I posted this in the Oil Forum as well, but could be of interest for people interested in color theory and mixing too.
I've been working on finding the best (for me!) method for building up layers. I wanted to find the easiest, most economical way to achieve the effects I want in my end result. So I set up a systematic test, using two variations of four methods for six colors (yellow, red, blue, green, flesh, gray), so I could see their effects side by side. (These are of course not all possibilities for underpaintings. I disgarded many I considered inappropriate for my way of painting or those I've tried before and didn't like, so please note that this is not
an exhaustive list.) I figured that perhaps some of you here would find this useful as well.
a - In the underpainting I just painted the shadows, using the white of the board to create the lighter tones. The shadows where painted in their final values. Over this, I painted the halftones and lights in opaque paints.
b - Same as "a", but this time I used white to create the lighter tones.
c - I used an orangy wash (mix of raw sienna and venetian red) and wiped out the light parts and strengthened the shadow parts somewhat, but a whole lot lighter than their final values. Over this I painted the shadows in transparant paints (see below for colors used for shadows) and the halftones and shadows in more opaque paints (the lighter, the opaquer).
d - I used an even local color. No modelling whatsoever. Over this I painted just like in "c".
1- Starting on toned (dull yellow) panel.
2- Starting on white panel.
Because an image explains it better, the underpaintings (I forgot to take a picture before I began overpainting, so the most of the yellow spheres are already overpainted and ignore codes written in pencil):
Results in detail
For the underpaintings I used underpainting white, raw sienna, venetian red, burnt umber, prussian blue and permanent carmine, which are all quick drying pigments. These colors, apart from venetian red (and white of course), are also transparant, which is a quality I want in my underpainting, because I want to keep my shadows (not all of my darks per se!) as transparant as posible. With this limited palette, I can mix quite a large range of beautiful, deep darks.
The results were somewhat surprising to me. That's a good thing, because it means I haven't wasted my time with this test.
- The differences aren't as big as I had expected. The overall impression is pretty much the same, it's mainly a matter of nuances, but important ones. The dull yellow wash doesn't add too much to the end result, IMO.
- I would have thought that method a or b would give the best results, but I liked c and d better. I like the shimmering through of the oranges of method c. C is also the easiest and most fun, to me. In "a" it's very difficult to get a nice gradation.
- Method c gives a very pleasant, lively transparancy and a warm glow. Especially useful for skintones. I think the white background in "c" looks nicer as well. Method d gives a very solid look, albeit a bit "dead". Useful perhaps in some occasions.
From this test and from my experience gained so far with painting, I've come up with the following painting method. It's sort of a mix of method b and c (b for the lights and halftones, c for the shadows).
Step 1: I tone the board with a mixture of raw sienna and venetian red. I paint the underdrawing unto this, while still wet, then wipe out the lightest parts, to create form and paint in the occlusion shadows in their final values (I want these to lie deepest in the paint layers, for added sense of depth). Step 2: I begin painting the shadows with raw sienna, venetian red, burnt umber, prussian blue and carmine, keeping the shadows as transparant as possible. I then start laying in the halftones, with the same colors plus underpainting white and finally the lightest parts. Everything will now be (more or less) in its final values. The shadows will (more or less) have their final colors. The halftones and lights will be, due to the very limited palette of mainly earths, in grayed versions of the final colors. Grayed versions of warm colors will be cooler than their final colors, grayed versions of cool colors will be warmer than their final colors. Parts of the painting that aren't focal areas, will be mainly left in this stage. The focal areas will be embellished and enlivened in step 3, automatically creating color hierarchy.
Step 3: I finish the halftones and lights in the focal areas with their final, more saturated colors, making sure I let the second layer show through here and there. Because the final colors are painted over grayer versions of themselves, the final colors will shine and because of the temperature differences, there will be automatic temperature variations, creating visual interest. It's very important (and still somewhat difficult, I find) to paint the final colors in the same values as the colors in the second layer. If necessary I will adjust, deepen or enlive the shadow areas with glazes.
Step 4: Add the final details and highlights, small corrections and necessary glazes.
I feel that this method is a very practical, rational and economical way of painting to achieve the effects I'm after. I hope this information is useful to others as well.