Telum, the "weapon" aspect, is composed of Instrumentum and Ignis. (Before 4.2.2, it was Instrumentum+Perditio.) It is found in all weapons, but arrows are a perfect source. Note that use of a centrifuge allows getting twice the Instrumentum out of a pile of flint, by crafting the flint into arrows (4 apiece), distilling those, and centrifuging the resulting Telum.