Glass (काचः)

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Glass (Samskrit: काचः) is a molten mixture of substances such as lime, sand, alkali and metal oxides. It comes in many forms: transparent, opaque, colored and colorless. Glass is a 'supercooled liquid' whose main component is silica. Mention of glass or kaca is profuse in the ancient Indian texts. Ample evidence suggests that glassmaking was widespread in ancient India and the craft achieved a high degree of success.

Introduction

Glass is certainly considered one among earliest man-made excessive generation materials. The manufacturing of glass changed into a first-rate technological improvement within the ancient times. Glass is always made from a mineral (obsidian) and is formed when siliceous materials (such as silica-rich plants and sand) combine with alkali( wood ash). Controlling the temperature of melting, forming, annealing, spotting and hot foiling are the important techniques applied in the preparation of glass.

Technical terms

Archeometric studies reveal that glass gradually evolved through experimentation by early man with various siliceous materials with the help of pyro-technology. In dealing with ancient glass objects, it is necessary to differentiate glass from glaze and faience, which have some common ingredients and present some identical superficial effects, but are not true glass.

• Glass: Glass is a material created by fusing materials like sand, soda, and lime at high temperatures. The chemical name for glass is SILICON DIOXIDE (Si02). Common names for glass are silica, sand, quartz and flint. Silicon dioxide is one of the most common minerals composing the earth and can be easily found in most parts of the world. Glass and glaze are chemically identical but are worked and used differently.
• Glaze: A glaze is a vitreous substance which is applied in thin layers to another substance acting as the core material. Thus glaze is a glassy layer applied to a core or base of some other material.
• Faience: Faience (glazed siliceous ware) has powdered quartz core with an over glaze, which is soda-lime-silica glass, and is isotropic in nature. Faience consists of a lightly sintered core of crushed quartz grains coated with a translucent blue-to-green glaze, both fluxing due to soda.

Glass in Ancient Indian Literature

Mention of glass (kaca काच) and its by-products, most prominently that of beads, occurs in Brahmanas such as Satapatha Brahmana and Buddhist literature Mahavagga, Cullavagga. The use of the word kaca (काच) for glass was common in daily life during the times of Buddha and thereafter found frequently in Sanskrit and Pali literature. In Yajurveda, kaca (काच) is mentioned as one the articles of which ladies ornaments were made by stringing with gold thread. In Satapatha Brahmana kaca may mean glass beads which were used for decorating horses in the ashvamedha yajna.

एवमेतत्पशो स्कन्दति यस्य निक्तस्य लोमानि शीयन्ते यत्काचानावयन्ति लोमान्येवास्य सम्भरन्ति हिरण्मया भवन्ति तस्योक्तं ब्राह्मणमेकशतमेकशतं काचानावयन्ति शतायुर्वै पुरुष आत्मैकशत आयुष्येवात्मन्प्रतितिष्ठति.. (Sata. Brah. 13.2.6.8) evametatpaśo skandati yasya niktasya lomāni śīyante yatkācānāvayanti lomānyevāsya sambharanti hiraṇmayā bhavanti tasyoktaṃ brāhmaṇamekaśatamekaśataṃ kācānāvayanti śatāyurvai puruṣa ātmaikaśata āyuṣyevātmanpratitiṣṭhati..

Taittriya brahmana also states that glass beads of various colors were used to decorate the manes and tails of horses.

यद् वालेषु काचान् आवयन्ति । .... हिरण्ययाः काचा भवन्ति । (Tait. Brah. 3.9.4.4-5) yad vāleṣu kācān āvayanti | .... hiraṇyayāḥ kācā bhavanti |

According to a few scholars the manufacture of glass and colored glass is documented in ancient literature such as Ramayana, Mahabharata and ancient poetic works such as Bana's Kadambari. However, no glass objects have been recovered from Indus valley areas even though ancient Indian literature references are available. Kautilya in his Arthashastra while laying down rules for the Superintendent of the treasury talks about the identification of various kinds of gems and precious stones and mentions a few times about glass; in the context of testing gems to place them in jewelry, in trade and tax payments, robbery and fines.

• शेषाः काच-मणयः ।। ०२.११.३६ ।। (Arth. Shas. 2.11.36) rest are the glass gems.
• क्षेपणः काच-अर्पण-आदीनि ।। ०२.१३.३८ ।। (Arth. Shas. 2.13.38) Kshepana, guna, and kshudra are three kinds of ornamental work. Setting jewels (kácha, glass bead) in gold is termed kshepana.
• Evidence of trade of glass items

Glass (kacha) was differentiated from crystal (sphatika) as early as in the days of Susruta (Chap. 46). Archaeological evidences support the use of glass beads, bangles, jars, tiles etc. made from 6th or 5th century' B.C. onwards. Most of the glass objects were colored. Glass manufacture practiced as an indigenous industry in ancient India is seen in excavations particularly in the south (Arikamedu, Uraiyur). Along with this, the technique of coloring glass also developed. The glass specimens show that the glass makers of ancient India were highly competent in giving different colors and shades to glass objects. In the drama Vasavadatta (6th ceutury A.D.) mention has been made of glass colored like the neck of peacock.

Chemical analysis revealed, just like in the case of pottery, that coloring agents were obtained from the metallic ores. Different chemicals added to them finally led to attribute different shades of colors and glazes to the glass objects. Colored glass was prepared by mixing silicates of soda, lime and appropriate metallic oxides. Copper oxide, iron oxide, manganese oxides were generally used to give colors to the glass articles as for pottery. A special type of glass beads of 350 A.D. to 750 A.D. found at Ahicchatra is of gold foil glass. Layers of gold foils were poured in between two glass layers. All these prove that craftsmen in ancient India were highly skillful in the sophisticated technique of using metallic ores and chemicals as pigments in coloring very high temperature melting media like glass.

Foreign travel accounts like Pliny’s Naturalis Historia (73—77 AD; translated by Bostock and Riley as The Natura1 History of Pliny in 1890), Periplus Maris Erythraei (considered to be earlier than Naturalis Historia; translated by Schoff as Periplus of the Erythrean Sea in 1912) and Geography of Strabo (17—23 AD); translated by Jones and cited in Majumdar 1960: 279, 394) considered Indian glass to be of high quality as it was made of pounded quartz rather than silica. It has long been suggested that this may have been the reason behind the high silica content in ancient Indian glass.

Raw Materials, Coloring Agents

Iron containing minerals such as hematite, copper, cobalt, manganese, aluminum, or lead were used together with silicates in the desired manner and in suitable quantities to produce various types of glass beads, bracelets, tiles and bottles.

Literature mentions the use of reh or sodic soils as the only ingredient necessary to melt glass as used by ancient Indians. Depending on the region, reh is likewise known as usar, kalar, and oos - designating either the efflorescence itself or the sodic-rich soil. Reh is a soil efflorescence containing huge quantities of sodium salts (carbonate, bicarbonate and sulphate) and ranging proportions of calcium and magnesium salts. The furnace used to soften reh glass became advanced indigenously and the related pyrotechniques have been a critical part of historic Indian knowledge.

Archeological Evidence of Glass

Many scholars agree that people of Indus Valley civilization may not know glass making but some scholars have tried to trace the origin of Indian glass to the Harappan civilization on the basis of finding glazed pottery and quartz beads. Harappans made glazed pottery, which is ceramic with a thin layer of glass on the surface (Tite et al. 1983). Though no true glass has been found in India from the Protohistoric periods at Mohenjodaro and Harappa, the second millennium BCE saw its people able to mould and fuse excellent articles of faience and glazing their quartz beads with frit, a material similar to glass. Archeological excavations brought to light many glass objects - beads, bangles, seals and ornamental pieces - from sites such as Hastinapur, Ropar, Alamgirpur, Ahicchatra, Sravasti, Kausambi, Rajghat, Kopia, Ujjain, Maski, Kodapur, Amavarati, Patliputra, Arikamedu, Bellary, Kolhapur etc, among many other places. Some of the earliest objects mainly beads and bangles were brown, black and dark-green in color. Black and brownish colored glass beads found at Hastinapur are mainly of soda-lime-silicate composition with traces of phosphates and potassium, as well as with varying amounts of iron compounds which are responsible for their color. A number of glass beads of different shapes and colors like blue, red, green, amber, orange and black, dark green, ear-reels with a floral design, 'eye-beads', bangles and seals have been found in the Bhir mound at Takshashila (sixth-fourth century BC).

Kopia situated on the bank of river Anoma in Basti, Uttar Pradesh, is the first archeological site where these is ample evidence of glass manufacture established according to carbon dating techniques. Chemical composition of the glass sample from Kopia records: Silica (66.6%), Aluminum Oxide (7%), alkali metal (Na₂O) 21.7%, ferric oxide (1.6%), lime (2.4%), manganese oxide (0%) and traces of titanium, magnesium oxide and dioxide.

About 30 archaeological excavated sites in different regions of India have produced several glass objects in different colors such as green, blue, red, white, orange and some other shades, showing that Indian glassmakers knew the importance of metal oxides or other compounds to impart desired colors to glassware. In certain places, a few tiles and fragmented parts of vessels also have been found. Based on evidence, the knowledge of chemistry as known by ancient Indians included

• Soda is predominant alkali though potash is also present.
• Iron is the main coloring agent; chromium as colorant is also reported from Atranjikhera.
• Limited chemical analysis show they are low in silica
• Annealing is supposed to be have been done.

Types of Ancient Glass

Ethnographic studies show that India had a unique way of making glass. Glassmakers had sufficient expertise in making beads, bracelets, and several other types. Glass products were made using methods such as moulding, folding, bending and double peeling; sometimes a method called wire wrapping was also used to prepare different types of beads. Moulding was one of the basic techniques used in India to prepare glass. Gold glass beads, green and blue glass, agate flasks, bracelets, earrings, eyeballs, etc. were widely used.