I should also note that Caso (1958; 1971:345) places the start of any particular day at noon. I suppose then, that today's entry should actually address 13 Tecpatl (13 Flint), as I'm typing this after noon. This day would then end the trecena, with tomorrow hosting the start of the new trecena, 1 Quiahuitl (1 Rain). That would make today quite significant, as preparations should be made for the coming descent of the Cihuateteo, as the day 1 Quiahuitl is one of the days that they return to earth to wreak their particular type of havoc (see Sahagún book 6). More on this 'moveable feast' the day after tomorrow then.
According to Sahagún (6:39) the day 11 Cozcachuahtli was a good one, and accordingly one born on that day "would grow old; he would become bent with age. The sun would fulfill him and take him into his house." Growing old was a good thing in Aztec Tenochtitlan, you will recall. Among other things, the aged had unlimited access to pulque! Nevertheless, 12 Ollin and 13 Tecpatl were also good days, as Sahagún adds, noting that they were all lifted by the providential tide of 10 Cuauhtli.
In terms of the tonalamatl then, particularly Codex Borbonicus 6, we are still in the 1 Miquiztli trecena presided over by Tezcatlipoca (as Titlacahuan/Yaotl Tezcatlipoca) and Tecciztecatl. The day lord for 11 Cozcacuahtli is Mictlateuctli, for 12 Ollin it is Tlahuizcalpanteuctli, and for 13 Tecpatl it is Ilamateuctli/Mictlancihuatl. On Borbonicus 6, Mictlanteuctli appears with black body/face paint, with red around the mouth. He wears the typical white paper rosette (cuexcuchtechimalli / ixcuatechimal) device in his circlet, and it is topped by a turquoise diadem with a grey/white striped (turkey?) feather and quetzal feather panache. The paper rosettes mark this figure as an underworld deity, while the diadem (xiuhuitzolli) serves as a semantic indicator for the -teuctli portion of his name.
Tlahuizcalpanteuctli has some of the more varied depictions in the Borbonicus, at least in his inclusion as day/number lord. For Borbonicus 6 he appears with a red leather circlet topped with his usual teardrop-shaped motif. His feather panache is made of white and quetzal feathers. As did Mictlanteuctli, he wears a turquoise earspool with red and white paper(?) streamers attached. As well he has a small golden curl that descends from the back of his earspool, possibly the descending curl of his blond hair (quite a few of the day and night lords are shown with blond hair in the Borbonicus). He has yellow body paint with red at his mouth and black around his eyes. Ilamatuectli, day-lord of 13 Tecpatl, is depicted as a variant of Mictlancihuatl (compare her to the version of Mictlanteuctli shown as the night-lord for 12 Ollin).
ye ixquich