The Sumerian word na-IZI (qutrēnu = incense) is to be read na-de3. The verb that is usually used with this noun is si(g), “to pile up,” in the phrase na-de3 si-ga. This collocation appears in two Ur III tablets; in the ritual text PBS 13, 35 obv. 5 and in the recently published Umma text SANTAG 6, 100 obv. 3. Gudea Cylinder B iv 4-5 reads dnin-dub išib-mah eriduki-ka-ke4 na-de3 ba-ni-si: “Nindub (...) piled up incense.” The expression further appears in a few Old Babylonian literary texts (Iddin-Dagan A 147 and 196 and Home of the Fish 4); in Old Babylonian incantations (e.g. YOS 11, 56 obv. 6-7); and in later bilingual compositions (see CAD s.v. qutrīnu).
The reading na-de3 rather than na-izi is demonstrated by the Old Babylonian Kusu Hymn l. 22: [x im]-mi-in-si na-RI si-ga (YBC 9860; see P. Michalowski in Fs. Hallo p. 153). Here, the same collocation is found with the spelling na-RI, to be read na-de5. A second attestation of this spelling is lu2 = ša II iii 22': na-de5-⌜ga⌝ igi-bar-ra = min (=barû) ša qutrinni (MSL 12, 120, and cp. MSL 16, 344, 52'; for the reading of lu2 = ša II iii 22' see CAD s.v. qutrīnu).
The alternative spelling na-de5 was used alongside the traditional na-de3, and may have been introduced to suggest an association with the expression na-de5, to purify (elēlu).