Saint Justina of Padua, Bartolomeo Montagna (Bartolomeo Cincani)
In the collection of the Metropolitan Museum of Art. Use the “download or Enlarge links under the image on their site.
Though this is technically a religious work, not a portrait, I think the beautifully drawn and delicately rendered face has the look of a real person, not an imagined ideal.
I like the wonderful detail in the texture of the iris of the eyes, and the highlight in the eye (which, for reasons beyond me, some artists in later centuries would leave out).
The values in which the face is modeled are subtle but the face feels well defined and geometrically strong.
Montagna’s style shows the influence of Venetian Renaissance master Giovanni Bellini, and it’s speculated that he may have been a student or apprentice of Bellini at some point.