If experience is any judge, I'm around half way to finishing this icon. Today, I worked on stabilizing the colours of the cape. It's not usual to allow the inside folds of a cape to have its own shadow colour in Byzantine imagery.
I've known before, but learned yet again through a personal wrestling match with obstinate ignorance, that red does not cover very well. The crimson on the top is several layers thick, yet the black cartoon lines show clear through the pigment. My solution was to alternate red and white layers. White is chalky and blotchy, and also does not cover well. However, the colours that do cover well don't play nicely with red. I think that the red and the white in alternating layers allowed my to create the cover I wanted, but it took many layers to achieve.
I've also noticed that some of the other colours, notably the blue, has separated after drying. The pigment has unlatched from its medium. This is disappointing. Likely, though, I can fix the blotches when I apply the final sealant at the end of the project.