Underpainting also has the additional advantage of being visible through other glazed layers on top of it and thereby influencing the finished painting. By using an acrylic layer as an underpainting one has all the advantage of an oil underpainting while also saving time. The What and Why of Acrylic Acrylic is a polymer-based medium and is essentially plastic in nature. The rapid drying time that can be a disadvantage when one wants to develop and blend a painting, can be a blessing when the artist wants to establish the painting quickly. Acrylics can be applied using all the normal oil based painting techniques, including glazing.
Acrylics respond very well to thinning and can be painted over in fairly rapid succession.
One can also paint thickly in an impasto style with acrylics. Although many critics of acrylics claim that this medium does not adhere well to canvas, this is not the case in practice. Acrylics will adhere well to the rough surface of a canvas board or a stretched canvas frame. All one needs is a basic set of acrylics and water or acrylic medium that is especially manufactured for thinning the paint. Begin with a wash on the canvas.