Again, I'm overwhelmed by the response and support you've all shown me with this series. Thank you.
I want to also thank Ariel Gulluni who has donated his time and energy to translate Webisode 1 Part 1 into Spanish. This generosity will allow many more people to easily access this information. The captions are available when you view the webisode on Youtube. Thank you Ariel!
Okay, now to answer some of your questions. Originally, I envisioned writing out each question and answering them in turn. However, I realized that many of the questions and answers relate so it might be better to answer in an essay form.
For starters, I like to use a smooth, portrait linen, 2-4 times primed. In the past, I used oil primed linen but lately I've come to prefer the absorbency of acrylic-sized linen. I stretch the canvas tightly on Frederix stretchers (any brand would be perfectly fine) using stretcher pliers and a staple gun.
Before starting, I tone the linen with Raw Umber oil paint thinned with Mineral Spirits.
I use synthetic round brushes; their size varying roughly in proportion to the form I'm painting. The forms of the eye I painted in this past webisode were similar enough in size, so I did not need to change my brush size. Were I to then paint the forehead, I would switch to a brush that is more in proportion to the size of that form.
I mostly do not require any medium as I typically use the body of the paint from the tube. I do have linseed oil on standby and occasionally use it if I encounter a pool of paint that needs a little extra fluidity. I prefer to paint form opaquely as I want to have my mixtures on the palette have a predictable result on the canvas (were I to paint thinly, whatever I mix is changed by the properties of the canvas' tone showing through).
Now to color and my palette. I could simply answer this with a list, but I think that it would be unhelpful without briefly stating my views on color selection before and during the course of painting. My interest in color and its application has always been driven by the concepts I use to interpret and model form (by this I mean, mixing up tones that reflect my physical understanding of the optical phenomenon in front of me). I may attempt a one-for-one match to the colors before me or I may transpose and/or compress my color(HVC) range according to some particular artistic goal--this deliberate alteration, to have a plausible result, must be guided by an understanding of the physics of light. So, when I describe my process as consisting of me identifying the local (intrinsic) properties of an object and how my ability to see those properties diminishes as the form receives less light (thus decreasing in value and chroma) I am answering the "how" part of what I do. To successfully mix the colors you've interpreted certainly requires experience but follows this fairly simple logic originating with the local (say Red), recognizing the form type (say a sphere), the light most facing plane (therefore, the lightest in value and chroma) and the visibility of these properties as less light is received (therefore darker in value and less chromatic). This translates to mixing up a Red on your palette (an optical match to the Red in life can be attempted or, should you choose, be transposed to an alternative tone provided it subsequently follows a physical logic). From there, you search about on your palette for other pigments that will diminish the value and the chroma while keeping the hue stable. For example, if you began adding only Ivory Black to your Red, you will certainly be diminishing both chroma and the value, but you'll also be pulling the Red off of a radius to the neutral, thus shifting it towards a low chroma Violet. You then think directionally in color space and ask what might take you back towards center Red while maintaining the downward path of value and chroma. You could try Raw Umber and in a particular situation, that might be enough. If not, other colors are called upon (this should indicate the primacy of concepts over learned mixture patterns). It is the understanding of what's physically happening that keep us out of the wilderness of bizarre coloration. It also let's us follow a logic that is relational and not necessarily dependent on the optical. I find this very liberating artistically.
As far as colors on my palette I try to have highly chromatic representatives of each part of the color wheel so that I can maximize my mixing range. On an average day, I have Titanium White, Yellow Ochre (as my low chromatic yellow), Cadmium Yellow (as my high chromatic yellow), Cadmium Orange (high chroma), Cad Red (high chroma), Alizarin Crimson, a couple flesh tones (tubed or pre-mixed) as short cuts (keep in mind, these are clearly recognized as low chroma, particular values of a given hue--not blindly as a flesh tone to be used necessarily in the painting of flesh), Burnt Umber, Raw Umber and Ivory Black. Were I to paint something that had a local blue, green or violet hue, I would undoubtedly have a high chroma representative of that particular hue on my palette.
Throughout all of these answers I hope it is evident that I don't impose strict material practices on myself. It is a flexible, evolving set of habits that have developed out my best attempt to effectively paint form in space in a way that convinces the viewer while transmitting my original artistic vision.
This may leave some questions unanswered but not to worry, more webisodes will be coming soon!
Thanks for the excellent questions and the continued interest!