Proportional script and the six pens (al-aqlam al-sitta)

"Proportional script" (al-khatt al-mansub) is the theory by which the shapes of letters are calibrated and controlled through a series of ratios; Maryam Ekhtiar credits it first to the Abbasid vizier and calligrapher Abu Ali Muhammad ibn Muqla (886–940). With Ibn al-Bawwab (d. 1022) and Yaqut al-Musta'simi (d. 1298) he became a model of character and fine penmanship for later generations; the passing of their styles to pupils was the basis of calligraphic study from the tenth century on, showing the weight of the master–pupil bond. ¹

Ibn Muqla built his system on two shapes: a circle whose diameter is the alif, and a rhomboid dot made by one stroke of the reed pen's nib. From these he canonised the six pens: naskh, thuluth, muhaqqaq, rayhan, tawqi' and riqa'. ¹

The six were sometimes presented as complementary pairs of large and small — thuluth–naskh, muhaqqaq–rayhan, tawqi'–riqa' — each suited to a purpose: naskh for ordinary books and small Qur'ans, muhaqqaq and thuluth for large Qur'ans, and thuluth also for objects and buildings. ¹ Rayhan, tawqi' and riqa' served chancery documents, colophons, book covers and carpet pages. ²

Ibn al-Bawwab added an aesthetic dimension; the only extant work in his hand is a small Qur'an copied at Baghdad in 1000–1001 (Chester Beatty Library, Dublin, MS 1431), in a clear, compact naskh. Yaqut refined the system further; Qadi Ahmad credits him with first cutting the nib at an angle, which gave letters refinement and varied line. He trained many, among them Ahmad ibn al-Suhrawardi. ² See also the pens of writing in Ibn al-Nadim.