The wireframe was generated in photoshop (more like approximated by me). Once again, it is not how you would necessarily work on a portrait painting. Rather, it is more of a symbolic gesture towards the early stage construction techniques you would use (like in the Loomis method). For the final image, I masked the portrait in a diagonal stripe. I was playing around with various ideas, and when I saw the diagonal lines, I kinda liked the look of it. It might have stemmed from my initial intentions to split the face vertically into 3 parts, each part being a different render level (realstic, line drawing, and polygonal). I couldn't get it to work exactly right in a static image (I am still thinking of using this concept for my web portfolio, where the sections will be animated), so I moved towards a more gradual reveal of the layers.

As described below, I added some of the line drawing to part of the face. I did not actually go through this stage this time, but I've done it in my previous works, and it is very useful. I still play around with Ambient Occlusion drawing from time to time, and the line work is extremely helpful in those situations. Line work is also very important if you are planning to construct a face from imagination (which is ultimately my goal).

Now that the portrait itself was done, I wanted to move into the actual art piece I was trying to create. My goal with this is to showcase the different stages of a drawing process, all in the same painting. I've experimented with quiet a few ideas - different levels of 3d renders (painted on top, not generated in 3D programs), unfished brush work, etc. To make it visually pleasing (yet at the same time not as accurate, in terms of how I actually painted this portrait), I decided to add a layer of line work (like a pencil sketch) and a layer of a very low poly 3d render. In this particular picture, I masked out parts of the face to make room for those layers. Here I used some custom splatter brushes, but up till now, it was all done with the standard hard-edge round brush (with some cleaning up using the soft-edge round brush closer to the end)

Played around with the colors. Kept a more red tint in the middle section of the face (cheeks and nose), but removed some of that coloring from the forehead (which actually tends to have a bit more of a yellow coloration due to the bone underneath). Added a bit of blue for the shoadows in the bottom part of the face.

Now that the values are done, time to move on to color. Applied a very rough color layer, mostly in Color mode, to get something to work with. It is starting to look like the skin color, but it's rather dark and uniform all through out. 

Adding more details, like hair and highlights. Also, thanks to some valuable feedback from a friend, smoothed out some parts of the face, like the cheeks, to give it a bit more of a realistic look.

Things are starting to look way better here. Fixed the eyes, worked a bit more on the hair, and added more volume to other features of the face. However, I think the most important thing is the filling in of the hoodie. "Neck-less" head was looking kinda creepy by itself, so an addition of the shoulders was a good move. 

Here I started addressing some of the problems mentioned below, by first and foremost, adjusting the angle of the face and fixing some of the proportion issues. Once again, it is starting to look more like the reference (though still some issues with the eyes). Either way, I can now focus more one moving forward with the details.

Once I felt the underlying "scaffold" was good enough, I moved on to actual painting and filling out some of the forms. As you can see here, it wasn't a very smooth start, as I've actually lost some of the 3d depth and the face now looks like it is skewed.

Here I did try to split the face into the basic polygonal shapes as in the Loomis method, but I mostly did it for my final effect, rather than as an actual construction technique. As I explained above, the purpose of this painting was to visually show different stages of a portrait painting process, hence the basic 3d geometry. That said though, drawing the lines did actually help me with outlining the lips, knose and eyes, as they made it easier to judge relative distances between the features

Instead of drawing everything by hand eye coordination, I try to improve my face construction techniques. My goal is to become more profecient in the Loomis method, but for now I rely on a few anatomy shortcuts to get a rough sketch going. I tend to use the equilateral triangle to get the position for the eyes and lower lip. Veritcally I rely on the equal distances between chin to bottom of nose, then to eyebrows, and to the hairline. Once I lay these basic rough measurements, I then try to adjust anytihng that may be different in the actual reference.