Beauty may be in the eye of the beholder, but there are certain academic principles that can be applied to works of art to make them naturally appealing to the eye.
Proportions, color schemes, shapes and textures that are derived from visual relationships seen in nature have been used to compose all manner of art and the design of images and objects for thousands of years. Da Vinci "Lady with an Ermine,"
An artist can develop the aesthetics of a piece in countless ways to make the work appeal to viewers as, more or less, something beautiful. But I don't believe it is etched in stone anywhere that art must be beautiful to look at.
Consider how ugliness, awkwardness, repulsion, discomfort, and the grotesque might serve to define a work of art.
Certainly, death by crucifixion is not an attractive or appealing idea to many of us. Nonetheless, Western Art-History is full of numerous pictures and sculptures depicting or referencing the crucifixion of Christ.
More generally, works of art have often depicted people, places, things and ideas that are not conventionally seen to be attractive or beautiful. Sometimes a work can present a subject, a color, a suggestive shape, an odor, or a message that is intentionally disturbing, assaulting, terrifying, blasphemous, uneasy, ordinary, or just not beautiful-looking or attractive by conventional standards.
"The Isenheim Altarpiece"
Suffice it to say that not all art would look pleasant when well hung above your sofa, or displayed in a hotel foyer, or mounted atop the Capitol Dome. But, looking deeper than the conventions of "good taste" and "bad taste," consider the extended aspects of art that don't necessarily focus on a pleasant aesthetic design.
"Standing Woman II"