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Ivory consular diptych of Areobindus, Byzantium, 506 AD, Louvre museum

A diptych (pronounced "dip-tick" IPA: [ dip'tik] (or US: [ 'dɪp.tɪk ]) from the Greek δίπτυχο [ ði'pti.xo ] di- "two" + ptychē "fold") is any object with two flat plates attached at a hinge. Devices of this form were quite popular in the ancient world, types existing for recording notes and for measuring time and direction. The term is also used figuratively for a thematically-linked sequence of two books.

In Late Antiquity ivory diptyches with decorated covers were a significant art-form, deriving from the "consular diptych" made to celebrate an individual becoming Roman consul. Many of the most important surviving works of the Late roman Empire are diptychs. From the Middle Ages many panel paintings were in diptych form, from small portable works for personal use to large altarpieces. These are discussed with other multi-panel forms of painting at polyptych.

Traditional diptychs are boxwood, with stamped hour lines and lacquered or varnished finishes. Some were also ivory (superior because it is easiest to read and less prone to wear than wood), or metal (sturdy, harder to read but less expensive than ivory).^[1]

[edit] Writing tablet

Barberini Ivory, Constantinople, 6th century, Louvre.

One form of diptych 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. It was probably excellent for shopping lists or other reminders.

It is in this form that the mention of "diptychs" in early Christian literature is found. The term often 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 (Mass). 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 to describe the contents of the diptychs, with all the same connotations.

[edit] Sundial

Diptych sundial in the form of a mandolin, circa 1612

The other form was a portable sundial. 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 (in the northern hemisphere). 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.^[2] 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.^[3]

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.

[edit] References

[edit] External links

• National Gallery of Art, Prayers and Portraits: Unfolding the Netherlandish Diptych
• Diptych The Catholic Encyclopedia, Volume V, Robert Appleton Company, Online Edition.
• Diptych sundials, National Maritime Museum.