Dual, twin, duplicate, pair, twofold…there are many things that came to mind about today’s prompt. In art twins arouse awe, fear, and curiosity in many societies. Jacob and Esau, Horus and Set, Jekyll and Hyde. There are many more examples of pairs who lure us into worlds found through the looking in the glass. The same, yet not the same. Most often thought of in literary terms, but in fact, very prevalent in art.
From 19th century art through post modernism, doubling in art is emphasized in imagery as it explores identity. Often, the split or opposing within the apparent unity of the personality. It challenges the sense of self. (Self and death/self and madness)
Double (doubling) is very significant as an art process and I’ve only touched the tip of the subject. If you’d like to read more, check out Art Brut, or this article, The Art Of Madness from the Paris Review about art collected from assylum patients by Jean DeBuffet.