itztli (Mdz30r)
This element for an obsidian blade (itztli) has been carved from the compound sign for the place name, Tzinhuitzquilocan. It is an upright leaf shape, an oval pointed at both ends, much like a flint knife (tecpatl). It is black with four white teeth running vertically up the left side. The teeth are surrounded by a curving red line that suggests gums.
Stephanie Wood
Offerings from graves found in the Templo Mayor (see below) show how these types of blades could be decorated with faces. Also, John Montgomery has reproduced drawings of flint knives in Nahua and Mixtec manuscripts. The ones on the left and right are from the Codex Mendoza, and the one in the middle is from the Mixtec manuscript that was formerly called the Vienna.
Stephanie Wood
c. 1541, but by 1553 at the latest
Photo, by Robert Haskett, of Offering 125, taken 2/25/2023.

itz(tli), a sharp-bladed instrument of obsidian, https://nahuatl.wired-humanities.org/content/itztli
obsidian knife
Codex Mendoza, folio 30 recto, https://digital.bodleian.ox.ac.uk/objects/2fea788e-2aa2-4f08-b6d9-648c00..., image 70 of 188.
The Bodleian Libraries, University of Oxford, hold the original manuscript, the MS. Arch. Selden. A. 1. This image is published here under the UK Creative Commons, “Attribution-NonCommercial-ShareAlike 3.0 License” (CC-BY-NC-SA 3.0).