Acrylic paints are notorious for drying rapidly, but with the right approach this can be one of their strengths.
Oil paints are a joy to use and give excellent results but take a long time to dry; it can be years before you can apply the final coat of varnish. Watercolours are immediate and sparkling, but careful planning is needed if the painting is not to become over-worked and 'muddy'.
Pastel drawing is one of the most subtle and seductive media in experienced hands, but the results are a nightmare to preserve as the final image is so fragile and powdery. The list goes on. Artists have grown accustomed to the problems presented by these other media over centuries of use, but acrylic paints are still something of a novelty to us having only been available in Britain for just over 70 years.
All paints are basically made of a combination of pigment and a binder, which is usually called the medium. In acrylic paint, the medium is an acrylic polymer suspended in water. This has the great advantage that it can be diluted with water to make thin washes. It also means that paint straight out of the tube has a certain amount of water in it. The colours of anything wet, the clothes in the washing machine, for instance, always look brighter and more intense than when they are dry. Because of the presence of water in the tube of paint in the first place, a strictly 'dry-brush' method is impossible with acrylic paint. If a drier oil paint is required, it can be left on a piece of blotting paper and the medium, the oil, will leach out. If this attempted with acrylic paint, it would just colour the blotting paper.
The acrylic paint film normally dries with a matt finish. So, the pigments in the paint will seem brighter when just applied and appear to 'sink back' or 'fade' when they dry out. There are several things that can be done about this. When the picture is completely dry a gloss varnish can be applied. Many manufacturers now produce varnishes specifically for acrylic paintings and a varnish will deepen the tones and 'bring back' the colours. Many artists mix matt and gloss varnishes together until they find a formula that dries to the degree of gloss that most suits their work. This is all a matter of experiment and practice.
Alternatively, an acrylic gloss medium can be added to the wet paint while it is being worked on the palette. Depending on how much is used, the matt finish of the paint can be varied. It should be remembered that the more medium added to the paint, the less the proportion of pigment that is present. If too much medium is added, the paint will become transparent.
The speed with which acrylics dry should be regarded as an advantage. Thin washes dry as fast as watercolour and a painting can be finished in one day even using the paint quite quickly. Unfortunately, this also means that quite often the paint dries on the palette before it has all been used. I always mix my paints on a piece of glass or a white china plate and while this means it is easy to clean afterwards, it also means that I am constantly scraping away dried up paint.
Stay-Wet palettes are available specifically for acrylic paints. The plastic palette has a small reservoir of water that keeps the paint damp and workable for some time.
There is a tradition in oil painting of 'fat over lean', which means that the first layer of the work should be executed with thinned down paint and the subsequent layers gradually built up using increasingly thicker paint. This is also true of acrylic paint. Keith Holmes began his painting by blocking in the main areas of colour very roughly using thin washes. The design was built up in layers adding less water as the work proceeded, until the highlights were added impasto.
After this stage Keith was able to make subtle alterations to the balance of the composition with transparent glazes using paint and acrylic gel medium. When it was completely dry, he gave it a coat of acrylic varnish which brought out all the more subdued tonal changes in the dark areas.
Acrylic paints have their problems, but this is often the result of a painter trying to use them in the same way as another type of paint. Acrylic paint has its own rules. If these are observed, it will be found that the bad points are far outweighed by the good.'
Original article by Sheila Fairbrass - The Artists & Illustrators Magazine