Here is my take on washes...
Washes are most effective when they are employed to meet a desired finish. By that, I mean that using similar and dissimilar materials can GREATLY affect how the wash acts. If you paint the base with an Acrylic, and then use an acrylic as a wash, the wash is likely to leave a slight tint on the overall surface of the base. This is true whether you use a surfactant or not. I have found that using dissimilar materials tends to quell this from happening. Therefore, I generally use an oil wash over my base that is either the acrylic color or a clear coat like Future.
The other thing that seriously effects how a wash lays is the actual surface of the paint to which it is applied. A mat surface is more likely to be "stained" by the wash than a semi or gloss surface. This can be used to the advantage of the model maker, when they want differing effects on a piece. For instance, I will gloss coat a subject and do the panel lines etc. as well as washes to bring out details (cracks and crevasses in the detail piece). I will then go back and flat coat the same piece if I am adding stains or smudges with a wash.
Here you can see how the “staining” effect can be used as an advantage in getting a desired finish. The fur was washed with layers of oils over a flat white base. The details were “picked out” with an artist’s kneadable eraser, which is very effective at removing color that has been laid down on a subject.
Fur
I tend to use Oil washes the most as I find they can be controlled to a much greater degree than other types.
I will occasionally use an acrylic wash if I want to overall darken a subject and knock back a brighter tone.
As to the water color thing, if it is not flowing then get some watercolor medium from Windsor and Newton. It is a surfactant that is specifically designed to increase the flow of watercolors and it slightly slows the drying process.
Cheers,
Mark
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