When we speak of Turkish calligraphy , we refer to writing of aesthetic value in characters based on the Arabic script , which the Turks had adopted as their writing medium after their conversion to Islam . The Arabic characters gradually assumed an aesthetic function after the advent of Islam , and this process gathered momentum from the mid-eighth century onwards , so that calligraphy was already a significant art discipline by the time the Turks joined the Islamic world . The most succinct definition of calligraphy formulated by Islamic writers is : "Calligraphy is a spiritual geometry produced with material tools." The aesthetic values implied by this definition held true for centuries .