Varnishing an Acrylic Painting

By Jim Hingst

A finished acrylic painting often has some areas with a matte finish and other areas with a gloss finish. This look is usually off-putting.  Varnishing your painting provides the surface with a uniform finish.

Commercially available varnishes come in gloss, satin and matte finishes. Varnishes usually with alter the appearance of your painting. A gloss finish will typically increase color saturation. On the other hand, matte finishes will soften your colors.

Varnish also provides your painting with a protective coating. Acrylic paint, which is comprised of very large molecules, has pores or spaces between these molecules.  These pores allow the paint to breathe. They also allow one coating to better adhere to a subsequent coating layer, ensuring good intercoat adhesion. 

The soft, porous surface of an acrylic painting also allows other substances to bond to it, including dirt, fly specs, pet hair, smoke and oils. To prevent these contaminants from soiling our painting, you need to protect it. That’s what the varnish coat does. It protects the surface of your painting from dirt and those other contaminants. It also protects the pigments of the paint from UV degradation.

The Isolation Coat

As the name suggests, an isolation coat creates a permanent barrier that separates your painting from the varnish. The purpose of this coating is that it allows easier removal of varnish when needed.

While a pre-mixed isolation coat is commercially available, you can mix your own using Golden’s Open Acrylic Gel Gloss and water. (There are many different products on the market. My choice is the Golden line of paints, mediums and varnish.)

The isolation coat provides a glossy surface. Before applying this coating, sign your work. Photographing your artwork before varnishing is also easier because you do not have to contend with reflections.

Pictured above is my version of Sandro Botticelli’s Portrait of a Young Man, painted on aluminum composite material with Golden brand acrylic paints. In varnishing an acrylic painting, an isolation coat is not absolutely necessary but it is recommended because it allows for removal of varnish in the case that the work needs restoration.

Procedure. Before coating the painting with an isolation coat, make sure that the paint is thoroughly dry and cure. A recommended practice is to wait a month before applying the isolation coat and varnishing.

Mix the Open Acrylic Soft Gel Gloss with distilled water at a ratio of 2 parts gel with 1 part water in a clean jar. Do not alter this ratio by adding extra water. When you are mixing an isolation coat, stir very carefully so you do not induce air into the mixture. Bubbles in the coating can result in pinholes in the finish.

In coating your artwork with an isolation coat and varnish, first lay the painting on a flat horizontal work surface. Make sure that you work in a well-lit workspace. You may wish to light the surface that you are coating with a clamp-on light directed at the painting at a 45⁰ angle. With good lighting, you should see any areas that you miss as you apply the isolation coat.

Using a synthetic flat brush at least 2” wide, apply a uniform coating of the mixture. Some painters recommend buying may one brush which you dedicate for varnishing.

Use overlapping strokes to ensure complete coating of the surface. After coating the painting, tip off the excess with a clean dry brush to eliminate brush marks. In applying an isolation coat, you should work quickly before the coating gets tacky.

In most cases, coating the surface with a brush works best.  You can also spray this finish. Just remember, that anytime that you atomize a fluid, a good portion of it is in the air, even if you cannot see it. Some of the atomized fluid will get on surfaces where it is unwanted. You can also breathe some of it. If you decide to spray, make sure that it is in a well-ventilated area and that you wear an air respirator. Whether you brush or spray the isolation coat, cover the artwork so dust does not settle on it while it is drying.

Spraying the varnish is sometimes a better choice if your painting is highly textured. On these surfaces, spraying deposits a uniform coating, minimizing the potential for the coating to pool in the valleys on the painting surface.

Test, Don’t Guess.

Before varnishing a prized painting and being shocked by unexpected results, a good practice is to test the isolation coat and varnish on a test panel.  Prepare your test panel the same way that you prime and paint the substrates that you use.

In painting an isolation coat, it is usually better to apply two thin coats rather than painting one thick one. In applying two thin isolation coats, you should generally wait a minimum of six to eight hours between coatings.

Types of Varnish

Acrylic paints generally dry to a dull, matte finish. Coating your painting with a varnish coat not only protects it, but also can make the colors shiny and vibrant as when you first painted them.

Ideally, the varnish that you select will be removable. Keep in mind that not all are. The removability characteristic allows either you or someone else to strip the varnish at a later date without damage to the painting. Varnish is generally dry to the touch within 24 hours of application. However, it can take the varnish several weeks before fully curing.

Two types of varnish are available: polymer varnish (which is water-based) and solvent based. Polymer varnishes are thinned with water. Mineral spirits, on the other hand, are used to thin solvent-based finishes.

Water-based Varnish

Golden’s waterborne acrylic polymer varnish with UVLS (Ultra Violet Light Stabilizers) applies easily and cleans up with water. Polymer varnish is formulated for application on acrylic paintings. Golden’s polymer varnish is available in gloss, satin and matte finishes. It is removeable using ammonia.

While some painters prefer a matte appearance, coating with a matte varnish can lighten dark colors and sometimes can result in a milky appearance. This is exactly the reason that you should test components before using to prevent unexpected surprises.

Solvent-based Varnish

Some artists prefer solvent-based varnishes, such as Golden’s MSA (Mineral Spirit Acrylic) Varnish with UVLS (Ultra Violet Light Stabilizers). This mineral spirit-based acrylic resin coating is compatible for use in protecting acrylic, oil and alkyd paintings. This varnish is tougher than waterborne acrylic polymer varnish, yet it creates a flexible and removeable protective coating for use in both interior and exterior applications. Because the solvent based varnish is less porous than the polymer variety, it is less likely to trap dirt and dust.

Compared to waterborne varnishes, Golden’s MSA varnish is easier to apply and self-levels to a smoother finish. It also has a longer open time, so you don’t need to work so quickly as you do when coating with a polymer varnish.

While MSA varnishes provide slightly better clarity and finished appearance, they require thinning with mineral spirits, which might concern some amateur painters working in their homes. If you select a solvent-based varnish, use it in a well-ventilated room. Golden’s MSA varnish is available in gloss, satin and matte finishes. It is removeable using mineral spirits.

A Final Note. Always read the manufacturer’s literature before varnishing your artwork. In putting on your varnish, it is recommended that you apply very thin coats. Some people apply as many as four to six coats to achieve a desired look. Do not be alarmed if the varnish does not look the way you expect while it is wet. Matte finishes will usually look glossy until they dry. Some finishes appear cloudy but clear up after drying.

If you use different types of varnish or vary your application procedures, write a description on the back of your painting explaining what you did.  This tells someone who is restoring your painting in the future, what they need to do to remove the varnish.

Do You Have Questions or Comments?

About Jim Hingst: Sign business authority on vehicle wraps, vinyl graphics, screen printing, marketing, sales, gold leaf, woodcarving and painting. 

After fourteen years as Business Development Manager at RTape, Jim Hingst retired. He was involved in many facets of the company’s business, including marketing, sales, product development and technical service.

Hingst began his career 42 years ago in the graphic arts field creating and producing advertising and promotional materials for a large test equipment manufacturer.  Working for offset printers, large format screen printers, vinyl film manufacturers, and application tape companies, his experience included estimating, production planning, purchasing and production art, as well as sales and marketing. In his capacity as a salesman, Hingst was recognized with numerous sales achievement awards.

Drawing on his experience in production and as graphics installation subcontractor, Hingst provided the industry with practical advice, publishing more than 190 articles for  publications, such as  Signs Canada, SignCraft,  Signs of the Times, Screen Printing, Sign and Digital Graphics and  Sign Builder Illustrated. He also posted more than 500 stories on his blog (hingstssignpost.blogspot.com). In 2007 Hingst’s book, Vinyl Sign Techniques, was published.  Vinyl Sign Techniques is available at sign supply distributors and at Amazon. 

Slides of Jim's Artwork

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