Understanding pigments: the nitty gritty on colour

Raw pigments

Pigment, not what you would get if you made a pig out of cement, but it is instead the light reflecting particles used as the colourant in paints. As long as the human race has existed we have in some form or another been using pigments for decorative purposes. The ways we obtain these colours are as numerous as they are ingenious. So we ask ourselves, why is it important to understand pigment as artists and how can we apply that knowledge to better inform our creative decisions? 

Raw pigments in their milled, powdered form. Ready for mixing with a binder to make paint.

What do we mean when we say pigment?

So what constitutes a pigment specifically and what differentiates it from a dye?
A pigment is a coloured material that is finely ground, and is nearly insoluble in water unlike a dye. They are extracted from various minerals and organic materials or are synthesised artificially by chemists.

     The main quality that distinguishes a pigment from a dye is that pigments are insoluble in the medium (gum arabic, acrylic polymer, linseed oil) they are combined with. That is to say they do not dissolve and bond with their solvent on a chemical level whereas a dye will. This is why paint is a suspension scientifically speaking. The pigment is dispersed in its medium and will separate from the medium if left to settle over time. Dyes do not separate from their solvent medium and are called a solution. You can see this phenomenon in acrylic inks when the pigment sinks to the bottom of the bottle if the ink has been left standing for a while.

     Pigments have a high resistance to fading in light due to them being tiny particles of solids that are deposited onto the surface they are used on. Pigments come in a variety of opacities and the pigment density present in a colour will affect the overall “coverage” of a paint.

 

Raw lapis lazuli, as a metamorphic rock it is comprised of multiple minerals which have been pressed together under intense pressure and heat. Note the veins of yellow pyrite (fools gold) which are one of the many excess materials which must be filtered from the blue azurite in order to obtain the blue pigment use in traditional ultramarine.

Throughout history we have encountered a boggling number of naturally occurring materials which we have rendered into pigments. From iron rich clays of Italy which provide us with sienna and umber pigments, to the lapis mines of Afghanistan that provide the blue lazulite stone that traditional ultramarine pigment is composed of. Where the cost of such natural materials has become prohibitively expensive, we have turned to chemists to synthesise artificial pigments which can match the vibrancy and tonal qualities of these scarce materials.

     Some artists scoff at this practice but thanks to the efforts of colour scientists we have made acquiring colours more affordable and much safer. The history of art has been fraught with colours such as Paris green for example, which is a beautiful emerald green derived from the highly toxic element arsenic.

 

An antique tin of lead white paint intended for decorating. Lead paints are highly regulated in Europe.

In place of expensive or poisonous pigments we have derived alternative pigments such as french ultramarine, an artificial equivalent for the traditional ultramarine that is derived from lapis lazuli. This synthetic blue pigment was made by German chemist Christian Gmelin in 1828 by baking kaolinite, sodium carbonate and sulphur in a kiln.
     Today pigmentation is still a hotly debated topic amongst artists and colour chemists over longevity, colour stability, affordability, sustainability and even ethics of the pigments available. Manufacturer of fine oil paints and other colours Michael Harding for example seek to provide pigment of the highest quality available, and are also keen to ensure their pigments are obtained ethically and responsibly.

 

A question of quality and quantity.

A selection of ultramarine paints. Each will be slightly different.

The quality of paint also decides the pigments you will be painting with and putting on your palette. As previously stated there are pigments which command high prices due to their scare nature or the difficulty in acquiring them. Because of this you will find most paint manufacturers will have two main ranges of paint in any medium, these being professional or artist quality and student quality.
     Student quality paints will use synthetic pigments and the more inexpensive genuine ones as well. What you will find in place of genuine pigments like cadmium will be “hues”, the best approximation of the genuine article put forth by the paint manufacturer. Whenever you see a colour like “Cobalt Blue Hue” it means there will not be any actual cobalt pigment in the paint, and instead a replacement pigment or pigments to give the best match.
     Student paints will also be bulked out with extenders and contain less pigment in their composition, which leads to less vibrant colours and inferior colour mixing compared to higher quality paints. That being said many artists will use student quality paints for bulk colour when required due to their cost efficiency.
     Artist quality paints on the other hand feature both a higher pigment load, genuine pigments and a wider range of colours. Something worth noting is that these ranges will still often include hues amongst their selection of colours. The key difference is that the amount of those pigments used is substantially higher in artist paints and a lot less filler, if any, will be used to extend the colour. This means they mix with a higher clarity than student quality colours in comparison.
     Professional grade paints are often divided into price bands that reflect the cost of the pigment used in their creation. This usually takes the form of a numerical or alphabetical affectation such as “series 1”, with the paint getting more expensive the higher the number. Sometimes letters are used in place of numbers much in the same way. This means cheaper colours will be on the low end and more expensive ones will be on the high end, which makes it easier to understand the difference in cost between tubes.
     This makes it easier to understand the price difference between brands, their respective ranges and can help you budget your paint requirements accordingly before diving in.

Getting hands on with pigments.

Pots of Sennelier Dry Pigment, each is milled to a fine powder and sold by weight.

If you are intrigued by the premise of mixing your own paints from raw materials then you will be pleased to know that Sennelier offers a full range of artist quality raw pigments. 
     These dry pigments come ready milled to a fine powder, and can be used dry or mixed with a binder to create paint. Sennelier provides a number of binders which include acrylic, oil, watercolour and even tempera for traditional egg yolk based painting techniques.
     Raw pigments themselves can be used without a binder in their powdered form, much like you would use pastels to create soft tonal effects. Pigments are also sometimes used for weathering techniques where patches of dried pigments are applied selectively to areas of a painting, sculpture or model to mimic the look of dried dirt, dust, rust and verdigris just to give a few examples.
     Due to their powdered form they can be quite dusty and we would advise wearing a dust mask when handling them, as it is not a great idea to be inhaling pigment dust. Whilst most pigments sold commercially are non-toxic, we advise you to check all the pigments you are using and ensure you have the proper personal protective equipment and handle them responsibly.
 
Freshly milled oil paint produced by Winsor & Newton. They have refined their paint making skills over nearly 2 centuries of working with artists.

In summary we hope that this exploration of what pigments are exactly and how they are used in paint has given you a better understanding of the materials you use. Understanding how pigments are physically present within a medium, how the pigments chosen can affect colour mixing, the cost and quality of pigments and the invention of synthetic alternatives for the incredibly expensive genuine and how that impacts the quality of paints that are produced, and in turn how that will inform your own painting choices.
Pigments are the link between the chemistry of science and the expression of art and we encourage you to dig deeper into the history of pigments, painting and colour for yourself if you have found this article has piqued your interest. 

Ben Platt
Ben Platt


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