The underpainting is, as its name tells, the layer underneath the upper surface of your final work. Although it is only meant to be a stage in the process, underpainting gives you a solid foundation for your pastel and set the mood of the overall painting. Part of the underpainting will show through the pastel strokes and change their appearance by simultaneous contrast.
When using an underpainting, you need to consider the archival consequences (would the work be damaged over time?) and if the substrate you use is suitable for a particular technique.
Underpainting with pastel: a common way to create an underpainting with pastel is to lay colours using broad strokes with the side of your pastels sticks and then to blend the marks in order to obtain a soft background to build upon. You can brush the pigments with a stiff brush loaded with water or rubbing alcohol. Different brand of pastel will react in different ways to water and alcohol, so it is a good idea to test beforehand. After establishing the underpainting with pastels, I like to apply a light spray of fixative. This way, the underpainting is not disturbed by later work on the surface and you don’t end-up with muddy colours, in particular if you are using complimentary colours in your underpainting. If you apply any liquid for blending, you need to use a heavy paper (or a board) so that the surface does not buckle.
I laid the colours for the underpainting of Cardiff Gallery, using broad strokes and the side of pastel sticks
The pastel pigments are blended together after a wash of rubbing alcohol applied with a soft brush.
Underpainting with watercolour: This is a good technique if you use watercolour paper as your support. As already mentioned, use a paper sturdy enough so that it does not buckle, some pre-mounted paper or a pastel board. Paint freely with a large brush, wet on wet. Let the paint flows: you are preparing the ground for your pastel, not painting a watercolour.
Watercolour underpainting for Bluebell wood - As the paper was prepared with Colorfix pastel gesso, the surface was waterproof and the watercolour did not react as usual.
Underpainting with gouache or acrylic: Gouache or acrylic work well for underpainting. The difference with watercolour is that you can obtain opaque layers of paint. You must be careful to paint thinly, otherwise the paint will fill the texture of the pastel paper and the paper will not hold pastel pigments.
Underpainting with oil paint: The first precaution to take is to make sure that the support you use can take oil. If you are using paper, this means applying some gesso to protect the paper from the chemicals in the paint. Use oil paint thinned with turpentine or mineral spirit and let the colours drip and mix together. You must paint thinly to retain the tooth of the surface. The advantage of this method is that the oil paint used in thin washes will dry quickly. As mineral spirit can soften adhesive, it is better to use this technique on unmounted primed paper.
Oil underpainting for Summer Walk
Make sure your underpainting is fully dry before you continue with the next stage of your pastel painting.
The choice of colours and tones for your underpainting depends on the effect you want to achieve. Here are four options to explore:
1. Create a monochromatic underpainting. For a snow landscape, you could select a pastel paper tinted with a mid-range neutral colour (grey for instance) and use a dark colour as underpainting to block in trees and rocks. This will make it easier to get the correct tones and colours for the snow and highlights.
2. Another option is to use a contrasting colour temperature in your underpainting. Staying with our snow landscape, you could use red, orange and yellow in your underpainting in order to make the blue strokes sing.
3. Use colours which are similar to the ones in the final painting. To make this work, you need to create some type of contrast with the final layer, either by using contrasted tones in your underpainting or by keeping it loose and soft.
4. Paint colours randomly across the whole surface. Provided you keep the number of colours low to preserve some unity, this technique may produce interesting effects if the underpainting shows through the final layer.
As always, you need to try and experiment in order to find the techniques that fit your style. However, don’t get stuck with a single technique because they all serve different purposes.
Getting started with pastel
Framing pastel drawings and paintings
Product test - Colourfix pastel primer
Pastel Underpainting Painting technique