Answers by Douglas Purdon, SCA — For more information contact Doug @

Q. Are there any rules to be followed when painting with acrylics?

A. Acrylic is the 'imagination material' and more artists are working with acrylic paints than ever before. Some of the reasons for this are their ease of application, lack of toxicity, speed of drying and the ability to break rules that must be observed when working with other materials.

Unfortunately, however, many artists are under the impression that there aren't any rules at all to be followed when working with acrylic paints. While acrylics do allow a level of creative freedom that hitherto was unavailable to painters there are still rules that must be followed to produce a painting that will not deteriorate over time. These rules apply to all acrylics independent of the manufacturer.

Q. How much should I thin acrylic paint with water?

A. Acrylic paints are a mixture of water, plastic resin and pigment. When the water evaporates the long-chained plastic molecules link, trapping the pigment producing a very permanent and flexible paint film.

Acrylics should never be over thinned with water. As the water evaporates and doesn't become part of the paint film, over thinning with water produces an unstable and weak paint film. If you wish to dilute the paint it is recommended that you add acrylic medium along with the water so that you will maintain the stability of the paint film.

Q. Do acrylic paintings have to be varnished?

A. Once dry, acrylic paintings should be varnished to protect them from dirt and pollutants in the air. Remember that an acrylic medium is NOT a varnish. It is the same material that the paint is made from and therefore not removable. A varnish, to fulfill it's purpose, must be able to be removed without damaging the painting.

While acrylics are touch dry within hours they shouldn't be varnished until totally dry to avoid water being trapped under the varnish. A general rule is to allow a week for thin films and at least a month for heavy applications.

Q. Can I use acrylic paint on outside walls?

A. Acrylic paint is hydroscopic. It will absorb moisture out of the air or from a damp surface. If painting is to be done on an outside wall or location where moisture can penetrate from behind such as an outside wall, or a high humidify environment like a swimming pool or bathroom it should probably not be varnished as the moisture could be trapped behind the paint surface and cause blistering, separation or promote the growth of mould.

Q. Do acrylic paintings become brittle over time?

A. All Acrylic paint films have a 'glass transition temperature' this is a temperature where the paint film will start to lose it's flexibility and become brittle. This can vary depending on the manufacturer and the binders that are used but usually occurs at temperatures under 44 degrees Fahrenheit. At lower temperatures the paint film will become increasingly brittle and can suffer cracking and peeling. Acrylics should never be painted over oil paint or oil paint over acrylic. Both materials have completely different properties and the resulting painting will develop major problems over the passage of time.

Pay attention to your support as it is the foundation of your painting. While acrylics remain flexible and will withstand normal movements of the support that doesn't mean that they can be tightly rolled or harshly treated.

Acrylic paint is the MOST stable and permanent material available to the artist today and if properly used will outlast all other materials. While the binders used in some of earlier acrylics have deteriorated the ones used today are stable and according to some conservators will last for hundreds of years provided they have been properly used.

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