Diptych. A diptych is any object with two flat plates attached at a hinge. Devices of this form were quite popular in the ancient world, wax tablets being coated with wax on inner faces, for recording notes and for measuring time and direction. In Late Antiquity, ivory diptychs with covers carved in low relief on the outer faces were a significant art-form: the consular diptych was made to celebrate an individual's becoming Roman consul, but some, perhaps including the Poet and Muse diptych at Monza, may have been made for private use. Some of the most important surviving works of the Late Roman Empire are diptychs, of which some dozens survive, preserved in some instances by being reversed and re-used as book covers. The largest surviving Byzantine ivory panel, is a leaf from a diptych in the Justinian court manner of c. 525-50, which features an archangel. From the Middle Ages many panel paintings took the diptych form, as small portable works for personal use; large altarpieces tended to be made in triptych form, with two outer panels that could be closed across the main central representation. They are one type of the multi-panel forms of painting known as polyptychs. Diptych is also often used in reference to films or pieces of literature that form a complementary pair. When taken together, they are viewed as illuminating each other and comprising a distinct work of art from the individual parts. An example is the pair of Alan Ayckbourn plays, House and Garden. It is in this form that the mention of diptychs in early Christian literature is found. The term refers to official lists of the living and departed that are commemorated by the local church. The living would be inscribed on one wing of the diptych, and the departed on the other. The inscribing of a bishop's name in the diptychs means that the local church considers itself to be in communion with him, the removal of a bishop's name would indicate breaking communion with him. The names in the diptychs would be read publicly by the deacon during the Divine Liturgy, and by the priest during the Liturgy of Preparation. Diptychs were also used to inscribe the names of the saints. Although the wax tablets themselves are no longer used, the term is still used in the Eastern Orthodox Church and Eastern Catholic Churches to describe the contents of the diptychs, with all the same connotations. A diptych is also a type of icon whereby two panels are joined together with a hinge, so that they may fold together for protection when travelling, and then be unfolded for veneration when one's destination has been reached. Such diptychs are also called travelling icons. Often the subjects on the two panels will be a matched set, such as Christ and the Theotokos, or the Annunciation, or Saints Peter and Paul. A face was on the inside of each leaf. One leaf formed a vertical sundial, the other a horizontal sundial. The shadow caster, or gnomon was a string between them, and calibrated as to how far they should open, as the angle is critical. Such a sundial can be adjusted to any latitude by tilting it so its gnomon is parallel to the Earth's axis of rotation. A common error states that if both dials show the same time, the instrument is oriented correctly and faces north. A Diptych made as stated as a combined vertical and horizontal sundial with a string gnomon will show the same time on both dials regardless of orientation. This property of self alignment is only true for diptychs historically in the case for a combination of an analemmatic and a vertical sundial. A double dial on a flat plate consisting of a horizontal and an analemmatic dial will also be aligned properly if both dials show the same time. Some diptychs had rough calendars, in the form of pelekinons calibrated to a nodus in the form of a bead or knot on the string. These are accurate to about a week, which was good enough to time planting of crops. The more common form of diptych in Antiquity was like a shallow box. It had two wooden leaves with hollows on the inside edges, filled with wax, and space for a small wooden scriber. This permitted one to take waterproof notes in the wax without wasting money on paper. The wax could be smoothed and reused. The diptych was a common format in Early Netherlandish painting and depicted subjects ranging from secular portraiture to religious personages and stories. Often a portrait and a Madonna and Child had a leaf each. It was especially popular in the 15th and 16th centuries. Painters such as Jan van Eyck, Rogier van der Weyden, Hans Memling and Hugo van der Goes used the form. Some modern artists have used the term in the title of works consisting of two paintings never actually connected, but intended to be hung close together as a pair, such as Andy Warh
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