Watermarks - Islamic manuscripts

‏(إهمال)‏ About ihmāl
The twenty-eight letters of the Arabic alphabet in fact consist of only
some fourteen different groups of base forms.
The letters in each composite group are usually distinguished from
those in the same group by dots or no dots. Those dots are written on
top or underneath the ductus (rasm in Arabic). Writing such dots is
called iʿǧām, ʻto provide with a diacritical pointʼ. Not writing such dots
is called ihmāl, ʻto neglectʼ, ʻto omitʼ, ʻnot-providing with dotsʼ.
The following fourteen groups of base forms are distinguished in the
Arabic alphabet: 1. alif; 2. bāʾ, tāʾ, thāʾ, nūn, yāʾ; 3. ǧīm, ḥāʾ, khāʾ; 4.
dāl, dhāl; 5. rāʾ, zāy; 6. sīn, shīn; 7. ṣād, ḍād; 8. ṭāʾ, ẓāʾ; 9. ʿayn, ghayn;
10. fāʾ, qāf; 11. kāf, lām; 12. mīm; 13. wāw; 14. hāʾ.
Each copyist has his own choices for providing the muhmalāt with
ihmāl signs. The alif, mīm, wāw and hāʾ are not really groupes and do
not need ihmāl signs. A copyist will not always use all possibilities.