How to do impasto oil painting digitally

To paint impasto digitally, use thick oil with a painting knife in Easel by Zaweba, a free painting studio for Windows, and turn on its movable light. Easel treats the height of the paint as a real surface, so the ridges and troughs left by the knife catch the light and cast shade, just as thick paint does on a real canvas. There is also an impasto knife preset to start from.

Impasto means paint laid on thickly enough that the marks stand up from the surface. On a real canvas it gives texture, catches light and shows every movement of the brush or knife. In Easel, height is part of the paint itself, which is what makes the effect believable.

Setting up for thick paint

Just Easel and a surface. Canvas, canvas board, linen or a gessoed panel suit impasto. A graphics card helps, because the lighting and paint are computed on the GPU; a mid-range card handles an A3 sheet at 300 DPI, and a basic chip works with wet paint moving a little slower.

Building the ridges

Start with the impasto knife preset if you want a ready setup. It is one of 28 built in. Otherwise choose oil as your paint. Oil stays wet, mixes on the canvas and builds impasto, and like the other wet paints it has Water and Thickness settings. Raise the thickness and keep the water low.

Choose your tool. Easel has four painting knives and a palette knife among its brush shapes, plus stiff hog hair brushes. A knife lays down flat planes with sharp edges; a brush leaves ridged strokes.

Load the paint. You can squeeze paint onto the physical palette, mix it with the knife and load from the mix. A thick, well loaded stroke is what builds height.

Lay the paint down, then look at the light. Easel's light has a direction, a height and a relief setting. A low light from one side throws long shadows and makes every ridge stand out. A high light flattens the texture. Move it until the surface reads the way you want.

Add more paint where you want weight. Impasto is often kept for the brightest passages, while the shadows stay thin, which is how many painters use it on real canvas.

Keeping texture and colour in balance

Do not let the impasto hide your colour decisions. Flat light (L by default) turns the relief off so you can judge colour on its own, then switch back to see the texture. Values and squint views, which never change the painting, are also handy for checking that the lights and darks still work under all that texture.

Work while the paint is wet. Oil stays workable for about 10 minutes of real time, and the drying speed slider stretches or shortens that. Pushing a knife through wet thick paint drags it into new ridges; the metal scraper goes further and shoves wet paint aside to reveal what is underneath, which is good for sgraffito-like marks.

Watch the tilt. Thick oil barely moves when the canvas tilts, but thinned paint will run, so keep the canvas flat (Ctrl+0) while building texture unless drips are part of the plan.

Modelling paste, impasto gel and sand gel are among the paints added in version 1.1, if you want texture that is not oil.

Exporting textured work

When you export to PNG, JPEG or TIFF, you choose whether to include the impasto lighting. With it, the picture shows the ridges and highlights; without it, you get flat colour, which is useful for printing or for further editing in Paint by Zaweba. Exports can be at 1x or 2x.

Save as .zeasel to keep the paint wet for another session. Undo keeps 80 steps by default, so you can try a bold knife stroke and take it back if it buries something you liked.

Practising before using real paint

Real impasto uses a lot of paint, and a thick layer takes a long time to dry. Practising the knife strokes and the placement of thick paint on screen first is cheap, quick and teaches you where texture helps a picture and where it just adds noise.