In Ilkorin, it seems that [z] vocalized into [i] before voiced stops, similar to developments in Old Noldorin. The clearest examples are ᴹ✶mazgē > Ilk. maig¹ (Ety/MASAG) and ᴹ✶mizdē > [miid(e) >] Dor. mîd (Ety/MIZD).

The vocalization after [e] are less clear. There are two examples: ᴹ✶ezdē > Ilk. Êd (EtyAC/EZDĒ) and ᴹ✶mizdā > [mezda >] Dor. mêd, where the second example would have developed a medial [-e-] due to Ilkorin a-affection. In these examples, it is possible that the [z] became [e] or simply lengthened the preceding vowel, so that the development was [-ezd-] > [-ēd-]. However, the [z] could also have vocalized into [i] as it did after [a] and [i] if the resulting diphthong [ei] became [ē] afterwards: [-ezd-] > [-eid-] > [-ēd-]. This second development is the theory used here.

There are no attested examples of the vocalization of [z] after [o] and [u] or before [b], but presumably the developments would have been similar, probably resulting in [oi] > [ui] and [ui], respectively.