Wet on wet means working new paint into paint that is still wet, so the two blend on the canvas rather than being laid side by side. It is how skies, mist, water and soft edges are made. None of it needs special equipment — what comes in the kit will do it, provided the paint has not thickened.
In oil it is easy, because oil stays open for hours. In acrylic you have minutes, and almost every complaint people have about acrylic comes back to that single fact.
A clarification worth making first
The phrase is used for two different things and they get conflated constantly.
The general technique is what this article is about: blending wet into wet, in any medium.
The wet-on-wet method most people have seen on television, associated with Bob Ross, is a specific oil painting procedure. It starts with a thin coat of a slow-drying white applied over the whole canvas, and everything else is worked into that wet layer. It is not an acrylic technique and it cannot be reproduced with acrylic, because the base coat would be dry before you began.
If you have tried to follow one of those demonstrations with acrylic paint and found it impossible, that is why. It was not you.
Four ways to extend the window
1. Retarder medium
The direct answer. A retarder is a medium that slows the evaporation that makes acrylic set, and it can take you from a few minutes to twenty or thirty. It is the thing most people wish they had bought sooner.
Use it sparingly and mix it in properly. Too much retarder gives you paint that stays tacky for a long time and never quite hardens.
2. A damp palette
A sheet of damp paper towel under a piece of baking parchment, in a shallow tray. Paint on that stays workable for hours rather than drying on the plate between strokes. It costs nothing and it is the single best habit in acrylic painting.
3. A fine mist of water
A small spray bottle, held well back, over the area you are working. Not a squirt; a mist. Re-wetting the surface buys you time on the canvas the same way a damp palette does on the palette.
Do not use this as a way of thinning the paint. Water dilutes the binder as well as the pigment, and past roughly a quarter water you get a chalky film that can lift when you work next to it.
4. Work small
The most reliable of the four and the one that needs no purchase. Do not lay a whole sky and then try to blend it. Lay two adjacent bands, blend where they meet, and move along. Blend one join at a time and the window is never a problem.
What it is good for
- Skies and graded backgrounds. Two or three bands of color, softened only where they meet.
- Water. Horizontal strokes pulled through each other while wet, which is what gives water its blur without losing the direction.
- Mist and distance. Softening the base of a hill into the sky behind it is what makes it sit back in the picture.
- Rounding an object. The transition from the lit side of an apple to the shadow side is soft in life and hard on the canvas unless you blend it.
What it is bad for
- Anything with an edge. Rooftops, masts, window frames, lettering. These want dry, hard edges and blending them destroys the object.
- Detail. Fine work goes on top of a dry layer, at the end.
- Dark over light. Pulling a dark into a wet pale color drags the dark everywhere and never comes back cleanly.
How it turns to mud
Mud is not a mysterious failure; it is a predictable one, and it has three causes.
Blending complements. Any two colors opposite each other on the color wheel neutralize each other when mixed. Blend a wet orange into a wet blue and you get gray-brown, every time. If two adjacent regions are complementary, keep the edge and do not soften it.
Overworking. Every extra pass with the brush mixes more. Two or three strokes along a join, in alternating directions, and then leave it. The urge to keep tidying is what ruins a soft edge.
Working a half-dry surface. This is the specifically acrylic failure. Once a passage has started to set, dragging a brush through it tears the film and lifts color instead of blending it. If it is no longer glossy, stop. Let it dry completely and go over the top instead.
The one-brush rule
Use a clean, barely damp brush for the blending itself, not the one loaded with color. Load and place the two colors, then take a second dry brush, wipe it, and use only that to soften the join. Blending with a loaded brush is just adding more paint.
On a numbered canvas
Numbered kits are designed to be painted region by region with hard edges, and filled in correctly they look right. Softening two or three joins is nonetheless the quickest way to make one look observed rather than filled in.
The places worth doing it are the same ones as in any painting: the boundaries between bands of cloud, the far edge of water, the base of distant hills. Not the rooflines, not the boats, not the trees against the sky. Two or three joins on a whole canvas is the right amount, and it is covered along with the other finishing techniques in how to make a paint by number look painted.
For the opposite approach, building a picture in dry layers, see layering acrylic paint and underpainting with acrylics. If you want a medium where wet on wet is the default rather than a race, watercolor is the one, and our guide to acrylic paint sets covers the mediums mentioned above.
