What are artist mediums?

The primary meaning of “medium” in portraits is the type of ‘paint’ used to produce the painting.

However, the medium can extend beyond paint to cover pencil, crayon, pastels, ink, computer generated art, fabrics and many other types of exotic materials.

For the sake of this blog, I will concentrate on the paint mediums that you are most likely to come across if you are considering commissioning a portrait painting.

Each portrait medium is usually associated with a specific surface that it is used on, so these will also considered alongside the paint classifications.

It will help if we first examine the composition of all artist paints, so that the differences can be more easily explained. Artists paints consist of:

Pigments -

These are the powdered elements that provide the colour. They have been known about and used for hundreds of thousands of years.

Initially they were naturally occurring oxides and ochres (clays and earth) that were ground into a powder. Over time other pigments were obtained from plants, insects, animal waste etc. to give a wider range of available colours.

Some colours of pigment were more rare and as a result, were very expensive (i.e. blues and purples) however, with the advent of the industrial revolution, synthetic pigments became available to give the full range of colours we have today.

A solution in which the pigments are dissolved -

This is what classifies the type of medium and has a major impact on the final appearance of the painting. Its purpose is to hold the pigment in suspension in a form that allows it to be applied.

A binder -

This is added for 2 reasons, firstly to help the solution keep the pigment in suspension, but secondly to supplement the expensive pigments with a cheaper colouring agent. Expensive paints will have a higher pigment to binder ratio than cheaper paints.

Other ‘agents’ -

which affect the feel and texture of the paint or it’s drying time, either speeding it up or slowing it down so that different painting techniques can be used.

The common portrait media paints tend to be oils, acrylics and watercolour, so I will concentrate on them. As listed above, the major difference is in the solution which holds the pigments in suspension, so let us examine typical solutions and the effect they have on the portrait and it’s production.

A.) Oil Paints -

The oils used are linseed oil, safflower, walnut or poppy seed oil. Linseed is the most common, but has the drawback that it does tend to yellow over time. The other oils do not yellow as much, if at all, but tend to take longer to dry and do not provide such a hard finish.

Oil paints do give a more lustrous look with beautiful colours. Due to their longer drying times, they can be ‘worked’ by the artist after they are applied, allowing them to be blended more easily resulting in more natural transitions between colours and tones (shades of dark and light). If there is a drawback to oils, it is the drying /hardening time. The process takes a long time and as a result, a protective varnish coat cannot be applied for many months.

The process of applying the paint is also quite prescriptive as thicker layers of paint take longer to dry than thin ones, and applying a thin layer on top of a thick one can lead to cracking of the thin layer as the thick one settles. For the artist there can be an issue with the solvents used to clean the brushes and thin the paint.

Most of the traditional solvents are classed as hazardous, however a relatively new type of oil paint overcomes these issues. They are referred to as water miscible oils.

Water miscible oils are still oil paints, however the suspension oil goes through a process which makes it soluble in water, removing the need for the hazardous solvents. The finished painting still has the same advantages as traditional oils, but also the same limitations regarding drying times.

Oil paintings are usually painted on stretched canvas, canvas boards or even wooden boards.

B.) Acrylics -

These are very versatile painting mediums that have been in use since the 1950’s. In effect the pigments are held in an acrylic polymer emulsion (liquid plastic) which is water soluble initially, but water proof when it 'sets'.

By adding different amounts of water to the paint before it is applied, acrylic painters can use both watercolour or oil ‘techniques’ to produce different styles of painting. That is not to say that an acrylic painting using oil techniques will look like an oil painting or that an acrylic painting using watercolour techniques will look like a watercolour. They have their own distinct quality.

Acrylics dry much quicker than oils, meaning they are harder to work once they are applied, making them more difficult to blend. When compared to watercolours acrylics have the advantage that they are much more lightfast, but they do not have that transparent quality that watercolours possess.

Perhaps the biggest advantages for painters in using acrylics over oils are the fact that it dries quicker, meaning layers can be built up quickly and a final varnish applied within a week of the painting being completed.

Some painters use acrylics in order that they do not need to use harmful solvents and the brushes can be cleaned using only water.

Acrylic paintings are usually painted on stretched canvas, canvas boards or even wooden boards. In addition, acrylics can be produced on a wide range of rigid materials including metals.

C.) Watercolours -

In watercolour paints the pigments are held in a suspension of water and gum arabic.

Watercolours are available In tablet form (referred to as pans) and in tube form. Both pans and tubes contain concentrated pigments which are dissolved into a usable form by adding water.

A watercolour painting is built up using thin layers of paint which rely on the whiteness of the paper underneath to provide the light tones.

There are a couple of issues with watercolour portraits, they can fade if left exposed to strong sunlight and they are more susceptible to damp than acrylics or oils.

Watercolour paintings are usually painted on specialist paper which is available in a range of thicknesses and surface finishes (smooth to heavily textured).

Thinner (lighter weight papers) can have a tendency to buckle if they are over wetted. Watercolour paintings are normally protected by a layer of glass.