How to paint a wet-on-wet watercolour sky: step by step
The sky is often the first thing a watercolour beginner attempts — and also one of the first things that goes wrong. Paint dries too fast. Hard edges appear where you wanted soft ones. Colours go muddy in the middle. The paper buckles and the wash pools unevenly. It can be a discouraging introduction to a technique that, once understood, is one of the most enjoyable and satisfying in all of watercolour painting.
The wet-on-wet technique — where wet paint is applied to wet paper — is the key to painting skies that look soft, atmospheric, and alive. It is how most professional watercolourists approach sky painting, and it produces results that are very difficult to achieve any other way. This guide walks through the technique step by step, explains what to do when things go wrong, and gives you the foundation to paint convincing skies in any weather and any light.
What is wet-on-wet watercolour?
Wet-on-wet (sometimes written wet-into-wet) simply means applying wet paint to paper that is already wet. When you do this, the paint spreads and bleeds into the damp surface, creating soft, diffuse edges with no hard lines. This is the opposite of wet-on-dry, where wet paint applied to dry paper creates crisp, defined marks.
The soft edges produced by wet-on-wet are what make it ideal for skies. Clouds in nature have edges that fade gently into the surrounding blue rather than cutting sharply against it, and wet-on-wet is the most natural way to capture that quality. The technique also allows colours to blend and merge on the paper in ways that look organic and spontaneous — and that you could not achieve by mixing the colours together on a palette first.
The trade-off is control. Wet-on-wet is less predictable than wet-on-dry, and the results depend heavily on how wet the paper is, how much water is in your brush, and how quickly you work. This unpredictability is part of what makes watercolour exciting — but it does mean that practice and observation are essential.
What you will need
Before you start, gather everything you need within easy reach. Wet-on-wet requires you to work quickly once the paper is wetted, and stopping to find a brush or mix a colour will cost you precious time.
You will need a sheet of 300gsm cold press watercolour paper — Saunders Waterford, Fabriano Classico 5, or Bockingford all work well for this technique. Lighter paper will buckle badly when wetted. A watercolour block is ideal as it holds the paper flat without needing to tape or stretch it.
For brushes, a large flat or mop brush for wetting the paper and laying in broad washes, and a medium round brush (size 8 or 10) for adding colour and shaping clouds. A small round brush for any detail work once the sky is dry.
For colours, a simple sky palette of three colours covers most situations beautifully: French Ultramarine for the upper sky, Cerulean Blue for the lower sky and horizon, and Raw Sienna or Yellow Ochre for the warm glow near the horizon. A neutral grey mixed from Ultramarine and Burnt Umber or Burnt Sienna is useful for cloud shadows. You do not need many colours — restraint is a virtue in sky painting.
A spray bottle of clean water, a jar of clean water, and kitchen roll or a clean cloth for lifting and correcting complete the kit.
Mix your colours in advance in generous puddles on your palette before wetting the paper. Running out of a mixed colour mid-wash is one of the most common causes of ruined skies — always mix more than you think you will need.
Step by step: a simple blue sky with clouds
Step 1: Prepare the paper
Place your paper on a board or use a watercolour block. If using loose paper, tape all four edges to the board with masking tape or gummed tape to prevent buckling.
Tilt the board at a slight angle — around 15 to 30 degrees. This encourages washes to flow gently downward, which helps create natural gradations and prevents paint from pooling in the middle of the sky.
Step 2: Wet the paper
Using your large flat or mop brush loaded with clean water, wet the entire sky area evenly. Work in overlapping strokes, covering the surface systematically so no dry patches remain. The paper should have an even, dull sheen — like a slightly misted window. If you can see pools or puddles of standing water, blot gently with kitchen roll. If the surface looks completely dry in places, go over those areas again.
The right level of wetness is crucial. Too wet and your colours will flood uncontrollably; too dry and you will get hard edges where you do not want them. The dull sheen — not glossy, not dry — is the sweet spot you are aiming for.
Step 3: Lay in the sky colour
Working quickly, load your large brush with your pre-mixed French Ultramarine and begin laying in the upper sky. Use broad, confident horizontal strokes across the top of the paper, working downward. The colour will spread and soften immediately on the wet surface — this is exactly what you want.
As you move down toward the horizon, switch to your Cerulean Blue and continue the wash, allowing the two blues to blend naturally where they meet in the middle. The sky in nature graduates from a deeper, darker blue overhead to a paler, slightly greener blue toward the horizon, and this two-colour approach captures that quality simply and convincingly.
Leave areas of untouched damp paper where you want white or light clouds. These reserved whites are your brightest lights and are impossible to reclaim once painted over, so err on the side of leaving too much white rather than too little at this stage.
Step 4: Add warmth near the horizon
While the paper is still wet, load your brush with a very dilute wash of Raw Sienna or Yellow Ochre and touch it lightly into the area just above the horizon line. The warm tone will bleed gently into the surrounding blue, creating the soft, hazy warmth that skies in the UK often show near the horizon — particularly in morning or evening light.
Use very little paint here. The horizon warmth should be subtle, a suggestion rather than a statement.
Step 5: Add cloud shadows
Mix a soft grey from French Ultramarine and Burnt Umber — lean it slightly toward blue for a cool, overcast feel, or slightly toward brown for warmer, sunlit clouds. This mixture should be dilute but noticeable.
While the paper is still damp, use your medium round brush to paint the shadowed undersides of your clouds. Touch the brush to the paper and allow the colour to spread and feather naturally into the damp surface. Do not drag or scrub — simply touch and lift. The wet paper will do the work of softening the edges for you.
The shadows sit at the bottom of cloud forms, where the cloud is thickest and the sunlight cannot penetrate. Keep the upper edges of your clouds light and the lower edges slightly darker, and the forms will immediately look three-dimensional.
Step 6: Stop and let it dry
This is the hardest step for most beginners. Once the sky is laid in, put your brush down and leave it alone.
The temptation to keep working, adjusting, and correcting is strong — but wet-on-wet watercolour rewards restraint. Every additional brushstroke risks disturbing the drying surface and creating unwanted hard edges or blooms. The paint will continue to move and settle as it dries, and the finished result is often more beautiful than it looked when wet.
Allow the sky to dry completely — at least 20 to 30 minutes, longer in humid conditions — before adding any further detail. A hairdryer can be used to speed drying but keep it moving and hold it at a distance to avoid forcing the paint into unnatural patterns.
What is the sheen method and why does it matter?
Experienced watercolourists talk about watching the sheen of the paper as a guide to when it is safe to add more paint or detail.
When paper is first wetted it has a bright, glossy sheen. At this stage the surface is very wet and paint will spread widely and unpredictably. As the paper dries, the sheen dulls — this is the ideal moment to add paint for loose, soft-edged marks. When the sheen disappears entirely and the paper looks matte, the surface is almost dry. Adding wet paint at this stage creates the dreaded cauliflower bloom — a hard, frilly edge where the new water forces the drying pigment aside. This is not always unwanted (blooms can look beautiful in the right context) but in a sky they are usually a nuisance.
Learning to read the sheen is one of the most important skills in wet-on-wet watercolour. It takes practice but once you have it, your control of the technique improves dramatically.
Common problems and how to fix them
Hard edges appearing where you wanted soft ones. This almost always means the paper was too dry when you added the paint. The solution is to work faster, pre-wet a larger area, or work on smaller sections of sky at a time.
Colours going muddy in the middle. Usually caused by overworking — too many brushstrokes back and forth across the same area while the paint is drying. Mix your colours cleanly on the palette before applying them, and resist the urge to push paint around on the paper.
Blooms and cauliflower edges. Caused by adding wet paint or water to a surface that is partially dry. Watch the sheen carefully, and if the paper is losing its sheen, stop adding paint and let it dry fully before continuing.
The paper buckling. Almost always a weight issue — use 300gsm paper as a minimum. If using loose paper, tape all four edges before you start. A watercolour block eliminates this problem entirely.
The sky drying too fast. Very common in warm or dry conditions. Work on smaller sections at a time, use a spray bottle to re-wet areas that are drying too quickly, or add a small amount of retarder medium to your water jar to slow evaporation slightly.
White clouds disappearing. Once you have painted over them, white areas are very difficult to recover cleanly. You can lift paint from a still-wet surface using a clean, almost-dry brush or a piece of kitchen roll, but prevention is always better. Reserve your whites deliberately and leave more than you think you need.
Colour choices for different sky conditions
The three-colour palette described above — French Ultramarine, Cerulean, Raw Sienna — is a reliable starting point for most blue-sky conditions. But different weather and light call for different approaches.
For overcast or stormy skies, lean heavily on Ultramarine mixed with Burnt Umber or Burnt Sienna for a range of warm and cool greys. Vary the proportion of each to get variety across the sky — cooler greys overhead, warmer greys near the horizon.
For sunset and sunrise, introduce Cadmium Orange, Quinacridone Magenta, or Permanent Rose alongside the yellows and blues. Keep the colours wet enough to blend freely and work quickly before the gradations dry into hard bands.
For early morning mist, a very pale wash of Raw Sienna or Naples Yellow across the whole sky area, followed by the palest possible blue in the upper sky, captures the soft, milky quality of morning light beautifully.
For a heavy, rain-laden sky, a single large wash of mixed grey — Ultramarine and Burnt Umber in roughly equal parts — applied quickly and confidently across the whole sky can be extraordinarily powerful. Some of the most dramatic watercolour skies are painted in just one or two washes.
Frequently asked questions about painting watercolour skies
Do I need to wet the whole paper or just the sky area? For most sky-and-landscape compositions, wet only the sky area and leave the land below dry. This gives you soft edges in the sky while keeping the horizon line and foreground crisp. If you want the sky and land to bleed together — for a misty, atmospheric effect — wet the whole paper.
How do I keep my clouds white? Simply leave those areas of paper unpainted. Watercolour is a transparent medium and the white of the paper is your brightest light — you cannot add white paint effectively over a wash. Plan where your clouds will be before you start and leave those areas dry when wetting the paper. If you want to protect very precise cloud shapes, masking fluid applied before wetting will preserve them, though the edges will be harder.
My sky always looks flat — what am I doing wrong? Flat skies usually lack tonal variation — they are one even wash of the same colour at the same strength. Real skies have light and dark areas, warm and cool passages, and a gradation from deep overhead to pale at the horizon. Introduce at least two blues and vary the strength of your wash across the sky. Adding cloud shadows, even very subtle ones, immediately gives the sky depth.
Can I go back and fix a sky once it has dried? To some extent. You can re-wet a dried sky and add further washes of colour or shadow, though the result is never quite as fresh as a sky painted in one go. You can also lift dried paint with a damp brush or a stiff-bristled brush for textured cloud effects. Accept that some skies will not work — in watercolour, knowing when to start again is as important as knowing how to fix things.
What size brush should I use for sky painting? Bigger than you think. Most beginners use brushes that are too small for covering large areas quickly, which forces them to make too many strokes and overwork the wash. A size 12 round or a large flat wash brush for the initial wet application and broad colour washes, with a size 8 or 10 for cloud shadows and softer details, covers most situations.
Is cold press or hot press paper better for sky painting? Cold press is the better choice for most sky painting. Its texture helps distribute water evenly and gives washes a natural, slightly varied quality that suits atmospheric subjects. Hot press is smoother and better for fine detail — less well suited to the loose, wet work of sky painting.
Shop watercolour supplies at Craft and Canvas
We stock everything you need for wet-on-wet sky painting at Craft and Canvas in Hebden Bridge and online at craftandcanvas.co.uk — including Saunders Waterford, Fabriano Classico 5, and Bockingford watercolour papers, Wallace Seymour and Winsor & Newton watercolour paints, and a full range of brushes and mediums. If you are not sure which papers or colours to start with, come in and ask us.
Craft and Canvas | 3 Carlton Street, Hebden Bridge, HX7 8ER | craftandcanvas.co.uk