Granulation is the visible, textured pattern some watercolour pigments make as a wash dries. It is a material tendency, not a flaw, and one that a painter can encourage, soften or avoid.
At a glance
Granulation begins with the pigment. Paper surface and handling affect how clearly it appears, but a smooth pigment will not suddenly become strongly granulating because the paper is rough.
Textured paper makes it easier to see. Rough paper shows the strongest effect. Cold press offers a more controlled version. Hot press usually reduces it.
French Ultramarine, PB29, is a useful starting point. It is a widely used pigment that often granulates, although the strength varies by maker, paper and wash.
Water and drying speed matter. A wetter wash that dries slowly tends to show more separation than a drier wash, but paper and environment also affect the result.
You can reduce the effect. Choose smoother pigments, use a smoother surface, and test a less watery wash before committing to a larger passage.
What actually causes granulation
Granulation happens as pigment particles move and settle while the water in a wash evaporates. Sedimentation plays a part, particularly with pigments whose particles are relatively heavy. Flocculation matters too: particles can gather into small, irregular groups rather than staying evenly dispersed in the binder.
Particle size and density, together with the way particles interact in the binder, influence the result. Inorganic pigments, whether mined or manufactured, often have particle characteristics that make granulation more likely. Organic pigments often disperse more evenly. These are broad tendencies rather than rules. Milling, dispersion, pigment concentration and paper surface mean two paints with the same Colour Index code can still look different in a wash.
The familiar contrast is French Ultramarine, PB29, beside a phthalo blue from the PB15 family. The ultramarine often settles into a textured pattern. The phthalo blue usually dries more evenly. Neither behaviour is better. They simply serve different purposes.
For the full explanation of Colour Index codes, see what watercolour pigment codes actually mean. The code identifies the pigment in the tube, but it does not guarantee identical handling between makers.
Which pigments tend to granulate
Ultramarines, cobalt colours and many earth colours are the families painters most often associate with granulation. PB29 French Ultramarine is a practical place to start because it gives a visible result in many ranges without being difficult to use. Cerulean colours, commonly labelled PB35 or PB36, often granulate more strongly, but colour names are not enough: check the pigment code because manufacturers use Cerulean Blue for more than one formulation.
Cobalt Blue, PB28, and Ultramarine Violet, PV15, often show granulation to varying degrees. Several natural earth colours can also settle visibly on textured paper, although their handling is covered in more detail in the guide to earth pigments. Yellow Ochre, PY43, and iron oxide blacks such as Mars Black may show texture, but the effect varies between makers and papers.
By contrast, the phthalo blues, PB15 family, and quinacridones such as PV19 usually dry more evenly. Smooth pigments are useful when you want a flat wash, a clean mix, or a passage with little surface texture. Test the actual tubes you use rather than treating a pigment name as a promise.
How paper surface affects watercolour granulation
Paper surface does not create granulation, but it determines how much of it the eye can see. A rough surface has deeper texture, giving settling particles more visible places to collect. The result can be pronounced and irregular.
Cold press has enough texture to show granulation while keeping a wash relatively easy to control. It is where many painters first notice the effect and often the most useful surface for learning how a particular pigment behaves.
Hot press paper is smoother. A granulating pigment may still show some separation, but the texture is usually much less obvious. Weight and surface are separate properties: rough, cold press and hot press papers come in more than one weight.
Reducing or avoiding granulation
If you need a flatter wash, begin with a smoother pigment in the same colour position. A phthalo blue, for example, is usually a better starting point than ultramarine when an even blue passage matters more than surface texture.
Paper is the next lever. Hot press reduces the visible effect, while a smoother cold press sheet can be a useful compromise when you still want some absorbency. On the same paper, a less watery wash and faster drying conditions can reduce separation, although neither gives an identical result every time.
Avoid treating the wash as a correction exercise. Reworking a drying wash can create other marks rather than simply removing granulation. Make two small test swatches first, one wetter and one drier, then choose the result that suits the passage.
Practical test
A simple test card
- Choose one or two pigments and one paper.
- Paint one wash with a generous water load and a second with less water.
- Tilt the board slightly, then leave both swatches to dry undisturbed.
- Compare the results on the same paper and note which wash showed more texture.
The point is not to make the most dramatic possible effect. It is to learn what your own tubes do on the paper you use.
Using granulation deliberately in skies and shadows
Granulation adds visible texture to skies, shadows and passages where an uneven surface can suggest atmosphere or distance. A wash of PB29 can give a sky a broken, weathered quality, while a flat wash of a smoother pigment will read more evenly.
A shadow mixed from a granulating blue and an earth colour can carry more movement than a smooth mixture. The result depends on the proportions, paper, water load and the particular paints involved, so use the test card before relying on it in a finished piece.
The useful technique is restraint. Apply the wash with a clear intention, then allow it to dry without repeatedly trying to even it out. Detailed wash and sky technique belongs in the technique guides; here, the important point is that granulation is part of the material decision.
Mixing granulating and smooth pigments
Mixing a granulating pigment with a smoother one can produce a wash in which texture and a more even colour coexist. PB29 French Ultramarine and PV19 Quinacridone make a useful example: the exact result will vary, but the blue often settles more visibly while the quinacridone contributes a smoother, warmer note.
The same pigment can behave differently in a mixture than it does alone. Other pigments, the water ratio, the paper and drying speed all influence the result. Granulation tests are easier to interpret when you know what is in each paint, which is one reason single-pigment watercolours are useful for a working palette.
The practical verdict
Granulation is a material property worth understanding before it becomes an effect you try to force. Choose a pigment because its texture suits the passage, choose a paper that allows that texture to show, and test the combination before a larger wash.
French Ultramarine on cold press is a good first test, but it is only a starting point. The useful knowledge is how your own pigments, water load and paper work together.