Once a uniquely form of Islamic art emerged, one of its most defining characteristics was surfaces that were completely covered in decoration. There are four different types of decorations found in Islamic art: "calligraphy, vegetal patterns, geometric patterns, and figural representation" (The Metropolitan Museum of Art, Heilbrunn Timeline of Art History, "The Nature of Islamic Art").
Calligraphy is essentially a form of beautiful, embellished writing. Writing became essential to the Islamic culture because the Prophet Muhammed's revelations eventually needed to be recorded in what became called the Koran. Plus, most Muslims could not read; therefore, decorative writing became essential in making the words of the prophet meaningful to all (Heilbrunn Timeline of Art History, "Caligraphy in Islamic Art"). While many cultures use calligraphy as a form of art, Islamic calligraphy became unique due to the fact that Muslims used it more extensively than other cultures and developed it in "astonishingly varied and imaginative ways" (Victoria and Albert Museum, "Calligraphy in Islamic Art").
Vegetal patterns are patterns in which the shapes and images of plants are reflected. Muslims found vegetal patterns attractive due to their strong representation of life surrounding humans although vegetal patterns themselves usually have no symbolic meaning (Islamic Culture Musuem, Hogshead Wold Literature Corportation, "Vegetal Patterns"). In Islamic works of art, we will often find vegetal patterns used in combination with other decorative forms, such as calligraphy or geometric patterns.
Geometic patterns are patterns related to the mathematics of geometry. Across ages and cultures, geometry has been used to represent and unify the world as we see it. Hence, Muslims used geometry, especially circles, in their art to represent this unity.
Figural representation refers to images of any live beings, such as human beings or animals. However, figurative representation was at first not used in Islamic art due to the fact that Muslims believed creating living beings was something only God could do and, therefore, capturing those beings in representation was akin to idolatry. Regardless, as Islam progressed into Arabia, a culture that used figural representation in its own art, figures began appearing more and more in Islamic art (Heilbrunn Timeline of Art History, "Figural Representation in Islamic Art").