Many people think of acrylic paint as impervious and indestructible once it’s dried. It is not. Acrylic paint is thermo-plastic. This means that if it gets too warm, it will get soft and can be damaged. Further, acrylic adheres to acrylic. If you set two paintings together with the surfaces touching, they may stick together, and wrapping materials can also stick or imprint their textures on the painting surface.
When the water dries out of wet acrylic paint, it leaves micro-pores throughout the surface. Varnish is a hard, protective, removable coat applied over the painting surface.
Types of Varnish
There are two types of varnish that can be used on an acrylic painting:
• Mineral spirit-based (MSA)—You can use this over anything, but it’s extremely important that you have good ventilation. Wear a respirator.
• Polymer varnish (water-based)—Golden brand polymer varnish with UVLS (ultraviolet filters incorporated) is much easier to handle and clean up. Polymer varnish is soluble in alkaline solvents and can be removed using ammonia. It also can only be used on acrylic paintings and comes in a variety of finishes: matte, satin, and gloss.
Why You Might Not Want to Varnish
Polymer varnish is not made to be painted over. Paint that is applied over varnish may not bond sufficiently which may cause a lack of adhesion over time. Further, any paint applied over the varnish will be lost if the varnish is removed.
1. An isolation coat is a permanent, non-removable layer that acts as a finish coat on top of the paint and under the varnish. Diluted soft gel gloss is used for this.
2. One of the tricky things about mixing and applying varnish is that it’s extremely easy to create bubbles because of the surfactant that is used to allow the polymer to mix with water. Mix the varnish carefully and slowly. If bubbles form, you can catch and remove them with your brush. Many people choose to spray on varnish. This has its own difficulties. Be sure to wear eye protection and a respirator.
3. Always brush on the isolation coat and the varnish with your painting flat on the floor or table. Keep it flat until it is completely dry. Dry times: isolation coat—24 hours; Varnish—3 to 6 hours between coats.
4. After applying each coat, check carefully for bubbles and for spots you may have missed. Look at the painting from the side where you can see the sheen from a light.
5. Because varnishing may cause the surface of your painting to be more reflective, you may want to photograph your work before you varnish.
6. Be sure your mixing containers and brushes are clean before you use them. If they have been sitting on the shelf for a while, they may be dusty. Little specks of dust, etc. are not your friends when you are varnishing. Also beware of loose brush fibers.
7. If your painting has a lot of texture, bubbles can get caught in grooves. Use your brush to remove bubbles.
8. If a varnished painting becomes soiled, the old varnish can be removed down to the isolation coat (see explanation above) and new varnish can be applied.
Jacqui Beck, of Seattle, Washington, is a full-time artist and art instructor and has worked in many capacities to further the arts, acting as a board member of arts organizations and director of Art for Kids in the Northwest. To see her work, visit www.jacquibeck.com. Be sure to see her work in the September 2007 issue of The Artist’s Magazine.