A cathedral is a Christian church which contains the seat of a bishop, thus serving as the central church of a diocese, conference, or episcopate. The counterpart term for such a church in German is Dom from Latin domus ecclesiae or domus episcopalis, Italian Duomo, Dutch Domkerk, when the church at which an archbishop or metropolitan presides is specifically intended, the term kathedrikos naos is used. In addition, both the Catholic Church and Orthodox churches have formed new dioceses within formerly Protestant lands for converts, consequently, it is not uncommon to find Christians in a single city being served by three or more cathedrals of differing denominations. In the Catholic tradition, the term cathedral correctly applies only to a church houses the seat of the bishop of a diocese. The abbey church of a territorial abbacy serves the same function, the Catholic Church uses the following terms. A pro-cathedral is a parish or other church used temporarily as a cathedral, usually while the cathedral of a diocese is under construction and this designation applies only as long as the temporary use continues. A co-cathedral is a cathedral in a diocese that has two sees. A proto-cathedral is the cathedral of a transferred see.
The cathedral church of a bishop is called the metropolitan cathedral. The term cathedral actually carries no implication as to the size or ornateness of the building, most cathedrals are particularly impressive edifices. The building is now under renovation and restoration for solemn dedication under the title Christ Cathedral in 2018, in the ancient world the chair, on a raised dais, was the distinctive mark of a teacher or rhetor and thus symbolises the bishops role as teacher. A raised throne within a hall was definitive for a Late Antique presiding magistrate. The history of cathedrals starts in the year 313, when the emperor Constantine the Great personally adopted Christianity, in the third century, the phrase ascending the platform, ad pulpitum venire, becomes the standard term for Christian ordination. During the siege of Dura Europos in 256, a complete Christian house church, or domus ecclesiae was entombed in a bank, surviving when excavated. Otherwise the large room had no decoration or distinctive features at all, in 269, soon after Dura fell to the Persian army, a body of clerics assembled a charge sheet against the bishop of Antioch, Paul of Samosata, in the form of an open letter.
Characteristically a Roman magistrate presided from a throne in a large, richly decorated and aisled rectangular hall called a basilica. The earliest of these new basilican cathedrals of which remains are still visible is below the Cathedral of Aquileia on the northern tip of the Adriatic sea. The three halls create a courtyard, in which was originally located a separate baptistery
Christianity is a Abrahamic monotheistic religion based on the life and teachings of Jesus Christ, who serves as the focal point for the religion. It is the worlds largest religion, with over 2.4 billion followers, or 33% of the global population, Christians believe that Jesus is the Son of God and the savior of humanity whose coming as the Messiah was prophesied in the Old Testament. Christian theology is summarized in creeds such as the Apostles Creed and his incarnation, earthly ministry and resurrection are often referred to as the gospel, meaning good news. The term gospel refers to accounts of Jesuss life and teaching, four of which—Matthew, Luke. Christianity is an Abrahamic religion that began as a Second Temple Judaic sect in the mid-1st century, following the Age of Discovery, Christianity spread to the Americas, sub-Saharan Africa, and the rest of the world through missionary work and colonization. Christianity has played a prominent role in the shaping of Western civilization, throughout its history, Christianity has weathered schisms and theological disputes that have resulted in many distinct churches and denominations.
Worldwide, the three largest branches of Christianity are the Catholic Church, the Eastern Orthodox Church, and the denominations of Protestantism. There are many important differences of interpretation and opinion of the Bible, concise doctrinal statements or confessions of religious beliefs are known as creeds. They began as baptismal formulae and were expanded during the Christological controversies of the 4th and 5th centuries to become statements of faith. Many evangelical Protestants reject creeds as definitive statements of faith, even agreeing with some or all of the substance of the creeds. The Baptists have been non-creedal in that they have not sought to establish binding authoritative confessions of faith on one another. Also rejecting creeds are groups with roots in the Restoration Movement, such as the Christian Church, the Evangelical Christian Church in Canada, the Apostles Creed is the most widely accepted statement of the articles of Christian faith. It is used by Presbyterians and Congregationalists and this particular creed was developed between the 2nd and 9th centuries.
Its central doctrines are those of the Trinity and God the Creator, each of the doctrines found in this creed can be traced to statements current in the apostolic period. The creed was used as a summary of Christian doctrine for baptismal candidates in the churches of Rome. Most Christians accept the use of creeds, and subscribe to at least one of the mentioned above. The central tenet of Christianity is the belief in Jesus as the Son of God, Christians believe that Jesus, as the Messiah, was anointed by God as savior of humanity, and hold that Jesus coming was the fulfillment of messianic prophecies of the Old Testament. The Christian concept of the Messiah differs significantly from the contemporary Jewish concept, having become fully human, suffered the pains and temptations of a mortal man, but did not sin
The Balkan Peninsula, or the Balkans, is a peninsula and a cultural area in Eastern and Southeastern Europe with various and disputed borders. The region takes its name from the Balkan Mountains that stretch from the Serbia-Bulgaria border to the Black Sea, the highest point of the Balkans is Mount Musala 2,925 metres in the Rila mountain range. In Turkish, Balkan means a chain of wooded mountains, the name is still preserved in Central Asia with the Balkan Daglary and the Balkan Province of Turkmenistan. A less popular hypothesis regarding its etymology is that it derived from the Persian Balā-Khāna, from Antiquity through the Middle Ages, the Balkan Mountains had been called by the local Thracian name Haemus. According to Greek mythology, the Thracian king Haemus was turned into a mountain by Zeus as a punishment, a reverse name scheme has been suggested. D. Dechev considers that Haemus is derived from a Thracian word *saimon, a third possibility is that Haemus derives from the Greek word haema meaning blood.
The myth relates to a fight between Zeus and the monster/titan Typhon, Zeus injured Typhon with a thunder bolt and Typhons blood fell on the mountains, from which they got their name. The earliest mention of the name appears in an early 14th-century Arab map, the Ottomans first mention it in a document dated from 1565. There has been no other documented usage of the word to refer to the region before that, there is a claim about an earlier Bulgar Turkic origin of the word popular in Bulgaria, however it is only an unscholarly assertion. The word was used by the Ottomans in Rumelia in its meaning of mountain, as in Kod̲j̲a-Balkan, Čatal-Balkan, and Ungurus-Balkani̊. The concept of the Balkans was created by the German geographer August Zeune in 1808, during the 1820s, Balkan became the preferred although not yet exclusive term alongside Haemus among British travelers. Among Russian travelers not so burdened by classical toponymy, Balkan was the preferred term, zeunes goal was to have a geographical parallel term to the Italic and Iberian Peninsula, and seemingly nothing more.
The gradually acquired political connotations are newer and, to a large extent, after the dissolution of Yugoslavia beginning in June 1991, the term Balkans again received a negative meaning, especially in Croatia and Slovenia, even in casual usage. A European Union initiative of 1999 is called the Stability Pact for South Eastern Europe, and its northern boundary is often given as the Danube and Kupa Rivers. The Balkan Peninsula has an area of about 470,000 km2. It is more or less identical to the known as Southeastern Europe. As of 1920 until World War II, Italy included Istria, the current territory of Italy includes only the small area around Trieste inside the Balkan Peninsula. However, the regions of Trieste and Istria are not usually considered part of the Balkans by Italian geographers, the Western Balkans is a neologism coined to describe the countries of ex-Yugoslavia and Albania
Tengrism, known as Tengriism or Tengrianism, is a Central Asian religion characterized by shamanism, totemism, poly- and monotheism and ancestor worship. In Irk Bitig, Tengri is mentioned as Türük Tängrisi, Tengrism has been advocated in intellectual circles of the Turkic nations of Central Asia since the dissolution of the Soviet Union during the 1990s. Still practiced, it is undergoing a revival in Sakha, Tuva. Burkhanism, a movement similar to Tengrism, is concentrated in Altay, Khukh tengri means blue sky in Mongolian, Mongolians still pray to Munkh Khukh Tengri and Mongolia is sometimes poetically called the Land of Eternal Blue Sky by its inhabitants. In modern Turkey, Tengrism is known as the Göktanrı dini, according to Hungarian archaeological research, the religion of the Hungarians until the end of the 10th century was Tengrism. Tengrists view their existence as sustained by the blue sky, the fertile mother-earth spirit. Heaven, spirits of nature and ancestors provide for every need, by living an upright, respectful life, a human will keep his world in balance and perfect his personal.
The Huns of the northern Caucasus reportedly believed in two gods, Tangri Han, considered identical to the Persian Aspandiat and for horses were sacrificed. Tengrism is practised in Sakha, Buryatia and Mongolia in parallel with Tibetan Buddhism and Burkhanism, Kyrgyz means we are forty in the Kyrgyz language, and Kyrgyzstans flag has 40 uniformly-spaced rays. Tengrist Khazars aided Heraclius by reportedly sending 40,000 soldiers during a joint Byzantine-Göktürk operation against the Persians, several Kyrgyz politicians are advocating Tengrism to fill a perceived ideological void. Dastan Sarygulov, secretary of state and former chair of the Kyrgyz state gold-mining company, established the Tengir Ordo, Sarygulov heads a Tengrist society in Bishkek claiming nearly 500,000 followers and an international scientific center of Tengrist studies. Articles on Tengrism have been published in journals in Kyrgyzstan and Kazakhstan. Kazakhstan President Nursultan Nazarbayev and former Kyrgyz president Askar Akayev have called Tengrism the national, natural religion of the Turkic peoples, Turkish worship of Tengri was mocked by the Muslim Turk Mahmud al-Kashgari, who wrote, The infidels - may God destroy them.
It lost importance when the Uighuric kagans proclaimed Manichaeism the state religion in the eighth century, Tengrism played a large role in the religion of the Gok-Turk and Mongol Empires. Genghis Khan and several generations of his followers were Tengrian believers until his descendant, Uzbeg Khan. The original Mongol khans, followers of Tengri, were known for their tolerance of other religions. Möngke Khan, the fourth Great Khan of the Mongol Empire, said, We believe that there is only one God, by whom we live and by whom we die, and for whom we have an upright heart. But as God gives us the different fingers of the hand, a revival of Tengrism has played a role in Central Asian Turkic nationalism since the 1990s
Sofia is the capital and largest city of Bulgaria. The city has a population of 1.26 million, while 1.68 million people live in its metropolitan area, the city is located at the foot of Vitosha Mountain in the western part of the country, within less than 50 kilometres drive from the Serbian border. Its location in the centre of the Balkan peninsula means that it is the midway between the Black Sea and the Adriatic Sea, whereas the Aegean Sea is the closest to it, Sofia has been an area of human habitation since at least 7000 BC. Being Bulgarias primate city, Sofia is a hometown of many of the local universities, cultural institutions. Sofia is one of the top 10 best places for business in the world. Sofia is Europes most affordable capital to visit as of 2013, for the longest time the city possessed a Thracian name, derived from the tribe Serdi, who were either of Thracian, Celtic, or mixed Thracian-Celtic origin. It seems that the first written mention of Serdica was made during his reign, during the Romans civitas Serdenisium was mentioned the brightest city of the Serdi in official inscriptions.
The city was major throughout the past ever since Antiquity, when Roman emperor Constantine the Great referred to it as my Rome, other names given to Sofia, such as Serdonpolis and Triaditza, were mentioned by Byzantine Greek sources or coins. The Slavic name Sredets, which is related to middle and to the citys earliest name, the city was called Atralissa by the Arab traveller Idrisi and Strelisa, Stralitsa or Stralitsion by the Crusaders. The name Sofia comes from the Saint Sofia Church, as opposed to the prevailing Slavic etymology among Bulgarian cities and towns. It is ultimately derived from the Egyptian Kemetic word sbÅ, meaning star, door and wisdom and this was a tradition of collection of wise literature, shared between Mediterranean cultures, which was called sophia in Greek. In these documents the city is called Sofia, but at the time the region and the citys inhabitants are still called Sredecheski. The city became popular to the Ottomans by the name Sofya. In 1879 there was a dispute about what the name of the new Bulgarian capital should be, the citys name is pronounced by Bulgarians with a stress on the o, in contrast with the tendency of foreigners to place the stress on i.
The female given name Sofia is pronounced by Bulgarians with a stress on the i, Sofia has an area of 492 km2, while Sofia City Province has an area of 1344 km2. Sofias development as a significant settlement owes much to its position in the Balkans. It is situated in western Bulgaria, at the foot of the Vitosha mountain, in the Sofia Valley that is surrounded by the Balkan mountains to the north. The valley has an altitude of 550 metres
The Ottonian dynasty was a Saxon dynasty of German monarchs, named after its first Emperor Otto I, but known as the Saxon dynasty after the familys origin in the German stem duchy of Saxony. The family itself is sometimes known as the Liudolfings, after its earliest known member Count Liudolf. The Ottonian rulers were successors of the Carolingian dynasty in East Francia, in the 9th century, the Saxon count Liudolf held large estates on the Leine river west of the Harz mountain range and in the adjacent Eichsfeld territory of Thuringia. His ancestors probably acted as ministeriales in the Saxon stem duchy, Liudolf married Oda, a member of the Frankish House of Billung. About 852 the couple together with Bishop Altfrid of Hildesheim founded Brunshausen Abbey, Liudolf already held the high social position of a Saxon dux, documented by the marriage of his daughter Liutgard with Louis the Younger, son of the Carolingian king Louis the German in 869. Liudolfs sons Bruno and Otto the Illustrious ruled over parts of Saxon Eastphalia, moreover.
He married Hedwiga, a daughter of the Babenberg duke Henry of Franconia, upon Ottos death in 912, his son Henry the Fowler succeeded him as Duke of Saxony. Henry had married Matilda of Ringelheim, a descendant of the legendary Saxon ruler Widukind, while East Francia under the rule of the last Carolingian kings was ravaged by Hungarian invasions, he rose to a primus inter pares among the German dukes. In 933 he led a German army to victory over the Hungarian forces at the Battle of Riade, by succession regulation, he transferred the power to his second son Otto I, who acceded to an undivided heritage. Otto I, Duke of Saxony upon the death of his father in 936, was elected king within a few weeks. He continued the work of unifying all of the German tribes into a single kingdom, through strategic marriages and personal appointments, he installed members of his own family to the kingdoms most important duchies. This, did not prevent his relatives from entering into civil war, Otto was able to suppress their uprisings, in consequence, the various dukes, who had previously been co-equals with the king, were reduced into royal subjects under the kings authority.
His decisive victory over the Magyars at the Battle of Lechfeld in 955 ended the Hungarian invasions of Europe, the defeat of the pagan Magyars earned King Otto the reputation as the savior of Christendom and the epithet the Great. He transformed the Church in Germany into a kind of church and major royal power base to which he donated charity. By 961, Otto had conquered the Kingdom of Italy, which was an inheritance that none wanted, and extended his kingdoms borders to the north, east. In control of much of central and southern Europe, the patronage of Otto and his immediate successors caused a cultural renaissance of the arts. He even reached a settlement with the Byzantine emperor John I Tzimiskes by marrying his son, in 968 he established the Archbishopric of Magdeburg at his long-time residence. Co-ruler with his father since 961 and crowned emperor in 967, by excluding the Bavarian line of Ottonians from the line of succession, he strengthened Imperial authority and secured his own sons succession to the Imperial throne
Nikephoros II Phokas
Nikephoros II Phokas was Byzantine Emperor from 963 to 969. His brilliant military exploits contributed to the resurgence of the Byzantine Empire during the 10th century and his mother, whose name is unknown, was a member of another powerful Anatolian Greek clan, the Maleinoi. Nikephoros joined the army at an early age and he was appointed the military governor of the Anatolikon Theme in 945 under Emperor Constantine VII. When his father was wounded in battle in 953, Nikephoros was promoted to commander on the eastern frontier. In the war with the Abbasid Caliphate under Al-Muti, Nikephoros began with a defeat in 954, from which he recovered in the following years with victories in Syria. From the accession of Emperor Romanos II in 959, Nikephoros and his younger brother Leo were placed in charge of the eastern and western field armies, in 960,27,000 oarsmen and marines were assembled to man a fleet of 308 ships carrying 50,000 troops. At the recommendation of the influential minister Joseph Bringas, Nikephoros was entrusted to lead this expedition against the Saracen Emirate of Crete, after a nine-month siege, Nikephoros stormed Chandax and wrested control of the entire island from the Muslims in 961.
Upon returning to Constantinople, he was denied the honor of a triumph. He soon returned to the east with a large and well-equipped army, in the campaigns of 962–963, he employed a brilliant strategy to conquer the cities of Cilicia and to advance into Syria. There he captured Aleppo, in collusion with his nephew, John Tzimiskes and it was on these campaigns that he earned the sobriquet, The Pale Death of the Saracens. During the capture of Aleppo, the Byzantine army took possession of 390,000 silver dinars,2,000 camels, early in his life Nikephoros had married Stephano. She had died before he rose to fame, and after her death he took an oath of chastity and this would create problems on. On 15 March 963, Emperor Romanos II died unexpectedly at the age of twenty-six of uncertain cause, Theophano had already gained a reputation as an intelligent and ambitious woman. She would gain a reputation for ruthlessness in achieving her goals, Romanos had already crowned as co-emperors his two sons Basil II and Constantine VIII.
At the time that Romanos died, Basil was five years old, Theophano was not allowed to rule alone. Joseph Bringas, the eunuch palace official who had become Romanos chief councilor, according to contemporary sources he intended to keep authority in his own hands. He tried to reduce the power of Nikephoros Phokas, the victorious general had been accepted as the actual commander of the army and maintained his strong connections to the aristocracy. Joseph was afraid that Nikephoros could claim the throne with the support of both the army and the aristocracy, josephs intrigues during the following months turned both Theophano and Nikephoros against him
Slavs are the largest Indo-European ethno-linguistic group in Europe. They are native to Central Europe, Eastern Europe, Southeastern Europe, Northeastern Europe, North Asia, Slavs speak Slavic languages of the Balto-Slavic language group. From the early 6th century they spread to inhabit most of Central, states with Slavic languages comprise over 50% of the territory of Europe, therefore it is the largest ethno-linguistic group in Europe by land area. Present-day Slavic people are classified into West Slavs, East Slavs, there are an estimated 360 million Slavs worldwide. The Slavic autonym is reconstructed in Proto-Slavic as *Slověninъ, plural *Slověne, the oldest documents written in Old Church Slavonic and dating from the 9th century attest the autonym as Slověne. The word slovo and the related slava and slukh originate from the Proto-Indo-European root *ḱlew-, cognate with Ancient Greek κλῆς, whence comes the name Pericles, Latin clueo, some other theories have limited support. The English term slave eventually derives from the ethnonym Slav, Slavs were captured and enslaved by the Muslims of Spain during the ninth century AD.
The Slavs under name of the Antes and the Sclaveni make their first appearance in Byzantine records in the early 6th century. Procopius wrote in 545 that the Sclaveni and the Antae actually had a name in the remote past. He described them as barbarians, who lived under democracy, and that believe in one god. They lived in scattered housing, and constantly changed settlement, regarding warfare, they were mainly foot soldiers with small shields and battleaxes, lightly clothed, some entering battle naked with only their genitals covered. And they live a life, giving no heed to bodily comforts. Jordanes described the Sclaveni having swamps and forests for their cities, another 6th-century source refers to them living among nearly impenetrable forests, rivers and marshes. Menander Protector mentions a Daurentius that slew an Avar envoy of Khagan Bayan I. The Avars asked the Slavs to accept the suzerainty of the Avars, he declined and is reported as saying, Others do not conquer our land. The relationship between the Slavs and a called the Veneti east of the River Vistula in the Roman period is uncertain.
The name may refer both to Balts and Slavs, perhaps some Slavs migrated with the movement of the Vandals to Iberia and north Africa. Around the 6th century, Slavs appeared on Byzantine borders in great numbers, the Byzantine records note that grass would not regrow in places where the Slavs had marched through, so great were their numbers
Great Basilica, Pliska
The Great Basilica of Pliska is an architectural complex in Pliska, the first capital of the First Bulgarian Empire, which includes a cathedral, an archbishops palace and a monastery. According to the Shumen architectural museums research, an early Christian martyrium that included a cross-shaped church, the martyr buried there is thought to be Enravota, the first Bulgarian saint. The martyrium is thought to have destroyed in 865 during the failed rebellion of the heathens in the wake of the Christianization of Bulgaria. Other researchers, regard the cross-shaped remains as a mausoleum of early Bulgarian rulers, the archbishops residence lay to the north and south of the basilica, the northern yard hosted a residential building, with a bath with a hypocaust lay to the west of it. The building to the south of the cathedral accommodated a school, the yard north of the basilica accommodated monastical buildings with a kitchen and a dining room. The eastern part of the yard was allocated for a building with ten identical monastical cells.
Another bath with a hypocaust, a one, and a well lay in the centre of that yard. Мавзолeят в Плиска — енигмата на старата столица, Кръстовидната сграда под Голямата базилика в Плиска
A nomad is a member of a community of people who live in different locations, moving from one place to another. Among the various ways nomads relate to their environment, one can distinguish the hunter-gatherer, as of 1995, there were an estimated 30–40 million nomads in the world. Nomadic hunting and gathering, following seasonally available wild plants and game, is by far the oldest human subsistence method, pastoralists raise herds, driving them, or moving with them, in patterns that normally avoid depleting pastures beyond their ability to recover. Nomadism is a lifestyle adapted to regions such as steppe, tundra, or ice and sand. For example, many groups in the tundra are reindeer herders and are semi-nomadic and these nomads sometimes adapt the use of high technology such as solar photovoltaics to reduce their dependence on diesel fuel. These groups are known as peripatetic nomads, a nomad is a person with no settled home, moving from place to place as a way of obtaining food, finding pasture for livestock, or otherwise making a living.
The word Nomad comes from a Greek word that one who wanders for pasture. Most nomadic groups follow an annual or seasonal pattern of movements and settlements. Nomadic peoples traditionally travel by animal or canoe or on foot, some nomads travel by motor vehicle. Most nomads live in tents or other portable shelters, Nomads keep moving for different reasons. Nomadic foragers move in search of game, edible plants, the Australian Aborigines, Negritos of Southeast Asia, and San of Africa, for example, traditionally move from camp to camp to hunt and to gather wild plants. Some tribes of the Americas followed this way of life, Pastoral nomads make their living raising livestock, such as camels, goats, sheep, or yaks. These nomads travel to find more camels and sheep through the deserts of Arabia, the Fulani and their cattle travel through the grasslands of Niger in western Africa. Some nomadic peoples, especially herders, may move to raid settled communities or avoid enemies. Nomadic craftworkers and merchants travel to find and serve customers and they include the Lohar blacksmiths of India, the Romani traders, and the Irish Travellers.
Most nomads travel in groups of families called bands or tribes and these groups are based on kinship and marriage ties or on formal agreements of cooperation. A council of adult males makes most of the decisions, though some tribes have chiefs, in the case of Mongolian nomads, a family moves twice a year. These two movements would generally occur during the summer and winter, the winter location is usually located near mountains in a valley and most families already have their fixed winter locations
Pastoralism is the branch of agriculture concerned with the raising of livestock. It is animal husbandry, the care and use of such as camels, cattle, llamas. Pastoralism generally has an aspect, moving the herds in search of fresh pasture. Pastoralism is a strategy to support a population on less productive land. For example, in savannas and their animals gather when rain water is abundant, pastoralists often use their herds to affect their environment. Grazing herds on savannas can ensure the biodiversity of the savannas, pastoralists may use fire to make ecosystems more suitable for their food animals. For instance, the Turkana people of northwest Kenya use fire to prevent the invasion of the savanna by woody plant species, biomass of the domesticated and wild animals was increased by a higher quality of grass. Pastoralism is found in many variations throughout the world, composition of herds, management practices, social organization and all other aspects of pastoralism vary between areas and between social groups.
Many traditional practices have had to adapt to the circumstance of the modern world. Ranches of the United States and sheep stations and cattle stations of Australia are seen by some as modern variations, one theory is that pastoralism was created from mixed farming. Bates and Lees proposed that it was the incorporation of irrigation into farming which ensued in specialization, advantages of mixed farming include reducing risk of failure, spreading labour, and re-utilizing resources. The increased productivity of agriculture led to an increase in population. Bordering areas of land remained in use for animal breeding and this meant that large distances had to be covered by herds to collect sufficient forage. Specialization occurred as a result of the importance of both intensive agriculture and pastoralism. Both agriculture and pastoralism developed alongside other, with continuous interactions. There is another theory that suggests pastoralism evolved from hunting and gathering, hunters of wild goats and sheep were knowledgeable about herd mobility and the needs of the animals.
Such hunters were mobile and followed the herds on their seasonal rounds, undomesticated herds were chosen to become more controllable for the proto-pastoralist nomadic hunter and gatherer groups by taming and domesticating them. Hunter-gatherers strategies in the past have been diverse and contingent upon the local environment conditions
Glass is a non-crystalline amorphous solid that is often transparent and has widespread practical and decorative usage in, for example, window panes and optoelectronics. The most familiar, and historically the oldest, types of glass are silicate glasses based on the chemical compound silica, the primary constituent of sand. The term glass, in usage, is often used to refer only to this type of material. Many applications of silicate glasses derive from their optical transparency, giving rise to their use as window panes. Glass can be coloured by adding metallic salts, and can be painted and printed with vitreous enamels and these qualities have led to the extensive use of glass in the manufacture of art objects and in particular, stained glass windows. Although brittle, silicate glass is extremely durable, and many examples of glass fragments exist from early glass-making cultures, because glass can be formed or moulded into any shape, it has been traditionally used for vessels, vases, bottles and drinking glasses.
In its most solid forms it has used for paperweights, marbles. Some objects historically were so commonly made of glass that they are simply called by the name of the material, such as drinking glasses. Porcelains and many polymer thermoplastics familiar from everyday use are glasses and these sorts of glasses can be made of quite different kinds of materials than silica, metallic alloys, ionic melts, aqueous solutions, molecular liquids, and polymers. For many applications, like glass bottles or eyewear, polymer glasses are a lighter alternative than traditional glass, silica is a common fundamental constituent of glass. In nature, vitrification of quartz occurs when lightning strikes sand, forming hollow, fused quartz is a glass made from chemically-pure SiO2. It has excellent resistance to shock, being able to survive immersion in water while red hot. However, its high melting-temperature and viscosity make it difficult to work with, other substances are added to simplify processing. One is sodium carbonate, which lowers the transition temperature.
The soda makes the glass water-soluble, which is undesirable, so lime, some magnesium oxide. 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 contains other ingredients to change its properties, lead glass or flint glass is more brilliant because the increased refractive index causes noticeably more specular reflection and increased optical dispersion. Adding barium increases the refractive index, iron can be incorporated into glass to absorb infrared energy, for example in heat absorbing filters for movie projectors, while cerium oxide can be used for glass that absorbs UV wavelengths