I have since learnt that in watercolour painting, the use of the split primary palette is fairly well established. This takes my three primary colours listed above, and splits them into cool and warm -- so a cool red and a warm red, a cool yellow and a warm yellow, and a cool blue and a warm blue. But then it seems to get complicated when you start mixing them together. For example, I guess that green should be mixed from a cool yellow and a cool blue, but what if a warm colour is used instead?
Presumably with practice it becomes second nature to mix colours using a split primary palette? However, this does seem to raise the bar -- unnecessarily? -- for beginners, who may struggle with colour theory as it is often presented. Perhaps this helps to explain why some people use palettes with a large number of colours, as it is too much of a chore to mix them from primaries? (I have ignored the discussion of staining and granulating pigments, as that is another dimension!)
In the course of browsing the Handprint pages, I discovered the idea of using a secondary palette instead. This made a lot of sense to me. No longer did I need to worry about whether I needed to use the cool or warm primary colour, because the primaries had been changed to three that I recognised from computer colour printing (cyan, magenta, yellow [CMY]), and three secondary colours had been introduced (red-orange, green, blue-violet). Furthermore, the gamut of the palette had been increased -- especially for greens.
I was then pleased to find out that the selection of paints in my Cotman Sketchers' Pocket Box readily lent themselves to a secondary palette: Cadmium Yellow Hue would be primary yellow, Cadmium Red Pale Hue would be secondary red-orange, Alizarin Crimson Hue would be primary magenta, Ultramarine would be secondary blue-violet, Intense Blue would be primary cyan, and Viridian Hue would be secondary green.
Further reading of the Handprint pages led to more specific recommendations of primaries and secondaries. Restricting myself to the Winsor and Newton Cotman range, I replaced Cadmium Yellow Hue with Cadmium Yellow Pale Hue, and Alizarin Crimson Hue with Permanent Rose to closer match the suggestions. The Cotman Intense Blue is PB15 rather than the PB15:3 (Phthalo Blue Green Shade) that is suggested, but I was happy with that. If I was fussy about single pigment paints, then Winsor Yellow and Winsor Orange (Red shade) from the W&N Professional range would need to replace the Cotman Cadmium Yellow Pale Hue and Cadmium Red Pale Hue respectively. (I have since found that the Daniel Smith Transparent Pyrrol Orange gives a closer match to Cadmium Red Pale Hue than Winsor Orange (Red Shade).)I have been regularly using my Cotman secondary palette since late 2014. Even though I was a little unsure at first as to whether the [CMY subtractive] primaries would work as expected, I have been delighted with the outcome. I have had no trouble at all in mixing the colours I want. (See the crude colour wheel at the top.) My mind has not been cluttered by "rules" of what I should (or should not) mix with what. By alternating the arrangement of primaries and secondaries in the palette, I can easily find the complementary when I need to tone down a colour or mix a chromatic grey. (The row of pans at the bottom corresponds to the row of colour swatches at the top.)
So my question has now become: "Why is the split primary palette still often taught to beginners in exclusion to anything else?" (Or to put it another way, why don't computer and commercial printers use split primary colours? Hmm...)
