How do I lay a flat watercolour wash without streaks?

A flat wash is one continuous bead of paint dragged down a tilted board. Break the bead and you get a streak; run out of paint halfway and you get two washes.

Difficulty: intermediate
Time: 20 min
Read: 4 min

Short answer

Mix far more paint than you think you need. Tilt the board about 15 degrees, load a large brush and lay a horizontal band across the top, then the next band just overlapping it so the bead of paint at the bottom of the first is picked up. Keep going without stopping, and lift the final bead off with a squeezed-out brush.

Everything about a flat wash comes down to one thing: a bead of wet paint sitting along the bottom edge of what you have just laid. As long as that bead exists and you keep meeting it with the next stroke, the wash will be even. The moment it dries or you run out of paint, the wash is finished whether you are or not.

Step by step

Mix at least twice as much paint as you think you need.Running out mid-wash is the commonest cause of a ruined one, and you cannot mix more fast enough or accurately enough. Mix it in a well or a saucer, not on a flat palette.
Wet the paper first if you want maximum evenness.A wash laid onto damp paper flows more evenly than one onto dry, at the cost of some control over the edges. Both approaches are valid — dry paper gives crisp boundaries, damp paper gives softer ones.
Tilt the board.Around 15 degrees. Gravity is what forms and holds the bead. A flat board lets the paint pool randomly and dry in patches; a steep board makes it run away.
Use the largest brush that fits the area.A big brush carries enough paint to cross the whole width without reloading, and reloading mid-stroke is where streaks come from. A flat wash brush or a large round both work.
Lay the first band across the top in one movement.One horizontal stroke, left to right, without lifting. A bead of paint will gather along the bottom edge — that bead is the whole mechanism.
Lay each subsequent band just overlapping the bead.Come back the other way, catching the bead so it is drawn down into the new stroke. Never leave a gap and never go back over a band you have already laid.
Reload without stopping.Dip and return to where you left off in one motion. If you hesitate, the bead starts to dry and the join will show permanently.
Lift the final bead off.At the bottom, squeeze the brush dry between finger and thumb or on a cloth, then touch it to the bead. It draws the surplus up. Left in place, it runs back into the wash and blooms.
Leave it absolutely alone to dry, flat.Lay the board down level and walk away. Every attempt to improve a drying wash makes it worse.

Tips

For a graded wash — dark at the top fading to light — do exactly the same thing but add clean water to the mix with each band. For the reverse, start with water and add pigment.
Some pigments granulate and settle into the paper texture, which makes a truly flat wash impossible with them. Ultramarine and many earth colours do this. It is beautiful and it is not a fault.
Paper that has not been stretched will cockle under a large wash, and the paint pools in the valleys. This is the main practical reason to stretch paper.
Practise on cheap paper. Ten flat washes in a row teaches the bead better than any explanation, and the tenth will be noticeably better than the first.

Common mistakes

Going back over a band to even it out — The band underneath is already setting. Brushing it again lifts pigment unevenly and leaves a permanent streak. One pass only.
Working with the board flat — Without gravity there is no bead, so each stroke dries on its own and every join shows.
Using a brush that is too small — It forces you to reload several times per band, and each reload is a potential break in the bead.
Mixing more paint halfway through — The wash dries while you mix, and the new mixture will not match. Mix generously at the start.

If it doesn't work

Horizontal stripes across the wash

Cause: The bead dried between bands — Fix: Work faster, tilt more, and use a bigger brush. On the existing wash, a thin even glaze of the same colour once fully dry will reduce the stripes considerably.

A dark line at the bottom of the wash

Cause: The final bead was left to dry in place — Fix: Lift it with a thirsty brush next time. On this one, soften it with a damp brush and blot once it is dry.

The wash dried lighter at the top

Cause: Pigment settling downhill, or the mix separating — Fix: Stir the mix before starting and again if it stands. Some heavy pigments will always do this — swap to a finer-grained one for large flat areas.

The paper buckled and the wash pooled

Cause: Unstretched paper, or paper too light for the amount of water — Fix: Stretch the paper, or use a heavier weight. Nothing about brush technique compensates for a cockled surface.

Questions people ask

Do I need a special wash brush?

A large flat brush — a hake or a wide synthetic flat — is convenient, but a large round holds more water and works just as well. Size matters far more than shape.

Why do my washes look better in cheap paint than expensive?

It is usually the opposite, but heavily granulating artist pigments do lay less flat than fine-ground student ones. If you want flatness, choose a non-granulating pigment.

How do I lay a wash around a complicated shape?

Either mask it first, or work with a smaller brush and accept slower progress — which means more risk of streaks. Masking fluid exists precisely for this situation.