At their most basic level diptychs and triptychs are simply flat objects that are arranged or assembled next to each other to form a whole.
The word 'diptych' itself is translated from Ancient Greek to mean 'two fold'. Subsequently, the earliest known examples we have recorded are from the 6th century BC where tablets, usually made of wood, were hinged and covered in wax for use as an early form of textbook by scholars, then were later developed for use, first in Catholic, then Orthodox teachings and ornamentation. Hinges functioned to protect the inside while it was being transported, as diptychs were often taken to help spread the word of Christianity, and ironically as such they became popular within other religions in missionary areas, such as Buddhism. Their main purpose during this time was also for education, performing a similar function to stain glass windows; images weren't purely decorative, they were a vital aid, as the majority of the populace were illiterate and reading the Bible was a privilege reserved for the educated upper class. They often depicted two images that were representative of each other, saints, two decorative lists, or, as we still see today, wedding portraits. Once you add a third panel a diptych becomes a triptych, commonly used to tell a story that has a beginning, middle, and end, such as Easter or the birth of Christ.
Unknown. The Wilton Diptych. 1395-1399, National Gallery, London.
Stepping away from traditional roots, the one overarching theme in creating a diptych is harmony. Now, that by no means requires tranquility, there may be even be discord, just that there is simply a relationship between the two/three that makes a one, that 3 stories make a more meaningful one. This can be thought of in simplistic terms, such as one image split onto multiple panels, a similar palette or composition, or ever increasingly complex ideas such as social or cultural concepts, and montage.
Sebastian, Vijay. Birds on Wire, Tea Plantation. 2020
Both these diptychs are successful in creating harmony in the literal sense. There is a feeling of calm that comes through by focusing on the same subject matter from a different angle or perspective. This technique creates a broadening sense of atmosphere, bringing the viewer closer to the subject and more deepening their involvement with it.
Iona, John. BCV/PCV: Diptych I, June 2020. 2020.
This is a great example of a diptych where cohesion, geometry, and composition combine to create an image that is aesthetically pleasing to the eye simply because of its balance, or 'harmony'. When assembling photographs together you can ignore the rule of thirds for individual images in pursuit of a balance that is formed by the multiple images together, however, if one image is following the rule then often it is best complimented by another that does so as to not 'throw off' the eye.
The layout of a diptych is imperative to how it is read. It is instinctive in humans to look up to down, so horizontal layouts cater to the widest audience. However, western societies read left to right while in the East it is the opposite, so it is important to think of who your main audience is going to be.
Billson, Laurie Xavier. We Used to Blow on Cakes. 2020.
Although not a particularly aesthetic example this diptych cleverly circumvents the problems of left-right, in that it could be read both ways and the affect is the same: the passage of time. We either feel the space between the anticipation of cake and the receiving of it, or the arrival of cake and its disappearance.
A theme often found within diptychs is life and death, Veritas paintings, made popular in Leiden, The Netherlands in the 17th century, are regularly presented as diptychs. Andy Warhol made the famous Marilyn Diptych 4 days after her death.
Warhol, Andy. Marilyn Diptych. 1962, Tate, London.