of a lucrative export trade in dinnerware, mirrors, and other items. What made Venetian Murano glass significantly different was that the local quartz pebbles were almost pure silica, and were ground into a fine clear sand that was combined with soda ash obtained from the Levant, for which the Venetians held the sole monopoly. The clearest and finest glass is tinted in two ways: firstly, a natural coloring agent is ground and melted with the glass. Many of these coloring agents still exist today; for a list of coloring agents, see below. Black glass was called obsidianus after obsidian stone. A second method is apparently to produce a black glass which, when held to the light, will show the true color that this glass will give to another glass when used as a dye.

The Venetian ability to produce this superior form of glass resulted in a trade advantage over other glass producing lands. Murano’s reputation as a center for glassmaking was born when the Venetian Republic, fearing fire might burn down the city’s mostly wood buildings, ordered glassmakers to move their foundries to Murano in 1291. Murano's glassmakers were soon the island’s most prominent citizens. Glassmakers were not allowed to leave the

Republic. Many took a risk and set up glass furnaces in surrounding cities and as far afield as England and the Netherlands.

Glass batch calculation

Glass batch calculation or glass batching is used to determine the correct mix of raw materials (batch) for a glass melt.

Principle

The raw materials mixture for glass melting is termed "batch". The batch calculation is based on the common linear regression equation:

NB = (BT·B)-1·BT·NG

with NB and NG being the molarities 1-column matrices of the batch and glass components respectively, and B being the batching matrix. The symbol "T" stands for the matrix transpose operation, "-1" indicates matrix inversion, and the sign "·" means the scalar product. From the molarities matrices N, percentages by weight (wt%) can easily be derived using the appropriate molar masses.

Example calculation

An example batch calculation may be demonstrated here. The desired glass composition in wt% is: 67 SiO2, 12 Na2O, 10 CaO, 5 Al2O3, 1 K2O, 2 MgO, 3 B2O3, and as raw materials are used sand, trona, lime, albite, orthoclase, dolomite, and borax. The formulas and molar masses of the glass and batch components are listed in the following table:

Formula of glass component

Desired concentration of glass component, wt%

Molar mass of glass component, g/mol

Batch component

Formula of batch component

Molar mass of batch component, g/mol

SiO2 67 60.0843 Sand SiO2 60.0843 Na2O 12 61.9789 Trona Na3H(CO3)2*2H2O 226.0262 CaO 10 56.0774 Lime CaCO3 100.0872 Al2O3 5 101.9613 Albite Na2O*Al2O3*6SiO2 524.4460 K2O 1 94.1960 Orthoclase K2O*Al2O3*6SiO2 556.6631 MgO 2 40.3044 Dolomite MgCa(CO3)2 184.4014 B2O3 3 69.6202 Borax Na2B4O7*10H2O 381.3721

The batching matrix B indicates the relation of the molarity in the batch (columns) and in the glass (rows). For example, the batch component SiO2 adds 1 mol SiO2 to the glass, therefore, the intersection of the first column and row shows "1". Trona adds 1.5 mol Na2O to the glass; albite adds 6 mol SiO2, 1 mol Na2O, and 1 mol Al2O3, and so on. For the example given above, the complete batching matrix is listed below. The molarity matrix NG of the glass is simply determined by dividing the desired wt% concentrations by the appropriate molar masses, e.g., for SiO2 67/60.0843 = 1.1151.

The resulting molarity matrix of the batch, NB, is given here. After multiplication with the

appropriate molar masses of the batch ingredients one obtains the batch mass fraction matrix

MB:

The matrix MB, normalized to sum up to 100% as seen above, contains the final batch composition in wt%: 39.216 sand, 16.012 trona, 10.242 lime, 16.022 albite, 4.699 orthoclase, 7.276 dolomite, 6.533 borax. If this batch is melted to a glass, the desired composition given above is obtained. During glass melting, carbon dioxide (from trona, lime, dolomite) and water (from trona, borax) evaporate.

Another simple glass batch calculation can be found at the website of the University of Washington.

Glass production

Glass ingredients Pure silica (SiO2) has a "glass melting point"— at a viscosity of 10 Pa·s (100 P)— of over 2300 °C (4200 °F). While pure silica can be made into glass for special applications (see fused quartz), other substances are added to common glass to simplify processing. One is sodium carbonate (Na2CO3), which lowers the melting point to about 1500 °C (2700 °F) in soda-lime glass; "soda" refers to the original source of sodium carbonate in the soda ash obtained from certain plants. However, the soda makes the glass water soluble, which is usually undesirable, so lime (calcium oxide (CaO), generally obtained from limestone), some magnesium oxide (MgO) and aluminium oxide (Al2O3) are added to provide for a better chemical durability. The resulting glass contains about 70 to 74% silica by weight and is called a soda-lime glass. Soda-lime glasses account for about 90% of manufactured glass.

Most common glass has other ingredients added to change its properties. Lead glass or flint glass, is more 'brilliant' because the increased refractive index causes noticeably more "sparkles", while boron may be added to change the thermal and electrical properties, as in Pyrex. Adding barium also increases the refractive index. Thorium oxide gives glass a high refractive index and low dispersion and was formerly used in producing high-quality lenses, but due to its radioactivity has been replaced by lanthanum oxide in modern eye glasses. Large amounts of iron are used in glass that absorbs infrared energy, such as heat absorbing filters for movie projectors, while cerium(IV) oxide can be used for glass that absorbs UV wavelengths.

Another common glass ingredient is "cullet" (recycled glass). The recycled glass saves on raw materials and energy. However, impurities in the cullet can lead to product and equipment failure.

Oldest mouth-blown window-glass in Sweden (Kosta Glasbruk, Småland, 1742). In the middle is the mark from the glass blower's pipe.

Quartz sand (silica) as main raw material

for commercial glass production

Finally, fining agents such as sodium sulfate, sodium chloride, or antimony oxide are added to reduce the bubble content in the glass.[8] Glass batch calculation is the method by which the correct raw material mixture is determined to achieve the desired glass composition.

Glass production comprehends two types of glass:

1- sheet glass, made by the float glass process 2- glass-container glass.

Glass container production

Glass container factories

Broadly, modern glass container factories are three-part operations: the batch house, the hot end, and the cold end. The batch house handles the raw materials; the hot end handles the manufacture proper — the furnaces, annealing ovens, and forming machines; and the cold end handles the product-inspection and -packaging equipment

Hot end

The following table lists common viscosity fixpoints, applicable to large-scale glass production and experimental glass melting in the laboratory:

log10(η, Pa·s)

log10(η, P)

Description

1 2 Melting Point (glass melt homogenization and fining) 3 4 Working Point (pressing, blowing, gob forming) 4 5 Flow Point 6.6 7.6 Littleton Softening Point (Glass deforms visibly under its own

weight. Standard procedures ASTM C338, ISO 7884-3) 8-10 9-11 Dilatometric Softing Point, Td, depending on load 10.5 11.5 Deformation Point (Glass deforms under its own weight on the μm-

scale within a few hours.) 11-12.3 12-13.3 Glass Transition Temperature, Tg 12 13 Annealing Point (Stress is relieved within several minutes.) 13.5 14.5 Strain Point (Stress is relieved within several hours.)

Furnace

The hot end of a glassworks is where the molten glass is formed into Glass Products; beginning when the batch is fed into the furnace at a slow, controlled rate. The furnaces are natural gas- or fuel oil-fired, and operate at temperatures up to 1575°C. The temperature is limited only by the quality of the furnace’s superstructure material and by the glass composition.

Froming Process

There are, currently, two primary methods of making a glass container — the blow and blow method and the press and blow method. In both cases a stream of molten glass, at its plastic temperature (1050°C-1200°C), is cut with a shearing blade to form a cylinder of glass, called a gob. Both processes start with

the gob falling, by gravity, and guided, through troughs and chutes, into the blank moulds. In the blow and blow process, the glass is first blown from below, into the blank moulds, to create a parison, or pre-container. The parison is then flipped over into a final mould, where a final blow blows the glass out, in to the mould, to make the final container shape. In the case of press and blow process, the parison is formed with a metal plunger, which pushes the glass out, into the blank mould. The process then continues as before, with the parison being transferred to the mould, and the glass being blown out into the mould.

Blow-blow-process (on IS machine)

Form of parison and finished bottle - blow-

blow

dito, press-blow (narrow neck)

Forming machines

The forming machines hold and move the parts that form the container. Generally powered by

compressed air, the mechanisms are timed to coordinate the

movement of all these parts so that containers are made.

The most widely used forming machine arrangement is

the individual section machine (or IS machine). This machine

has a bank of 5-20 identical sections, each of which contains

one complete set of mechanisms to make containers. The

sections are in a row, and the gobs feed into each section via a

moving chute, called the gob distributor. Sections make either one, two, three or four containers

simultaneously. (Referred to as single, double, triple and quad gob). In the case of multiple gobs,

the shears cut the gobs simultaneously, and they fall into the blank moulds in parallel.

Internal treatment

After the forming process, some containers—particularly those intended for alcoholic spirits—undergo a treatment to improve the chemical resistance of the inside, called internal treatment or dealkalization. This is usually accomplished through the injection of a sulfur- or fluorine-containing gas mixture into bottles at high temperatures. The gas is typically delivered to the container either in the air used in the forming process (that is, during the final blow of the container), or through a nozzle directing a stream of the gas into the mouth of the bottle after forming. The treatment renders the container more resistant to alkali extraction, which can cause increases in product pH, and in some cases container degradation.

Annealing

As glass cools it shrinks and solidifies. Uneven cooling causes weak glass due to stress. Even cooling is achieved by annealing. An annealing oven (known in the industry as a Lehr) heats the container to about 580°C then cools it, depending on the glass thickness, over a 20 – 6000 minute period.

Cold end

The role of the cold end is to inspect the containers for defects, package the containers for shipment and label the containers.

Inspection equipment

Glass containers are 100% inspected; automatic machines, or sometimes persons, inspect every container for a variety of faults. Typical faults include small cracks in the glass called checks and foreign inclusions called stones which are pieces of the refractory brick lining of the melting furnace that break off and fall into the pool of molten glass which subsequently are included in the final product. These are especially important to select out due to the fact that they can impart a destructive element to the final glass product. For example, since these materials can withstand large amounts of themal energy, they can cause the glass product to sustain thermal shock resulting in explosive destruction when heated. Other defects include bubbles in the glass called blisters and excessively thin walls. Another defect common in glass manufacturing is referred to as a tear. In the press and blow forming, if a plunger and mould are out of alignment, or heated to an incorrect temperature, the glass will stick to either item and become torn. In addition to rejecting faulty containers, inspection equipment gathers statistical information and relays it to the forming machine operators in the hot end. Computer systems collect fault information to the mould that produced the container. This is done by reading the mould number on the container, which is encoded (as a numeral, or a binary code of dots) on the container by the mould that made it. Operators carry out a range of checks manually on samples of containers, usually visual and dimensional checks.

Secondary processing

Sometimes container factories will offer services such as labelling. Several labelling technologies are available. Unique to glass is the Applied Ceramic Labelling process (ACL). This is screen-printing of the decoration onto the container with a vitreous enamel paint, which is then baked on. An example of this is the original Coca-Cola bottle. The Absolut Bottles have various added services such as: Etching ( Absolut Citron/) Coating (Absolut Raspberry/Ruby Red)and Applied Ceramic Labelling ( Absolut Blue/Pears/Red/Black)

Packaging

Glass containers are packaged in various ways. Popular in Europe are bulk pallets with between 1000 and 4000 containers each. This is carried out by automatic machines (palletisers) which arrange and stack containers separated by layer sheets. Other possibilities include boxes and even hand sewn sacks. Once packed the new "stock units" are labelled and warehoused.

Coatings

Glass containers typically receive two surface coatings, one at the hot end, just before annealing and one at the cold end just after annealing. At the hot end a very thin layer of tin oxide is applied either using a safe organic compound or inorganic stannic chloride. Tin based systems are not the only ones used, although the most popular. Titanium tetrachloride or organo titanates can also be used. In all cases the coating renders the surface of the glass more adhesive to the cold end coating. At the cold end a layer of typically, polyethylene wax, is applied via a water based emulsion. This makes the glass slippery, protecting it from scratching and stopping containers from sticking together when they are moved on a conveyor. The resultant invisible combined coating gives a virtually unscratchable surface to the glass. Due to reduction of in-service surface damage the coatings often are described as strengtheners, however a more correct definition might be strength retaining coatings.

Ancillary processes – compressors & cooling

Forming machines are largely powered by compressed air and a typical glass works will have several large compressors (totaling 30k-60k cfm) to provide the needed compressed air. Furnaces, compressors and forming machine generate quantities of waste heat which is generally cooled by water. Hot glass which is not used in the forming machine is diverted and this diverted glass (called cullet) is generally cooled by water, and sometime even processed and crushed in a water bath arrangement. Often cooling requirements are shared over banks of cooling towers arranged to allow for backup during maintenance.

Marketing

Glass container manufacture in the developed world is a mature market business. Annual growth in total industry sales generally follows population growth. Glass container manufacture is also a geographical business; the product is heavy and large in volume, and the major raw materials (sand, soda ash and limestone) are generally readily available, therefore production facilities need to be located close to their markets. A typical glass furnace holds hundreds of tonnes of molten glass, and so it is simply not practical to shut it down every night, or in fact in any period short of a month. Factories therefore run 24 hours a day 7 days a week. This means that there is little opportunity to either increase or decrease production rates by more than a few percent. New furnaces and forming machines cost tens of millions of dollars and require at least 18 months of planning. Given this fact, and the fact that there are usually more products than machine lines means that

products are sold from stock. The marketing/production challenge is therefore to be able to predict demand both in the short 4-12 week term and over the 24-48 month long term. Factories are generally sized to service the requirements of a city; in developed countries there is usually a factory per 1-2 million people. A typical factory will produce 1-3 million containers a day. Despite its positioning as a mature market product, glass does enjoy a high level of consumer acceptance and is perceived as a “premium” quality packaging format.

Lifecycle impact

Glass containers are wholly recyclable and the industry in many countries retains a policy (or is forced to by Government) of maintaining a high price on cullet to ensure high return rates. Return rates of 95% are not uncommon in the Nordic countries (Sweden, Norway, Denmark and Finland). Return rates of less than 50% are usual in other countries. Of course glass containers can also be reused, and in developing countries this is common, however the environmental impact of washing the container as against remelting them is uncertain. Factors to consider here are the chemicals and fresh water used in the washing, and the fact that a single use container can be made much lighter, using less than half the glass (and therefore energy content) of a multiuse container. Also, a significant factor in the developed world's consideration of reuse are producer concerns over the risk and consequential product liability of using a component (the reused container) of unknown and unqualified safety. How glass containers compare to other packaging types (plastic, cardboard, aluminium) is hard to say, conclusive lifecycle studies are yet to be produced.

Colored / Stained glass The term stained glass can refer to coloured glass as a material or to works made from it. Throughout its thousand-year history, the term has been applied almost exclusively to the windows of churches and other significant buildings. Although traditionally made in flat panels and used as windows, the creations of modern stained glass artists also include three-dimensional structures and sculpture.

Modern vernacular usage has often extended the term "stained glass" to include domestic leadlight and objets d'art created from lead came and copper foil glasswork exemplified in the famous lamps of Louis Comfort Tiffany.

As a material stained glass is glass that has been coloured by adding metallic salts during its manufacture. The coloured glass is crafted into stained glass windows in which small pieces of glass are arranged to form patterns or pictures, held together (traditionally) by strips of lead and supported by a rigid frame. Painted details and yellow stain are often used to enhance the design. The term stained glass is also applied to windows in which the colours have been painted onto the glass and then fused to the glass in a kiln.

Stained glass, as an art and a craft, requires the artistic skill to conceive an appropriate and workable design, and the engineering skills to assemble the piece. A window must fit snugly into the space for which it is made, must resist wind and rain, and also, especially in the larger windows, must support its own weight. Many large windows have withstood the test of time and remained substantially intact since the late Middle Ages. In Western Europe they constitute the major form of pictorial art to have survived. In this context, the purpose of a stained glass window is not to allow those within a building to see the world outside or even primarily to admit light but rather to control it. For this reason stained glass windows have been described as 'illuminated wall decorations'.

The design of a window may be non-figurative or figurative; may incorporate narratives drawn from the Bible, history, or literature; may represent saints or patrons, or use

A large Perpendicular style Gothic window of eight lights in Canterbury Cathedral, c.

1400, which contains medieval glass.

symbolic motifs, in particular armorial. Windows within a building may be thematic, for example: within a church - episodes from the life of Christ; within a parliament building - shields of the constituencies; within a college hall - figures representing the arts and sciences; or within a home - flora, fauna, or landscape.

Colorants

We may devide the materials used to give colours to glass. The first of t hese include there is those materials oxides which seen to be in true solution in the glass if not actually in combination as silicates. The second group includes those few elementary substances who’s coloring effect seem to be due to their presence as particles of colodal size.

As an approach to the discussion of these colorants in particular, we shell select the method of treating each element and its different stages of oxidation separately, and later tabulate for convenience and comparison the effects produced by the various coloring agents. It will be convenient to begin with the colorants of the first group and to consider these in the order of their atomic weights and elements, that is, their atomic number. Curiously, we find the series of the metallic elements of atomic number 23 to 29 inclusive, which apply the most interesting to the glass colorants.

Vanadium:

Vanadium forms two principle oxides, V2O5 and V2O3 the first of these is a basic oxide and gives glass a yellowish green color. It is seldum used as a colorant because of its high cost, and because green can be obtain more cheaply in other ways. The oxide V2 O5 has an acid character, and forms vanadates which are yellow. It seems to be impossible to retain vanadates or V2 O5 in silica glass. But the final result is as always decomposition or reduction to the V2O3 condition which the corresponding green color.

This instability of the higher, acidic oxides of the elements in the silicate glasses deserves the attention it seen to state safe as a general principal that the higher oxides are stable in comparatively basic melts, while the lower basic oxides aer stable when silica is definitely in excess. For example, in fused borax where we have to deal only with the weekly acid B2O5 a vanadate or V2O5 may be dissolved and made to field a characteristics yellow decoration. But the adition to the melt of every small quantity of silica cause the disappearance of the yellow color and the characteristics green of V2O3

Chromium:

Chromium is one of the most powerful of all coloring agents used in the glassmaking industry and is used in the production of dark green glass taking over from the use of iron oxide which had been used to produce this color. The material can be introduced into glass either in the form of chromic oxide or potassium dichromate (K2Cr2O7) , the latter being a more convenient form. This material is

a very powerful colouring agent that excessive use produces a black glass. According to glassmakers we now know that chromium is not easily soluble in glass and chromic oxide may form chromates, which remain in the glass as un-dissolved black specks. It was report that in the St. Helens area of Lancashire, England some railway wagons delivering limestone to the glassworks had previously carried chromium ore and minute quantities of the ore, which had not been swept out, had found their way into the glassworks and ruined many days of production. A costly error, which not only affected production but could have also lead to a lack of confidence in the finished product from the glassworks. Potassium chromate (K2CrO4) is yellow and this colour can be imparted to certain glasses. To produce emerald green glass in which a yellowish cast has to be avoided the addition of tin oxide and arsenic is necessary. The manufacture of chromium aventurine, which nowadays is hardly ever produced, is of historical interest. The aventurine effect is caused by the formation of fairly large plates of chromic oxide, which crystallise out from the melt. During the stage of blowing these crystals orient themselves nearly parallel to the glass surface and it is their reflections, which give a glittering effect to the finished article. Whilst chromium is associated mainly with the production of green glass, other colours from yellow through bluish-red, red to dark green or even black can be achieved in combination with other oxides.

Chromium two oxides of interest to the glass maker interest to the glass maker, CrO3 basic or chromium anhydride and chromium trioxides CrO3 has an arrange red color with water it forms chromium acid. It reacts with the alkalies to form chromate and dichromate, example of which are yellow sedium chromate, Na2CrO4 and arrange sodium dichromate, Na2O7. H2O. in rater basic glazes and enables, it is possible to retain chromate dissolved in such a manner as to yield yellow or orange color. But in the common silica glasses by iron may be any tint between yellow green and greenish blue the reaction.

Cobalt

Cobalt is the most powerful blue colorant used in glassmaking producing rich blues when used in potash containing mixes, but it can also give shades of pink when used in a boro-silicate mix and green when used with iodides. There is no significant evidence as to when cobalt was first used as a colouring agent, but evidence can be seen in stained glass windows going back as far as the twelfth century. Cobalt is not only used in the glassmaking fraternity but was used extensively in the production of blue glazes in the pottery industry. Chinese porcelain, from the Tang Dynasty 616 to 906 and the Ming Dynasty 1368 to 1644, vases were decorated with cobalt blue. The addition of cobalt to the glass mix will produce a blue colour and its intensity depends upon the base glass. The

deepest of blues are produced when used in glass containing potash. Very small quantities are used for physical decolourising, and the amount is so small that it must be added into the batch mix with sand, as the small amount of cobalt, if introduced on its own would have no chance of being uniformly distributed throughout the batch. In this way the sand acts as a pre-mixed dilutant. It is true to say most decolourising agents are used in very small quantities that it is normal to premix with sand to enable a better dispersion throughout the batch.

Cobalt appears in two stages of oxidation, CO.Co2C3 and their compounds, Co3O4 which is the black cobalt oxide of commerce. It yields in all commercial glasses a violet blue color which is so distnative that it has the name “Cobalt Blue”. Cobalt has an amazingly high coloring power. As little as one part is 500,000 produces a recognizable tint and one part is 5000 produces a blue sufficiently intense for most ware. When used in the combination with other colorants such as chromium or cobat, may be made by yield a blue of any desired tint from the pure cobalt itself. Throw this region of the spectrum therefore, the glass maker is in possession of means for the production of the literacy of green and blue. Cobalt is used with manganese and other colorants in the production of black, where its intence coloring power makes it very valuable in spit of its high cost. It is also used as a final corrective in decolorizing.

Copper:

Copper is a very powerful and also a versatile colouring agent when used in colouring glass and its use can be traced back many years. The now famous Egyptian Blue Glass, which was so popular during the time of the Roman Empire, was made using a copper compound. Copper greens and blues are not difficult to produce, although the behaviour of copper in a silicate melt can be complicated. Copper was used most profusely to produce green glass. The art of using copper for ruby glass goes far back to ancient times but even so using copper oxide (CuO) to make ruby glass can be very difficult. Today we find copper being used to produce turquoise blue tones.

Copper forms cuprous oxide, Cu2O, which is red and cuprei oxide CuO, which is black. It produces normaly a greenish blue color intermediate between those chromium and cobalt. Hence it is a valuable coloring agent with those two colouring agents historicaly it is probably one of the oldest of the coloring oxides to be used and it appears in many of ancient Egyptian of glass as well as in the glasses of ancient times. Copper allow this blue colour under neutral or oxidizing agents under strong reduction, this color disappears. It is quite probable that oxides is reduced not to the coopers from but to metallic copper,

which remains dissolved without at first producing any color effect. Then upon reheating the colour “strikes” producing the copper ruby. This is regarded by most authorities as a color produced by colidal particles of metallic copper brought by reheating process into a suitable degree of dispersion to transmit particularly nothing but red light. It is entirely possible that these particles may consist of cooperies oxide whose chemical activity is so low that it easily driven out of compination with the silica by reheating process and made to appear in separate form

Curium:

Curium forms two principle oxides CeO2and Ce2O3. The commercial product is the hydrate of the higher oxide containing usually 75 percent of the rare-earth group obtained by monazite sand as by products in the refining of the oria of mantles used in the glass lamp.

Luria used alone has little or no colouring effect. It was shown by W.E. Taylor that when used with combination with titanium, TiO2. Curiea will produce a very attractive yellow color. The chemistry of this colour formation is somewhat obscure. Perhaps the colourizers from the formation of titanium. The coloring power of the curie titinia combination is rather weak. As much as of three percent of these oxides is required to produce a satisfactory yellow for the tableware. The intensity of the colour is increased by intreasing the titania by keeping the curia constant. This suggest that there may b a partition of ceria between silia and titania which is carried to the titania side with great constraction of the latter. This combination of the colorants is an unused in that such a large proportion of these oxides must be present that there is a read effect as the working effect of the glass conferred by these two refractory.

Neodymium:

Several other rare earth are separable from monazite after the remover of thoria and some of these expert destined coloring action. The only once that seems to have been used commercial aside from ceria is neodymium oxalate containing approximately 50 percent of oxide. Because of its scarecity and the difficulty of separating it completely from praysodium it is at present the most expensive of the coloring oxides. It produces in the glass, when represent in concentration of several percent a beautiful violet color. The neodymium glass is distingtly, blue-violet, unfortunately the high cost of the reagent make this beautiful glass unfortunable of any exept the most expensive line of glassware.

Uranium:

The thought of 19th century glassmakers using Uranium certainly emphasises the risks they undertook to achieve a piece of glass in a colour very desirable, unaware of the properties now associated with the handling of such a mineral. Glasshouses all over the world in the 19th century would surely have set high readings on 'Geiger' counters. Uranium produces a yellow coloured glass (This type of Uranium Glass is termed 'Vaseline Glass' by collectors in the USA), however when used in a very high lead containing glass will produce a deep red colour.

Manganese:

Some of the oldest compounds used in the colouring glass are manganese compounds. Evidence is found in early Egyptian purple glass that manganese is present. Manganese in its low state of oxidation is colourless, but it is a powerful oxidising agent and can be used for decolourising purposes to oxidise the iron content. Glassmakers have over the years substituted manganese by sodium nitrate or selenium in decolourising. Manganese is mainly used in the production of purple glass resembling the colour of potassium permanganate (KMnO4) crystals. The purple colour is achieved by the trivalent manganese however in its divalent state it only imparts a weak yellow or brown colour which are responsible for the green and orange fluorescence of manganese glass.

The element manganese is of particular interest to the glass melt, because it was undoubtedly one one of the first to be used for its coloring effect, and because it was used for hundreds of years as a only satisfactory decolorizer manganese forms a number of oxides of these, we are interested in the dioxide MnO2 (glass makers, “Manganese” or pyrosulite), the sesqiouside, Mn2O3and manganese oxides MnO, we might also mention the heptoxide Mn2O7, not available such as, but as the commercial compound potassium permanganate, KMnO4. The principal regent for the introduction of the manganese is the dioxide. Potassium permananet is sometime used, but the net result per unit of manganese introduced seems to be substantially the same.

Iron :

Iron is a very useful and powerful colouring agent even though it can be an undesirable impurity in making glass. Iron when used in its highest state of oxidation could in combination with barium oxide (BaO) give a reddish-blue glass, but these would have melted under high oxygen pressures and cannot be produced in practice. Iron in its

metallic forms cannot remain in equilibrium with glass and can be disregarded, however its ferrous and ferric forms are of a great help in producing coloured glass. In a reduced condition it can be combined with chromium to produce a deep green glass used in the production of wine bottles. Used with the combination of sulphur (S) , iron sulphides are formed giving a dark amber colour. Used on there own iron and sulphur would not give the amber colour required and a reducing agent such as carbon (C) powder is added to the batch. The shade of amber can only be controlled within narrow limits by varying the amount of coal, which is added in relation to the already existing iron impurity and the carbon matter in the raw materials.

Typical Base Glass For use In Colored Glasses

Type Discription Sand Soda Ash Potash Lime Spar Red Lead Nitr 1 Potash Lime

Silica 1000 -- 275 200 -- 50

2 Soda Lime Silica

1000 325 -- 200 -- 50

3 Potash Lead Silica

1000 -- 275 -- 650 50

Decolonization:

In almost all the raw materials used as batch constituents and in the refractory materials a portion of which is dissolved by the glass, iron oxide is present to a greater or less extend as an impurity. These iron compounds import a characteristic greenish-yellow colour to glass and to counteract this, decolorizing agents are added to the batch.

One method is to oxides the iron to the ferric state, for the yellow color of iron in the ferric state is not a intense and noticeable as the blue color of the some amount of the iron in the ferrous state. Potassium and sodium nitrates are the usual oxidizing agents added for the purpose.

The Batch Composition For The Coloured Glasses

Color Coloring Agents Amount Added to Glass Type Purple NiO 7.5 1 Violet MnO2 400 1 & 3 Black {MnO2 CoO} {200, 50} 2 Blue CoO 15 1 & 2 & 3

Blue- Green CuO 50 2 Aqua marine CuO 50 1 & 3

Green {K2 Cr2 O7, Fe2 O3 , CuO}

{5,1,1.5} 1

Green BaCrO4 30 1 & 3 Green { Na2 U2 O7 .3H2O, CuO}  {35, 1} 3 Opal Ca3 (PO4)2 250 1 & 3 Opal {No3AlF8,  Al2O3 }  Ruby AuCl3 0.4 3 Ruby Se 175 1

Amber { C, S} {6, 5} 2 Amber {Fe2O3 , MnO2} {20, 60}

A second method is to add the complementary purple color to the yellow green iron color to that white light is absorbed uniformly from the visible region. This method gives the best result when bath colors are faint, because the effect has been obtained by subtraction of light with consequent less in brightness. The limit for successful decolorizing is 0.1 per cent Fe2O3. The Complementary Color is obtained by manganese dioxide. Annealing reduces the manganese color so that the ware must enter the Lahr slightly on the pink side. The pind color can be re-developed in sunlight, on effect known as solorization. Hower, in tank melted glass containing salt cake and carbon, the manganese color is destroyed. For these reasons, the use of manganese dioxide as a decolorizing agent is limited to red glass melted in pats where oxidizing conditions prevail.

Selenium and cobalt oxide together produces a more stable complementary color, reducing condition during melting are necessary to develop the selenium pink, consequently its use in mainly in tank furnace. Lead, melted under oxides condition cannot decolorized with selenium only one part of the selenium per 32,000-64,000 parts of sand and about 1/6 of this amount of cobalt oxide are needed to decolorize most glasses.

Opal Glass

These glasses having a light-diffusing crystallite phase and commonly refer ed to as pacified or opal glasses. It is particularly directed to fluoride opal glasses in which the light diffusing crystallite phase is composed primarily of alkali fluorides and “strikes in,” that is develops or separates in the glass, very rapidly, and to the production of incandescent lamp bulbs and similar light transmitting glassware from such glasses

The rate at which opal glasses strike may vary markedly, some glasses developing an opacifying crystallite pase so slowly as to be thermally opacifiable, tha is clear a transparent when initially molded and cooled and requiring a subsequent heat treatment for opal development. However, for commercial production a spontaneously opacifiable glass is desired, that is one which strikes in fully during the cooling cycle incidental to a given molding process. In hand molding and automatic pressing operations at least ten second time, and as much as a minute or more is usually available for striking in the opal phase. Further, such oprations are sufficiently flexile that the process can readily be adapted to a particular glass with no serious consequence other than a slow production rate.

The glasses of the present invention comprise essentially

SiO2 55-75% Al2O3 2-12% Li2O 0.5-3.0% Na2O 6% Alkali metat oxide content 12-20% F 5-9%

Glasses containing one or more of the above consituents in amount appreciably outside the recited ranges are unsuitable for various reasons. Thus an excess of SiO2 or Al2O3, or a deficiency in total alkali metal oxide, produces a glass that is so hard or viscuous as to be too difficult to melt and work. On the other hand, a de-ficiency in SiO2 or Al2O3, or an excess of alkali metal oxide, produces too soft a glass and also one that has poor chemical durability as evidenced by clouding, filming, or other deterioration of the glass surface. This is particularly serious in connecton with lamp envelopes since it interferes with proper sealing of parts, as well as with lamp efficiency.

The presence of F is, of course, essential for development of an opal phase. Also the rate of striking increases markedly with F content. At least 5% is required for theses

purposes, but over about 9% imparts too high a liquidus to the glasses and tends to cause devitrification.

Up to 6% PbO and up to 5% B2O3may be advantageously used to adjust physical properties such as viscosity and expansion coefficient. An excess of PbO tends to unduly soften the glasses while the use of B2O3 is limited by its tendency to volatilize during melting and remove F from the glass.

In further explanation of my invention the following table sets forth, in units by weight, batches from which illustrative glasses may be melted:

1 2 3 4 5 6 7 8 Sio3 668 231 232 214 254 280 270 201 Na2Co3 73.5 39 32 52 39 89 33 20 NaNO3 28 14 7 7 7 14 14 14 K2CO 3 105 27.5 49 14 42 -------- 42 25 Li2CO3 24.5 -------- -------- -------- -------- -------- -------- -------- Lepidolite -------- 114 114 114 114 114 114 57 Al(OH)3 126 -------- -------- -------- -------- -------- -------- -------- Feldspar -------- 68 82 82 27 -------- -------- 167 Na2SiF5 112 44 37 28 37 37 36 43 CaF2 14.5 -------- -------- -------- -------- -------- -------- -------- CaCO3 -------- 9 -------- -------- -------- -------- 9 9 BaCo3 32 16 -------- 38 -------- -------- 18 16 ZnO -------- -------- -------- -------- 18 15 7.5 -------- PbsiO4 -------- -------- -------- -------- 18 18 23 -------- As2O3 4 2 -------- -------- -------- -------- -------- -------- Table II sets forth glass compositions corresponding to, and calculatd in weight percent from, the respective hatches recited in Table II

1 2 3 4 5 6 7 8 SiO2 65.6 66.1 67.2 64.8 64.4 65.9 64.1 65.0 Na2O 8.4 8.5 7.0 8.3 7.1 12.6 7.1 8.0 K2O 6.8 6.8 10.0 5.7 9.1 2.9 7.5 8.0 LI2O3 0.9 0.9 1.0 1.0 1.0 1.0 1.0 0.5 Al2O3 7.7 7.8 8.9 9.3 7.2 6.1 6.2 8.4 BaO 2.3 2.3 -------- 5.9 -------- -------- 2.3 2.3 ZnO -------- -------- -------- -------- 2.8 2.9 1.5 -------- Cao 1.0 1.0 -------- -------- -------- -------- 1.0 1.0 PbO -------- -------- -------- -------- 2.8 2.9 3.7 -------- F 6.9 6.2 5.6 5.0 5.6 5.7 5.6 5.6

Phosphate Opal Glass

Opal glass and method of preparing it, using as batch ingredients the approximate percentages by weight:

SiO2 66.2 B2O3 10 Al2O3 4.5 P2O5 5 CaO 4.5 MgO 0.8 Na2O 12

M2O/P2O5 2-3 M2O/Cao 6-11

P2O5XSiO2 / M2O = 20 to 30

Where M2O is an alkali oxide principally Na2O but capable of containing K2O or Li2O. The Batch is melted at about 1500 Degree C. gobs cut off and molded at 1230 Degree to 1280 degree and molded articles tempered at 700 degree to 720 degree C. the separation of the opalescent phase begins only when the glass is being shaped to final form and has been sufficiently cooled so that the viscosity of the matrix is so high as to prevent the growth of crystalline structure the result is an opal glass having the appearance of perfect verification and greatly increased strength over prior art opal glass

Opal Glass Compositions

According to a preferred mode of combodiment of the invention, the compositing according to the invention comprises the components below within the following weight limits.

SiO2 60-66% Na2O 9-13% K2O 1.5-2.5% CaO 0.4-1.5%

Al2O3 5-6% BaO 2-3% Ce2O 0-0.1% B2O3 10-12% ZnO 0.5-1.5%

F 0-1% P2O3 1.5-3%

A Composition for opalescent glass according to the invention, more particularly intended for an automatic production, may comprise the oxides below within the following weights limits:

SiO2 65.10% Na2O 9.00% K2O 2.02% CaO 1.05%

Al2O3 5.70% BaO 2.65% Ce2O 0.04% B2O3 11.26% ZnO 0.93%

F 0.45% P2O5 1.80%

A composition for opalescent glass according to the invention, intended more particularly for a “semiautomatic” production, comprising manual stages, may include the oxide bellow within the following weight limits:

SiO2 60.80% Na2O 12.4% K2O 2% Cao 1.1%

Al2O3 5.6% BaO 2.7% Ce2O 0.04% B2O3 11.2% ZnO 0.9%

F 0.5% P2O3 2.6%

Tests have been carried out based on different compositions for opalescent glass according to the invention and are reported in the table here in below.

The table shows the glass composition for each of the articles produced as well as the L colorimeter through a wall of the articles, the latter having been cut before han to allow measurement.

No. 1 No. 2 No. 3 No. 4 SiO2 60.99 60,41 60,44 60,13

K2O 2,03 2,01 2,01 2,00 CaO 1,05 1,04 1,04 1,03 Al2O3 5,66 5,61 5,61 5,58 Fe2O3 0,03 0,03 0,03 0,03 BaO 2,65 2,63 2,63 2,31 Ce2O 0,04 0,04 0,04 0,04 B2O3 11,22 11,12 11,12 11,06 ZnO 0,93 0,92 0,92 0,91 F 0,45 0,44 0,44 0,44 P2O3 2,02 2,42 2,74 2,99 L Colorimetry 87,2 66,9 30,6 24,2

To begin with, these tests show that an increase in the P2O3 content leads to a decrease in light transmission. The light transmissions obtained from theses glass compositions according to the invention are completely satisfactory for the contemplated application.

In addition, the hydrolytic resistance for each of these glass types also is satisfactory, in particular for applications such as those of the perfume and cosmetics industries.

I claim.

1. Glass composition which comprises the components below within the following weight llimits

SiO2 60-66% Na2O 9-13% K2O 1.5-2.5% Cao 0.5-1.5%

Al2O3 5-6% BaO 2-3% Ce2O 0-0.1% B2O3 10-12% ZnO 0.5-1.5%

F 0-1% P2O3 1.5-3%

2. Glass compositions according to claim 1. Which comprises the components below:

SiO2 65.10% Na2O 9.00% K2O 2.02

CaO 1.05% Al2O3 5.70% BaO 2.65% Ce2O 0.04% B2O3 11.26% ZnO 0.93%

F 0.45% P2O5 1.80%

3. An Opalescent borosilicate glass composition comprising at least SiO2, CaO, P2O5 and at least one alkali oxide, where in the SiO2 content ranges between 50 and 61%, the alkali oxide content ranges beteen 13 and 15% percent and the caO content ranges between 0.5 and 3% and the P2O5 content ranges between 2.5 and 3%.

Bronze-Smoke Segment Glass

The present glass is relates to new segment glasses used in the fabrication of fused uniform color bifocal and trifocal ophthalmic lenses. More particularly, the present invention relates to lead-barium bronze-smoke colored segment glasses having indices of refraction of 1.6530 to 1.6610 and total luminous transmittances of about 25 percent of a 2 millimeter glass thickness.

The Lead-barium bronze-smoke colored segment glasses of the present invention have indices of refraction, softening points, and thermal expansion characteristics which make them suitable for fusing to the bronze-smoke colored segment and crown glasses.

The segment glasses of the present invention permit fabrication of bifocal or trifocal ophthalmic lenses which exhibit essentially uniform color density and transmittance properties when fused to the bronze-smoke colored segment and crown glasses disclosed in our cop ending applications.

The glasses of the present invention are described by the calculated compositional ranges presented below.

Component

Percent by weight

SiO2 37 to 41 BaO 17 to 21 Na2O 6 to 10 B2O3 1 to 4 K2O 0 to 2 CaO 2 to 5

TiO2 1 to 5 ZrO2 4 to 8 PbO 15.5 to 18 Sb2O3 0 to 2 Al2O3 0.1 to 3.0 Cao 0.001 to 0.077 NiO 0.1 to 0.4

The butch ingredients for two typical segment glasses of the present invention are given in table I below. All ingredients are given in parts by weight

Table I

Batch Ingredient

Part by Weight “A” “B”

Sand 937 963 Barium Carbonate 650 702 Soda Ash 350 362 Boric Acid 124 143 Sodium Nitrate 30 30 Titanium Dioxide 73 102 Zircunium Silicate 262 260 Lead Oxide 435 463 Antimoney Oxide 10 10 Nickel Oxide 7.2 7.55 Cobalt Oxide 0.105 0.112

The calculated glass compositions “A” and “B” are presented in table II. All oxide percentages are in percent by weight.

Table II

Component

Percent by weight “A” “B”

SiO2 30.2 28.1 BaO 19.3 19.5 Na2O 8.3 8.1 B2O3 2.7 3.0 CaO 3.9 3.5 TiO2 2.8 3.7

ZrO3 6.5 6.4 PbO 16.7 17.0 Sb2O3 0.4 0.4 Al2O3 0.1 0.1 CaO 0.0041 0.0041 NiO 0.2756 0.2756

Table III lists some of the significant optical and physical properties of glasses “A” and “B”

Table III

Property Compositions “A”

Compositions “B”

Inder of refraction, Nd 1.6534 1.6603 Softening Point In Degree F 1268 1267 Coefficient of thermal expansion X10-0per oF. between 70oF and 576 oF

5.1 5.1

Percent luminous transmittance for 2mn. Glass thickness.

26.0 25.0

The glasses of the present invention may have indices of refraction between 1.6530 and 1.6610, softening points from 1260 to 1310 oF, and 3.5X10-o per oF. in the temperature ranges from 70 oF to 575 oF.

The softening points is defined by the American society for testing materials as the temperature at which the viscosity of the glass in 107.8 poises.

The segment glasses herein disclosed should be melted under neutral or slightly oxidizing conditions using conventional melting techniques.

Amber Glass

This type of glass relates to amber glass and has particular relation to amber glass of the reduced or carbon-sulfer type.

Centenary to such accepted teachings of the prior art, I have discovered that reduced amber glass of exceptional stability may be produced through an unusually wide range of coloration within the limits of composition set forth below furthermore, I have discovered a most remarkable and novel relation between the alkali content and the silica content with respect to the effect of these constituents upon the stability of color and the coloration of reduced or carbon sulfer amber glass. ( the term “alkali” as used herin means either or any of the following Na2O, K2O, and li2O)

The limits of compositions of my novel glass are approximately as follows.

Percent Silica 70-80 Alkali 10-17.5 CaO 1.3-13 MgO 0-6.5 Al2O3 0.5-5 Iron expressed as Fe2O2 0.02-0.10

Balance selected from the following minor consttuents: BaO, B2O3, S, F2, TiO2, and SrO

The newly discovered relation between alkali and silica referred to above is that these constituents are required to be present within the above approximate limits in such proportions that the percentages of silica by weight minus twice the percentages of alkali by weight equals K, a constant ranging to number from 45-60 inclusive. Stated otherwise, and letting S represent silica and N alkali, then

S—2N=K

K being a constant dependent upon the amounts of coloring agents used and having a value ranging from 45 to 60 inclusive.

Blue Glass

Glass compositions having various colors are used for example, by architects in glazing building normally, the color selected the architect serves several functions. A first function of the color is to make the glass aesthetically pleasing when viewed from the exterior of the building. Aesthetics will determine the acceptability of a desired particular glass color and, in part, the desired intensity of the color, a second function is to reduce the amount of heat absorbed from the exterior of the building to the interior of the building, so that the air conditioning load in the building is reduced . Generally, more color added to glass results in greater heat absorption. In addition, while color may readily be added to glass to serve these functions, that glass when colored still must have an appropriate visible light transmittance value.

The glass of the present invention generally comprises a base soda-lime-silica glass composition having specific colorants in specific quantities therein.

The basic soda-lime-silica glass comprises 68% to 75% by weight SiO2, up to 5% by weight Al2O3, 5% to 15% by weight CaO, up to 10% by weight MgO, with the proviso that CaO+MgO is 6% to 15% by weight of the glass, 10% to 18% by weight Na2O, and up to 5% by weight K2O, with the proviso that Na2O+K2O is 10% to 20% by weight of the glass. Silica forms the glass matrix. Alumina regulates the viscosity of the glass, and prevents devitrification. Calcium oxide, magnesium oxide, sodium oxide, and potassium oxide act as fluxes to reduce the melting temperature of the glass furthermore, the alumina calcium oxide, and magnesium oxide act together to improve the durability of the glass.

Composition Of The Dark Blue Glass

SiO2 63-70% Na2O 18-18% CaO 5—10% K2O 2-5% B2O3 2-6% Al2O3 2-3.5% Cobalt Oxide 0.5-2.5%

Dark Gray Colored Glass

The present glass type relates to a dark gray colored glass having low visible light transmittance, low ultraviolet ray transmittance, low solar radiation transmittance and low excitation purity, which is suitable for a sun roof or rear window glass of an automobile.

A typical neutral gray colored heat absorbing glass containing Fe2O3, Se, CaO, NiO, Cr2O3 etc, is known.

However, nickel is not desirable, since it sometimes forms nickel sulfide in glass. Nickel sulfide.

More preferably, the glass of the present invention comprises coloring components of the following composition, per 100 parts by weight of the matrix component:

Total iron Calculated as Fe2O3

1.0 to 1.4 parts by weight

FeO 0.1 to 0.3 part by weight TiO2 0 to 1.0 part by weight Se 0.0005 to 0.015 part by weight CoO 0.02 to 0.05 part by weight and Cr2O3 0.002 to 0.05 part by weight

Particularly preferably, the glass of the present invention comprises coloring components of the following composition, per 100 parts by weight of the matrix component:

Total iron calculated as Fe2O3

1.0 to 1.35 part by weight

FeO 0.1 to 0.3 part by weight TiO2 0 to 1.0 par by weight Se 0.0005 to 0.015 part by weight CoO 0.021 to 0.05 part by weight Cr2O3 0.002 to 0.05 part by weight

The glass of the present invention can be produced, for example, as follows, although the process for its production is not particularly limited.

Optical Quality Colored glass

This type of glass relates to a phosphate glass rich in alkali and alkaline earth content with a relatively high elongation and a low devitrification tendency, to serve as a base glass for the production of highly selective CuO color-filter glasses. Due to its low viscosity and associated elasticity properties, such a glass system satisfies the demands for a glass system of good optical quality capable of being continuously deformed and passed over a movable band cooling system.

As can be seen from the present type of glass, that the glass is industrially useful in providing a base glass suitable for the large scale production of highly selective copper oxide filter glasses.

A phosphate glass rich in alkali and alkaline earth metal oxides and containing CuO as a coloring component for optical filter glass in the spectral range from 350 nm to 850 nm, consisting essentially of the following synthesis-composition

P2O5 65.00-70.00 SiO2 0.00 to 0.75 B2O3 0.00 to 2.00 Al2O3 2.50 to 6.00 R2O 11.00 to 17.00 BaO 3.00 to 9.50 CeO2 0.45 to 2.00 Cl 0.15 to 0.75 CuO 2.55 to 6.55 F 0.25 to 1.50 Refining Agents 0.10 to 2.00

Neutral Colored Glass Compositions

This invention relates to a neutral colored glass that has a high visible light transmittance, a reduced total solar heat transmittance, and a reduced ultraviolet radiation transmittance. More particularly, this invention relates to a glass composition that utilizes colorants of iron oxide and one or more of the compounds selected from the group of titanium dioxide, vanadium pentoxide, or ceric oxide to produce glass suitable for use in architectural glazing.

A single colorant, selected from the group of titanium dioxide, vanadium pentoxide, and ceric oxide, is added to the glass composition at about 0.1% by weight. Optionally, a combination of compounds selected from the group of colorants may also be added to the glass composition from about 0.1% to about 2.0% by weight. Amounts of the colorants in the above ranges can produce beneficial effects on color purity and UV absorption, respectively, without deteriously

Ultraviolet 300-400 nanometers Visible 400-770 nanometers Total Solar 300-2130 nanometers

The batch materials are conveniently melted together in a conventional glass making furnace, to form a neutral tinted glass composition, which thereafter may be continuously cast onto the molten metal bath in a float glass process.

The composition of soda-lime-silica flat glasses suitable for use in accordance with the present invention typically have the following weight percentage constituents:

SiO2 65-80% Na2O 10-20 CaO 5-15% MgO 0-10% Al2O3 0-5 K2O 0-5 B2O 0-5 B2O3 0-5