How to use a palette knife in digital painting

A palette knife in Easel by Zaweba, a free painting studio for Windows, does the same two jobs as at a real easel: to mix paint on the palette, and to lay or push wet paint on the canvas. The palette knife is one of the brush shapes, alongside four painting knives, and the metal scraper pushes wet paint aside into ridges and reveals what is underneath.

Knives give a different kind of mark from brushes. A brush leaves bristle tracks and soft edges; a knife leaves flat planes, crisp edges and ridges where paint piles up at the sides of the blade. Those qualities are why knife work suits rocks, buildings, rough seas and bold abstract pictures.

Two jobs for one blade

The first job happens off the canvas. Easel has a physical palette: you squeeze paint onto it from a colour set, then mix it with the knife. Paint is pushed and folded as you mix, never lost, and you can load your brush or knife from any mix you have made. Colour mixes as pigment does, using the Kubelka-Munk model, so the mixes on the palette look like the mixes you would get with real paint.

The second job is painting. On the canvas a knife spreads, scrapes and drags paint. It works best with paint that has some body, so oil, acrylic and the impasto and modelling paste gels added in version 1.1 are all good partners.

A knife painting from start to finish

Choose a surface that can take thick paint, such as canvas, canvas board, linen or a gessoed panel.

Pick oil or acrylic and raise its Thickness setting. Thin paint spreads into a film; thick paint stands up in ridges.

Squeeze two or three colours onto the palette and mix a few values with the knife. Leave some streaks unmixed, since loading a knife from a partly mixed pile gives broken colour on the canvas, a favourite knife-painting effect.

Select the palette knife or one of the four painting knives and lay down a stroke. Short strokes with plenty of paint keep edges sharp.

Turn on the movable light. Paint height is lit with a light you can set for direction, height and relief, so knife ridges catch highlights. A low side light shows texture most strongly.

Use the scraper when you want to take paint away rather than add it. It pushes wet paint aside into ridges and shows the layer below, which gives a scratched, revealing mark.

Habits of good knife work

Work wet. Oil stays wet for about 10 minutes of real time and acrylic dries fast, so plan knife passages for oil if you want to keep moving paint around. The drying speed slider, from 0.25 to 4 times, stretches or shortens the open time.

Keep the knife clean between colours if you want them pure. Brushes get dirty when dragged through wet paint, and C cleans and D dips by default.

Judge colour with flat light. Pressing L turns the relief off so texture does not fool your eye, then switch it back on to see the ridges again.

Do not cover everything. Knife texture is strongest when it sits next to calmer, thinner areas, so leave some passages smooth.

Related tools worth knowing

The finger smudges and the rag lifts paint, both useful around knife work. Sponges and a roller give other broad marks. The sgraffito stylus, comb and colour shaper scratch and shape wet paint for finer texture. And there is an impasto knife preset among the 28 built in, which sets up a knife and thick paint in one go.

When you export, you can include the impasto lighting or leave it out. Saving as .zeasel keeps paint wet, so a half-finished knife painting can wait until tomorrow without setting.