Sunday, April 16, 2017

What is granulation?

Granulation, flocculation, sedimentary pigments, textured pigments, there are many terms used to describe the textured effects that some watercolors exhibit. As I regularly mention granulation, and it is one of my favorite watercolor properties, I thought I would explain the different terms here.

What are textured pigments?

Watercolors get their color from color pigments, tiny color particles that can be natural or synthetic. The term textured pigments simply refers to any pigment whose particles create a pattern or texture on the paper when dry.

There are granulating and flocculating pigments, as well as several different pigment properties that can cause a color to have a textured appearance.

What is granulation?

Granulation is the textured or grainy effect that is caused by pigment particles settling in the indentations of the paper. Granulation, as all textured effects, is more noticeable in juicy washes (when more water is used).

One example of a granulating color is Cobalt Blue, PB28.

Granulation - Cobalt Blue, PB28
© 2017 Anna C./See. Be. Draw.

Note that granulation may vary between brands. I am using Winsor & Newton Professional watercolors in these examples, unless noted otherwise.

What is flocculation?

Flocculation is the textured, speckled, effect that is caused by certain fine pigment particles that group themselves together on the paper and form a pattern mostly independent of the indentations of the paper. This phenomenon is usually caused by electrical effects as the particles become electrically charged and clump together.

One example of a flocculating color is French Ultramarine, PB29.

Flocculation - French Ultramarine, PB 29
© 2017 Anna C./See. Be. Draw.

Another example is Prussian Blue, PB27. If you look closely at this wash, you can see tiny black iron particles settling out from the color.

Prussian Blue, PB27
© 2017 Anna C./See. Be. Draw.

The pigment particles of Mars Black, PBk11, take the action one step further and literally start to move around as soon as you put your brush to paper. The swirls formed are easily visible!

Mars Black, PBk11
© 2017 Anna C./See. Be. Draw.

What are sedimentary pigments?

Sedimentary pigments are very heavy and/or very large pigment particles that sink in a water solution, especially noticeable on your palette or in your water jar.

Pigment particle size

Most pigments are manufactured in a range of particle sizes depending on the use of the pigment. Within each color is a range of pigment particle sizes, which means that both the average pigment particle size and the distribution of sizes also affect color properties.

The larger the pigment particle size, the more textured the resulting wash.

Among the largest pigment particles are cobalts, manganese, cerulean blue, iron oxides, and cadmiums.

Note that these colors may or may not be labeled granulating, but they may still be textured, especially when used with plenty of water.

Cobalt Blue, Cerulean Blue, Cobalt Turquoise Light, Cobalt Turquoise
© 2017 Anna C./See. Be. Draw.

Red iron oxides: Burnt Sienna, Venetian Red, Indian Red, Caput Mortuum Violet
© 2017 Anna C./See. Be. Draw.

Pigment particle weight

Specific gravity is the weight of the pigment in water and is independent of particle size. Heavy pigments have a specific gravity (much) heavier than water (which has a specific gravity of one) and therefore sink in water.

Among the heaviest pigment particles are chromiums, cadmiums, and cobalts. Note that the sedimentary qualities can vary between brands.

When pigments with a contrast in specific gravity are used together (heavier pigments together with lighter pigments), separation between pigments forms interesting textured effects on the paper.

Separation and texture

Some premixed colors contain one pigment that is granulating and one pigment that is not. In that case, you may notice a separation of pigments within that color, the granulating pigment creating a textured effect.

Premixed green with a granulating blue and a non-granulating yellow
(Prussian Green by Daniel Smith)
© 2017 Anna C./See. Be. Draw.

Similarly, if you mix a granulating color with a non-granulating color, you will get a beautifully textured effect!

Granulating colors mixed with non-granulating colors
© 2017 Anna C./See. Be. Draw.

In addition, two non-granulating colors that are mixed, either premixed in a tube or mixed directly on the paper, may separate on the paper causing a textured effect.

Two pre-mixed non-granulating greens
© 2017 Anna C./See. Be. Draw.

Smooth pigments and texture

All pigment particles group themselves together to some extent, something that is counteracted by additives to the paint. Particle clusters are called aggregates, whereas aggregate clusters are called agglomerates.  

In certain smooth pigments that are fully saturated, a contrast between these clusters or clumps create a textured effect despite being listed as non-granulating.

Smooth pigment that shows a textured effect
© 2017 Anna C./See. Be. Draw.

Can any pigment be made to look textured?

Well, I would say that, under the right conditions, it is possible to make several, although not all, non-granulating pigments to look textured to some degree. In fact, by using a textured watercolor paper such as a cold press or rough paper, watercolors by default get a textured look. 

Test it out for yourself by using the color first with plenty of water on a cold press or rough watercolor paper. Another option is to use the color almost completely saturated. In both cases, the color will almost completely fill the indentations and more color will be deposited there, giving it a more textured look.

Non-granulating, saturated color with a textured look
(Perylene Maroon by Daniel Smith)
© 2017 Anna C./See. Be. Draw.

If you want to learn more about pigment properties, check out Handprint's website, especially the pages on How watercolor paints are made, The material attributes of paints, and Guide to watercolor pigments.


Felicity Grace said...

Fascinating and informative post. I wondered why paints were reacting in a certain way and why I was struggling - now I understand! I tend to think only of granulating and non granulating but clearly there is so much more going on. I feel I need to get my watercolours out again!

Anna C. said...

Yes, once you dive into the world of watercolor properties you realize that there is so much more going on that is dependent on the watercolor properties. And to further complicate things, the properties may vary quite a bit from brand to brand. I have several colors in both W&N and DS and they are different both in terms of how the color itself looks, and what properties it exhibits. Yes, do get your watercolors out again in time for summer! Thanks for stopping by!