The phrase "art horizon" refers to the limit or boundary of one's knowledge or awareness in the field of art. Antonyms for this phrase might include "art ignorance," signifying a lack of knowledge or understanding in the arts, "art limit," implying a restricted range of understanding or creativity in art, or "art confinement," suggesting a sense of being limited or boxed in creatively. Other antonyms might include "art mundanity," indicating a lack of inspiration or novelty in art, or "art stagnation," indicating a lack of growth or progress in one's artistic abilities or perspective.