mix of colors, the size of the furmah, and the complexity and size of interspacing elements such as strapping, braids, or "lanterns." And then there are all the non-star patterns— honeycombs, webs, steps and shoulders, and checkerboards. Islamic decoration and craftsmanship had a significant influence on Western art when Venetian merchants brought goods of many types back to Italy from the 14th century onwards. The tessellations of zellij tilework in the Alhambra of Granada were also an important source of inspiration for the work of 20th-century Dutch artist M. C. Escher. The tessellations in the mosaics are currently of interest in academic research in the mathematics of art. These studies require expertise not only in the fields of mathematics, art and art history, but also of computer science, computer modelling and software engineering. Clays In Morocco, Fez is still a production center for zellīj tiles due in part to the Miocene grey clay found in the area. The clay from this region is primarily composed of kaolinite. In Fez and in other sites including Meknes, Safi, and Salé, the composition of clay used for ceramics is 27–56% clay minerals, of which 3–29% is calcite (around 16% for Fez). Quartz and muscovite are also present, at around 15–29% and 5–18%, respectively. A study by Meriam El Ouahabi, L. Daoudi, and Nathalie Fagel states that: Zellij craftsmen Zellīj making is considered an art in itself. The art is transmitted from generation to generation by ma'alems (master craftsmen). A long training is required to implant the required skills and training usually starts at childhood. In Fez, craftsmen begin training between the ages of 6 and 14 and the average apprenticeship lasts approximately ten years, with many more years required to achieve the status of ma'alem. In 1993, the Moroccan government ratified the Convention on the Rights of the Child (CRC), abolishing the practice of employing children under 15 in work that is hazardous or impedes their education, but a 2019 study reports that the practice of training children has continued. Now young people learn zellīj making at one of the 58 artisan schools in Morocco. However, the interest in learning the craft is dropping. As of 2018, at an artisan school in Fez with 400 enrolled students only 7 students learn how to make zellīj. See also Notes References Further reading at-Tanwīr wa-Diwān at-Tahbīr fi Fan at-Tastīr () by Khalid Saib (in Arabic)