What is granulation in watercolour? Why does it happen?

Have you ever painted a wash and found that it looks a bit blotchy and granular? That is the phenomena of granulation – loved and hated in possibly equal measures by watercolourists. I am a big fan, as I think it adds interesting marks and textures which are unachievable in any other way.

The clouds of smoke here rely on granulation for their texture

Granulating paints are big business too. Daniel Smith builds its business on the unique granulating properties of its paints. Schmincke is trying to get a slice of the action with its new range of ‘Super granulating watercolours’, then there are the less well known Van Gogh Dusk colours from Royal Talens.

So let’s find out what granulation is, why it occurs and how we might encourage or discourage it….

What is granulation?

It is simply when the pigment gets deposited in an uneven way in the troughs of the paper surface. This happens with bigger pigment particles, especially those of an uneven size. It is a little different from the process of flocculation, where there is a mutual attraction between the particle which causes them to clump together and settle out of the liquid. Don’t be bothered by the diffence – the effect is much the same.

Mars Black PBK 11 has strong granulating properties

What causes granulation?

There are three causes – the pigment, the paper and the water:

Pigment – certain pigments are prone to granulation – French Ultramarine, true Earth Colours, Cobalt pigments and some blacks especially Mars Black (PBk11). Manmade, pigments which are often bright and transparent, such as the phthalos and quinacridones, will not granulate due to the fine nature of their particle size.

Paper – the clumps or particles need somewhere to settle, so the effect is far greater on a Not/cold press paper, than it is on a Hot Press. The effect is even greater on a rough paper.

Water – the particles need to be able to move around in the water, in order to then settle in the troughs. So the more water you use, the greater the granulation. Minerals in water will also encourage the effect, so those living in hard water areas are at an advantage.

Encouraging maximum granulation

Understanding this immediately tells us that to encourage granulation we need to choose our pigments with care, use a rougher paper, use plenty of water with a high mineral content and also, leave the painting alone, so the particles can settle out. The opposite of these, will eliminate granulation. You can use a granulating medium (Winsor and Newton’s is the best known). I’ll cover this in a future blog.

Experimenting with granulating mixes

Looking at the pigment content of mixes such as Daniel Smith Lunar Blue, I can see that Mars Black has been mixed with phthalo blue and this got me to thinking whether Mars Black mixed with other bright fine non-granulating colours would also produce beautiful granulating mixes. The good news is that it does!

Some of my experiments adding fine bright pigments to PBk11

If you would like to see the results of my experiments, please go to this film on YouTube: https://youtu.be/hx6L-CkEZdM I was really pleased with many of the results (though not all). I will not be buying Lunar Black anytime soon!

Home made Lunar Blue

2 thoughts on “What is granulation in watercolour? Why does it happen?”

    1. Yes, do! The granulation is fab. I deliberately got a cheapish Mars Black (the Turner one), rather than DS or W&N and you can see the granulation is beautiful.

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