Islamic glass
Islamic glass is glass made in the Islamic world, especially in periods up to the 19th century. It built on pre-Islamic cultures in the Middle East, especially ancient Egyptian, Persian and Roman glass, and developed distinct styles, characterized by the introduction of new techniques and the reinterpreting of old traditions. It came under European influence by the end of the Middle Ages, with imports of Venetian glass documented by the late 15th century.
It rarely has religious content, other than inscriptions, although the mosque lamp was mainly used in religious contexts, to light mosques, but it uses the decorative styles of Islamic art from the same times and places. The makers were not necessarily Muslims themselves.
Though most glass was simple, and presumably cheap, finely formed and decorated pieces were expensive products, and often highly decorated, using several different techniques. Muhammad disapproved of the use of tableware and drinking vessels made from precious metals, which remained usual for Christian elites in Europe and the Byzantine Empire. Islamic pottery and glass benefited from this, developing luxury styles in the absence of as much competition from ware in other materials, though some Islamic pottery reached the standards required for court entertainments.
The most important centres were Persia, Egypt, Mesopotamia and Syria through most of the period, with Turkey and India later joining them.
Roman and Sassanian influences
Islamic glass did not begin to develop a recognizable expression until the late 8th or early 9th century AD, despite Islam spreading across the Middle East and North Africa during the mid-7th century AD. Despite bringing enormous religious and socio-political changes to the region, this event appears to have not drastically affected the day-to-day workings of craft industries, nor did it cause "extensive destruction or long-lasting disruption". The Byzantine glass industry and Sassanian glassmaking industries continued in much the same way they had for centuries, and glass was apparently still exported to the Byzantine Empire from the traditional centres, now under Islamic control. Following the unification of the entire region, the interaction of ideas and techniques was facilitated, allowing for the fusion of these two separate traditions with new ideas, ultimately leading to the Islamic glass industry.Roman glassmaking traditions that are important in the Islamic period include the application of glass trails as a surface embellishment, while stylistic techniques adopted from the Sassanian Empire include various styles of glass cutting. This may have developed out of the long-standing hardstone carving traditions in Persia and Mesopotamia. In regards to glass-making technology, tank furnaces used in the Levant to produce slabs of raw glass for export during the Classical Period were used during the Early Islamic Period in the same region until the 10th or 11th centuries AD.
Technological change
During the first centuries of Islamic rule, glassmakers in the Eastern Mediterranean continued to use the Roman recipe consisting of calcium-rich sand and mineral natron from the Wādi el-Natrūn in Egypt, and examples of natron-based Islamic glass have been found in the Levant up to the late 9th century AD. Much Roman glass had apparently begun as enormous slabs made in the Levant, then shipped to Europe for breaking and working. Archaeological evidence has shown that the use of natron ceased, and plant ash became the source of soda for all Islamic glass in the following centuries. The reasons for this technological transition remain unclear, although it has been postulated that civil unrest in Egypt during the early 9th century AD led to a cut-off in the natron supply, thus forcing Islamic glassmakers to look for alternate soda sources.Evidence of experimentation with the basic glass recipe at Beth She'arim during the early 9th century AD further supports this argument. A glass slab made from a tank mould from the site contained an excess amount of lime, and may be the result of mixing sand with plant ash. Although the raw glass would have been unusable due to its composition, it does suggest that at this time, Islamic glassmakers in the Levant were combining aspects of Sassanian and Roman traditions in an effort to solve the problem created by the lack of access to mineral natron. The use of plant ash, specifically from halophytic plants, which were plentiful in the Middle East due to the climate, was well known in Persia and Mesopotamia. It undoubtedly would not take long for the glassmakers in the Near East to correct their manufacturing errors and begin using the plant ash-based recipe used further east.
Early Islamic glass: mid-7th to late 12th century AD
The glass industry in the Early Islamic Period can initially be characterized as a continuation of older traditions, coinciding with the Umayyad Caliphate, the first Islamic dynasty. Following the rise of the Abbasid Caliphate in 750 AD, the capital of the Islamic world was moved from Damascus in the Levant to Baghdad in Mesopotamia. This led to a cultural shift away from the influences of Classical traditions, and allowed for the development of an 'Islamic' expression.The production of glass during this period is concentrated in three main regions of the Islamic world. Firstly, the Eastern Mediterranean remained a centre of glass production, as it had been for centuries. Excavations at Qal'at Sem'an in northern Syria, Tyre in Lebanon, Beth She'arim and Bet Eli'ezer in Israel, and at Fustat in Egypt have all shown evidence for glass production, including numerous vessels, raw glass, and their associated furnaces. In Persia, a formerly Sassanian region, archaeological activity has located a number of sites with large deposits of Early Islamic Glass, including Nishapur, Siraf, and Susa. Numerous kilns suggest Nishapur was an important production centre, and the identification of a local type of glass at Siraf suggests the same for that site.
In Mesopotamia, excavations at Samarra, a temporary capital of the Abbasid Caliphate during the mid-9th century AD, produced a wide range of glass vessels, while work at al-Madā'in and Raqqa provide evidence for glass production in the region. However, it is difficult to clearly identify the place in which a glass piece was manufactured without the presence of wastes, which indicate that the location was a site of glassmaking. Furthermore, during the Abbasid caliphate, both glassmakers and their products moved throughout the empire, leading to dispersion of glassware and "universality of style", which further prevents the identification of a piece's birthplace. As the Seljuk empire arose from Seljuk generals conquering lands under the Abbasid flag only nominally, it is likely that glass technology, style, and trade might have continued similarly under the Seljuks as it did under the Abbasids. Despite the increasing ability and style of Islamic glassmakers during this time, few pieces were signed or dated, making identification of a piece's location of origin unfortunately difficult. Glass pieces are typically dated by stylistic comparisons to other pieces from the era.
The majority of the decorative traditions used in the Early Islamic Period concerned the manipulation of the glass itself, and included trail-application, carving, and mould-blowing. As mentioned previously, glass-carving and trail application are a continuation of older techniques, the former associated with Sassanian glassmaking and the latter with Roman traditions. In relief cutting, a specialized form of glass-carving most often used on colourless and transparent glass, "the area surrounding the decorative elements was carved back to the ground, thus leaving the former in relief".
Unlike relief cutting, trail application, or thread trailing, allowed decoration with hot glass. The glassblower would manipulate molten glass while still malleable and create patterns, handles, or flanges. While cutting reached the height of its popularity from the 9th–11th centuries CE, thread-trailing became more widely used during the 11th–12th centuries, when Seljuq glassmakers were considered at the height of their skill.
Mould-blowing, based on Roman traditions from the 1st century CE, is another specialized technique that spread widely throughout the Islamic Mediterranean world during this period. Two distinct types of moulds are known archaeologically; a two-part mould made up of separate halves, and the 'dip' mould, whereby the viscous glass is placed entirely inside one mould. The moulds were often made of bronze, although there are examples of some being ceramic. Moulds also often included a carved pattern; the finished piece would take on the shape and style of the mould. With these advances in glassmaking technology, artisans began to stylize and simplify their designs, emphasizing designs with "no foreground or background" and "plain but beautiful vessels".
A final decorative technology that is a distinct marker of the Early Islamic Period is the use of painted lustre decoration. While some scholars see this as a purely Islamic invention originating in Fustat, others place the origins of lustre decoration in Roman and Coptic Egypt during the centuries preceding the rise of Islam. Staining glass vessels with copper and silver pigments was known from around the 3rd century AD, although true lustre technology probably began sometime between the 4th and 8th centuries AD. Lustre painting on glass involves the application of copper and silver pigments, followed by a specific firing that allows for the ionic exchange of Ag+ and Cu+ with the glass, resulting in a metallic sheen fully bound to the vessel. Regardless of its specific origins, lustre decoration was a key technology in glass production that continued to develop throughout the Early Islamic Period, and spread not only geographically, but also to other material industries in the form of lustreware glazed ceramics.