Wednesday, June 25, 2008

Colour - a materials perspective #1 - pigments and dyes

Pigmenti per artisti
- the front window of the pigment shop in Venice

copyright Katherine Tyrrell

This post provides a materials perspective on colour for artists and a basic overview of pigments and dyes. Pigments and dyes are a prime component of the colour used by artists - but
  • Where do they come from?
  • Which are 'old' colours and which are new?
  • What or who creates them?
What materials create colour?

Colour in paint comes from pigments and dyes. All media – oils, watercolours, acrylics, pastels and coloured pencils – are derived from the same pigments and dyes. What actually varies between different media is the vehicle used to bind the pigment together.

Some pigments and dyes have been around for a very long time and some are modern and the result of recent manufacture. Basic colour knowledge relating to materials covers an elementary understanding of:
  • What are organic and inorganic pigments and dyes and where do they come from
  • The relationship between pigments and dyes and lightfastness
  • ‘Old’ pigments still in use – and those which have been replaced
  • ‘New’ pigments created in the laboratories – and why they are a good thing
I can see this will take more than one post so first. I'm going to explain the basics about pigments and dyes today.

What are pigments and dyes? (Definitions)

What is pigment and what is a dye? How does a pigment differ from a dye?

At a basic level:
  • pigments
    • do not dissolve in water and may be opaque.
    • Even when ground down, particle sizes are much larger than a water molecule.
    • Pigments are used by artists.
  • dyes
    • dissolve in water,
    • are always transparent and
    • can bind permanently to all porous materials.
    • Dyes are mostly used in industry.
Here are some different definitions that I've collected.
A pigment is a material that changes the color of light it reflects as the result of selective color absorption.......permanence and stability are desirable properties. Pigments that are not permanent are called fugitive. Fugitive pigments fade over time, or with exposure to light, while some eventually blacken.
Wikipedia - pigment

The colouring agent in drawing and painting media. originally from natural plant and mineral sources, most pigments are now synthentic. Pigment also refers tp pure colour in powder form
Artists Colour Manual"

Pigments are powders that are in a binder such as acrylic or oil which covers or adheres to a surface.
"Colour"

pigment
noun 1 any insoluble colouring matter that is used in suspension in water, oil or other liquids to give colour to paint, paper, etc. Compare dye. 2 a coloured substance that occurs naturally in living tissues, eg the red blood pigment haemoglobin, or chlorophyll in the leaves of green plants. verb (pigmented, pigmenting) to colour something with pigment; to dye or stain. pigmentary or pigmented adj.
ETYMOLOGY:
14c: from Latin pigmentum, from pigere or pingere to paint.
Chambers Dictionary

You use dyes to dye to produce a dyed colour! Confused? See below for an explanation....
dye verb (dyed, dyeing) tr & intr to colour or stain something, or undergo colouring or staining often permanently. noun 1 a coloured substance, either natural or synthetic, that is used in solution to impart colour to another material, eg paper, textiles, leather, hair. Compare pigment. 2 the solution used for dyeing. 3 the colour produced by dyeing. dyable or dyeable adj. dyer noun someone who dyes cloth, etc, especially as a business.
ETYMOLOGY:
Anglo-Saxon deagian.
Chambers Dictionary


Dye: A colouring agent that dissolves in water, used for colouring fabrics. Dyes are also used to colour white powder to produc 'pigment lakes' and 'pinks'. .....
Lake: The pigment colour produced by dyeing a white inorganic material such as gypsum or chalk with organi colouring matter through the use of a mordant
"Artists Colour Manual"

Dyes are pigments that are dissolved and absorbed in a fluid
"Colour"

Organic and Inorganic; natural and synthetic

Pigments are either organic or inorganic.
This means whether or not the molecules contain carbon - organic pigments contain carbon.

This historical differentiation was based on a notion that organic means coming from things which were living and inorganic means it wasn't synthesized from a life force.

Today, there is a more defined separation between what is natural (from a living organism); what is synthetic (manufactured through a chemical process) and what is inorganic (not from a life force)

Rubia Tinctorum - Common Madder
Wikimedia

Today there are:
  • natural organic pigments/dyes - these are pigments/dyes extracted from natural (animal and vegetable) sources and living organisms e.g. derivatives of madder or cochineal. They are chopped, ground, boiled and dried to extract the pigment powders. They have a tendency to fade.
  • synthetic organic pigments/dyes - these are pigments/dyes that are manufactured as organic compounds e.g. alizarin crimson (a synthetic replacement for madder) and all the quinacridone colours (which are organic compounds and include the modern synthetic replacement for alizarin crimson because of concerns about the latter's weaknesses in relation to colour fastness)
  • inorganic pigments/dyes - these are derived from naturally occurring earth colours (eg ochres and iron oxides ), metal compounds, minerals (e.g. cobalt) and clays.
I'm still trying to find a website which defines all colours by whether they are organic or inorganic, natural or synthetic.
There are a number of other websites which provide excellent information about pigments - for example
How do pigments behave?

Not all pigments behave in the same way e.g. pigments can dry at different rates. Consequently it is worth trying to understand a little bit more about the characteristics of different pigments. (This is different from understanding the difference between different paints.)

The basic characteristics of a pigment vary as to:
  • colour bias
  • granulation/dispersion /sedimentation (try the Handprint sedimentation test )
  • toxicity
  • tinting strength
  • staining and bleeding
  • transparency or opacity
  • Resistance to alkalis and acids
  • Reactions and interactions between pigments
  • drying rate
  • lightfastness
Binders and other ingredients in art media

More from Arcobaleno Pigmenti de Nube Massimo - the pigment shop in Venice (see Venice - a resource for artists for a map of where it is)
copyright Katherine Tyrrell

Differences between media and between different brands of one medium are significantly influenced by the different formulae used by different manufacturers and the extent to which they vary substances used to bind the pigment into the medium.

Pigments are used for coloring paint, ink, plastic, fabric, cosmetics, food and other materials. Most pigments used in manufacturing and the visual arts are dry colourants, usually ground into a fine powder. This powder is added to a vehicle (or matrix), a relatively neutral or colorless material that acts as a binder.
Wikipedia - pigment
Art media normally start with two principal ingredients:
  • colourant, commonly pigment (organic or inorganic);
  • binder, the substance that holds the pigment in suspension and fixes the pigment to the painting surface
Some media, most often paint, also includes or needs to be combined with two more ingredients:
  • additives, substances that alter the viscosity, hiding, durability or color of the pigment and vehicle mixture; and
  • solvent, the substance used to thin or dilute the paint for application and that evaporates when the paint hardens or dries.

The main reasons why people like a particular art medium are due to:

  • quality of the pigment used (eg how finely it is ground - is it gritty or not?)
  • the nature of the binders and additives used (eg how well the paint flows or gives up its pigment)
  • the ratio of binders and fillers to pigment (the pigment load)
The binders and fillers added to pigments vary in terms of how they affect, for example, the saturation or lightness of a colour. Each has its own unique way of reflecting or absorbing colour and thus determine the final spectrum of colour available. Binders surround pigment particles and control how the pigment reacts to light and the environment. The nature of the pigment can dictate which binder produces the best result.
  • Dry binders include: wax, oil, clay/kaolin, graphite (Carbon mixed with clay)
  • Liquid binders include: water, egg yolk+water, liquid, linseed oil, beeswax, acrylic polymer, gum arabic, oil, milk-derived polymer, powdered glass.
Using high quality materials slows down the response to atmospheric conditions.

I'm aiming to produce a chart at some point showing how binders combine with pigments to produce different art media.

Permanence and lightfastness

In the last 200 years, the range of pigments and colours has increased but, more importantly, so has the lightfastness. This will be covered when I look at the classification of colour.

Colourmen

Prior to the advent of tube paint, most paints were made up by people called Colourmen who sold premixed paint in pigs bladders.

Pere Tanguey, painted three times by Van Gogh (see right), was one such colourman who supplied a number of painters in Paris at the end of the nineteenth century.

This is a link to the Winsor & Newton Colourman's Manuscript Archive Project: Page-Image Database of Historic Recipes for Paint Making

LEARNING POINTS

I've decided it might be useful to try and summarise what can be concluded from the overview

  • all colours come from pigments or dyes;
  • pigments and dyes come from a number of different sources
  • a pigment is a material which can provide colour but which does not dissolve in water
  • a dye is a pigment ground down to very fine particles which can impart colour when suspended in a solution or medium
  • pigments do not all behave in the same way - because they come from different sources
  • what makes paint vary can be the nature of the pigment - but it can also be the binder or filler used to make the medium. In other words it's not just about the pigment load.
Tomorrow - more about the art materials perspective on colour.

Bibliography:
Links:

The Making A Mark Project on Colour - previous posts

Resources for Artists information sites created by makingamark

1 comment:

Soli said...

THis is great so far. A useful resource! Thank you

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