Knife painting is a form of impasto painting where the paint is applied using a painting knife, or palette knife. The paint is applied in thick layers using the edge of the knife. Impasto mediums (above) can be mixed with the paint to increase thickness.

Painting knives can be used in many ways for painting: to mix the paint on the palette or directly on the surface; applying different colors of paint in thin layers; and the blade can be used to scratch off small areas of paint while still wet to reveal the paint underneath, like in the sgraffito technique.

Depending on the shape and size of the painting knife used, you can produce different effects.

Painting knives are different from palette knives: the blade is bendable and the handle is cranked, to keep your hand away from the painting surface.

Text source: https://feltmagnet.com/painting/Acrylic-Painting-Techniques