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Gouache pigments are mostly opaque and consist of powdery materials, which are fixed with glue and have strong coverage. So when you draw gouache, you often start with the darkest color.
Gouache pigments can be covered layer by layer. If you are patient, you can draw the same effect as an oil painting, but the color of the pigment is darker when wet and lighter when dry. There are also purplish colors such as rose red and violet, which are easy to turn out. So don't use it as a primer. Gouache paints are very fine in color particles, which are beautiful after being dissolved in water, but they cannot cover the background color. The colors of ultramarine, ochre and earth red in watercolor pigments belong to mineral pigments, which are easy to precipitate when used alone or mixed with other colors.