This article studies the metrics and measurements for Arabic (and derived) scripts and compares it with Latin scripts, searching for differences and similarities. In this study, we only focus on two main Islamic calligraphy styles, Naskh (Ar. نسخ) and Nastaliq (Ar. نستعلیق), knowing that almost all other styles follow similar rules.
Historically, Islamic calligraphers used to utilize reed pens for writing—a tradition that has remained until now. A reed pen is carved and cut to make a flat (and usually slanted) nib. Then, the pen is dipped in ink and drawn with different angles and pressures on the paper to create strokes with numerous shapes.
Strokes construct letters and words, thus they need to abide certain rules; some of them originate from the writing system, e.g. shapes of letters and places of dots, and some other are based on aesthetics. Multiple shapes of letters, lots of ligatures and kashidah (lit. stretch) are the most important (unique) features of Arabic calligraphy.
With reed pens in hand, it is natural to express sizes and rules relative to its nib width, however, Islamic calligraphers have found it more useful to measure strokes in terms of nuqta (lit. dot). A nuqta is commonly an oblique square drawn with the whole width of the nib.
Glyphs and Composition
You may have noticed that in Islamic calligraphy, glyphs are too close and sometimes interleaved that in some cases might trouble non-native readers to distinguish words. Also, we observe that some letters are composed of multiple strokes, while some strokes are shared between two or more letters.
In Arabic alphabet, 22 out of 28 letters join to their next letters to form a coherent glyph, as long as they belong to the same word. Thus, when two letters are deliberately disjoint, it is interpreted as a word boundary. This causes Arabic scripts, in contrast to Latin, barely require extra spaces between words.
Similar to Latin, all Arabic glyphs seat on a line called Kursi (or baseline) that is mostly recognized from thick and long horizontal strokes. However, glyphs are very likely to exceed above or below this line.
In addition to the baseline, Latin scripts need three more guidelines: ascender, descender and x-height. Arabic scripts define no such notion, but we can generally assume five guidelines. In the figure below, these guidelines are shown for a Naskh excerpt—with names chosen arbitrarily. Also, the spaces are filled with nuqtas to show the relative measures.
This is almost true for all calligraphy styles derived from old Kufic, but later inventions tend to be more creative and not easily measured the same way. Nastaliq is the most famous such an artistic invention.
In Nastaliq, the sizes are still measured in nuqtas but the letter joints are slightly higher than the baseline. This fact for consequtive letters builds oblique shapes that are no longer within straight boundaries, so glyphs can easily overlap on top of each other and the conventional kerning rules cannot be applied.
Also, while technically there is a limit on how far glyphs can descend from the baseline, no such limit exists for ascending glyphs. Though, as glyphs are typically 3-6 letters long, it is not considered a big issue.
For both Naskh and Nastaliq styles, there are flexible rules on where to put dots and vowels. Most calligraphers choose their position wisely in order to balance between positive (or non-empty) and negative (or empty) spaces. Also, kashidah is mostly used for beauty as long as to fill the line consistently, instead of stretching the spaces. However, kashidah must comply rules which requires a separate article to explain.
In the future, we are going to study about the kerning rules.