As a pre-word: I am using the terms "white-based" and "saturated" color, this is not an official naming for the types. But basically you can categorize acrylic colors like that more or less easily.
Now to the main message:
I've been painting purple currently and this is one of the colors that really can give headache and the order in which to blend is very important with purple. I am using a pink and white for highlighting.
1) If you basecoat purple and fade it over with pink or white, the saturation is lost big time and the layer looks gray-ish very fast, even if the blended layer was as thin as possible. It entirely destroys the look.
2) If you basecoat pink and fade it dark to purple, it receives a very strong saturation where the mid-tones between pink and purple are really really strong and might get a red-ish touch. White layers on pink on the other hand is no problem, since pink is "white-based" anyway.
So I always differ when blending to decide from which starting color to which end color I want to blend:
Is the color a saturated color or a white-base? Meaning: Is it possible to receive the same color by mixing white with another color or not? Light blue, pink, Bleached Bone surely are and even some greens (especially Coat D'Arms greens) might be of that type. Purple, brown and red mostly are mostly of that saturated type.
The order of painting then is: Paint the white-based first, then blend over the saturated color. That keeps a good saturated blend. Also it might be a mix. For example:
- Basecoat Vomit Brown (white-based)
- blending dark Flesh Wash (saturated type)
- highlighting with Bleached Bone (white-based)
As you see, a saturated was used to darken the base-coat, but a white-based was used to brighten the white-based basecoat.
As an example, here's a shot of what I'm talking about:
The left image is the original, the right one is with increased digital saturation to better show the difference. In real they are a tiny bit better to see than in the original, but I also want to point out the major thing I'm talking about.
The green marked area is a blend entirely made from pink to purple, leaving in the middle a very saturated color mix. The red areas had to be reworked, meaning I had messed it a bit and needed to paint with pink again which caused desaturation. A thin layer or purple gave back a little of the saturation, but not too much. That's why its more gray-ish.
Well, the essentials of my long talk maybe help you to paint such a difficult color as purple, but also to paint other colors that have the similar saturation-problem. If you blend opposite, meaning a white-based onto a saturated, then you not only lose saturation, but also very fast receive layers which simply don't want to blend with the rest, no matter how thin you go, they might look odd, gray or give the impression of a too thick painted layer, even if it wasn't. That's the effect of the white stuff in these colors.
The reasons behind this are:
- A white-based-color has very strong bright pigments which reflect more light themself than letting color going through and has nearly no transluciency. The pigments are opague themself, the light gets reflected. As if you put some milk-glass in front of a picture.
- A saturated color has always some transluciency (the pigments are or seam to be translucient themself) which causes in thin layers to give the belower layer to give a different hue without blocking the light entirely. It gets slowly absorbed while passing though the color. As if you put a clear colored glass in front or a picture.
As a last note: Some people prefer the non-toon-like-painting (which definetely is my favorite) and they darken always with a black-mix of the base-color and highlight with a white-mix of the base-color. That gives in the end a far more real look, but for me looks too much like our real gray world.
However, these painters of course always blend from the saturated base-coat towards the blackish shadows and towards the whitish highlights in this order, since their goal is not to keep the saturation like it is mine.
