0:09 Hello, I'd like to compare two ways of mixing colour; atomic mixing and optical mixing. Atomic mixing is the physical combining of colours with one another on the palette. As the name implies, the pigment particles are combined in the same paint film to achieve the desired mixture. Optical mixing is when one colour is laid in a separate glaze, or scumbled film, over another to create a third colour.
0:54 I'm layering Alizarin Crimson over pale blue, to create an optically mixed violet. Further layering can make the mixtures more complex and interesting. Atomic mixing has the advantage of being predictable once you've learned the capabilities of your chosen palette. I can mix the colours together rather than waiting for a layer to dry. And I can also mix more than two colours together in one process.
1:26 Optical mixing has its own advantages as well. One of which is that by relying on layering transparently or semi transparently, some depth can be created in the painting. Also mixtures made optically can seem more radiant than atomic mixtures. Perhaps the element of surprise when putting one colour over another is also an advantage when experimenting. These scumbles seem really charged-up by their underlying colour. One disadvantage with optical mixing is that it does rely on the underlayer being dry before another can be put on top.
2:11 By adding a medium such as Winsor & Newton Liquin light gel, I can accelerate the drying time and still get good clear layers and the best optical effects. The use of coloured grounds could also be an effective way of experimenting. One form of mixing is no better than the other and shouldn't stop you combining the two in the same work if you want to.
I hope this has helped you understand these two ways of mixing colour!