Gessoing Canvas for Oil Painting

This picture is in the public domain.

Artists have primed the substrates for their paintings with gesso for more than 500 years. Gesso is an Italian word.  It means gypsum or chalk.  The traditional recipes, as reported by Cennini, the artist and chronicler of Renaissance crafts, utilized powdered gesso mixed with heated rabbit skin glue. I was amused that in The Craftsman’s Handbook Cennini describes making gesso to mixing pancake batter. These time-tested techniques are still practiced today by purists in both the kitchen and the fine arts field.

For the iconoclasts among us, there are simpler alternatives. Today you can buy Aunt Jemima pancake mix in a box and you can also purchase pre-mixed acrylic gesso in a squeeze bottle or jar.

However you decide to prime your canvas, the purpose is the same: to protect the fabric from the oil paint. Without the priming, the oil will soak into the canvas, which will deteriorate the fabric. Priming also makes the substrate more rigid.

Even if you buy your canvas primed, you may want to apply additional coatings. That way, you can control the texture of the canvas. If you want a smooth surface to paint on, you may want to apply two to five additional coatings. Smoother surfaces are often desired for portraits or if you are painting fine details.

The traditional method of prepping a canvas is a two-step process. First, the surface is sized with rabbit skin glue. The size performs two functions. It seals the surface of the canvas, protecting it from the acidic oils in the paint. Its second function is to anchor or bind the ground to the canvas. As an alternative to rabbit skin glue, you can also use a PVA (Poly Vinyl Acetate) size. The second step in the traditional method of preparing a canvas is to coat the canvas with the ground or gesso.

The alternative method is a one-step process, in which the canvas is coated with an acrylic gesso. Today, prepping the surface of canvas with acrylic gesso is the preferred method. It serves a dual function. It acts as a size, sealing the surface of the canvas. It also serves as the ground for the painting.

The Traditional Method.

The traditional way to prime a canvas is very similar to priming a picture frame, when you are doing traditional water gilding.  The first step is to coat the canvas with rabbit skin glue. As you may have guessed, rabbit skin glue is made from rabbit skins.

The animal hide glue acts as a barrier coat, sealing the surface of the canvas and protecting it from any acids in the paint, which will cause it to rot.  After the hide glue is applied and has completely dried, several coats of gesso are brushed on to build up the surface.

The traditional method of prepping a canvas utilizes rabbit skin glue. Some feel that the hide glue tightens up the canvas. Others believe that because the hide glue is hygroscopic, which means that it can readily absorb and release moisture from the air, and thereby allowing expansion and contraction, it can result in cracking and delamination of the paint. Because hide glue is hygroscopic, finish paintings should be kept in an environment with a relative humidity between 30% and 60%.

Preparing the Rabbit Skin Glue. In its dry state rabbit skin glue is dehydrated glue.  To rehydrate the glue you must add water. 

Rabbit Skin Glue is available in granular form.

Recipe for Rabbit Skin Glue. Below is a basic recipe:

In a clean glass canning jar with a lid add 40 grams of rabbit skin granules or pellets by weight.

Add 1 quart of distilled water to the glue, and cover the jar to prevent any contamination.

Wait at least 2 to 3 hours for the rabbit skin glue to absorb the water.  Better yet, mix the rabbit skin glue and water the day before you intend to use it and allow it to soak overnight.

Before heating the glue, strain the mixture using a kitchen strainer.

In a double boiler, heat the glue/water mixture to a temperature between 98.6°F and 110° F.  Carefully monitor the temperature using a candy thermometer. You can also monitor the temperature of the water with your hand. The water should feel warm.  If the water is too hot to put your hand in it, it is too hot for the glue.  Excessively high temperatures above 120˚F  will destroy the adhesive properties of the glue.  Continue to heat the glue until all of the granules have dissolved and disappear. If you overheat the glue, you have ruined it. Just throw it away and start over.

Sealing or Sizing the Substrate.  Brush on a thin coat of rabbit skin glue onto the canvas. If the texture of the canvas is rough you should brush on a second thin layer of the glue, applied about twenty minutes after the first coating.

Gesso.

The main ingredient used in preparing the gesso layer is calcium carbonate (CaCO3 ), which is found naturally in limestone, chalk and ground up sea shells.  If you have ever used whiting, that is calcium carbonate.    The calcium carbonate is mixed with a binder, such as rabbit skin glue. When you are buying whiting, caveat emptor (buyer beware).  Not all whiting is the same.  The grit of the product will vary from one part of the world to another.

In addition to the calcium carbonate and rabbit hide glue, other components are added to the mixture.  The addition of linseed oil, for example, can improve the flow out of the gesso, yielding a smoother surface.

During the very best of conditions, it can take days for the gesso to completely dry.   High relative humidity can prolong the process extending the drying period to weeks.

Gesso combines a filler, which is the calcium carbonate, with a binder, which is the rabbit skin glue.  The strength of the gesso is directly related to the ratio of the filler to the binder.  That ratio is very important to how the gesso performs.  If too much filler comprises the mixture, the binder cannot hold the mixture together and the gesso can crumble when pressure is applied to it.  If the mixture has too much binder, the gesso becomes too hard. When this happens the gesso can shrink and crack and can break away from the substrate.

The ratio of rabbit skin glue to whiting is critical in determining the hardness of the gesso.  The more glue that you add to the mixture, the harder the gesso will become. As you add more whiting, the gesso becomes softer. If the gesso is too soft, it can crumble under pressure.  The harder the gesso is, the more brilliant the burnish can be.  So why not mix the strongest gesso you can?  One problem is that the harder the gesso is, the more difficult and time consuming it is to sand. Even worse, if the gesso is too hard, it can become brittle and potentially can crack.

The amount of water in the gesso mixture does not affect its hardness.  It does, however, determine the viscosity of the gesso.  Thin mixtures are easier to brush, and yield a smoother finish surface with less brush marks. The disadvantage is that you will need to apply more layers of these thin coatings to achieve the desired thickness.

Thick mixtures require fewer layers of gesso.  If the gesso is too thick, you will produce brush marks. If you see brush marks as you are coating the gesso, you should thin the mixture with distilled water.

As mentioned earlier, coatings are applied wet on wet. Subsequent layers are applied to previous ones before the gesso dries. If the gesso dries before you coating the next layer, you can rewet or dampen the surface with a wet sponge.

Because the ratios of the various components are very important, follow any of the recipes to the letter when you are starting out.  You can always vary the recipes, after you have experience under your belt.  When you are mixing the components of the recipes all dry ingredients are measured by weight; all liquid ingredients are measured by volume.  That means that you will need an accurate digital scale and graduated glass measuring cups.

Recipe for Gesso

Remove the glue mixture in the above recipe from the double boiler. To this mixture gradually add 1.5 cups of whiting.  To prevent lumps, use a flour sifter to add the whiting.  By sifting the whiting you will prevent lumps.  Using a wooden spoon slowly stir the mixture until the ingredients are completely combined, taking care not to form bubbles.  Bubbles in the mixture can result in pinholes in the gesso. Vigorous stirring as you are heating the mixture will generate bubbles in the gesso. Bubbles in the mixture quite often result in pinholes after the gesso dries on the substrate.  To prevent the creation of bubbles, gently stir the mixture.

On top of the glue/whiting mixture, add 1 tablespoon of denatured alcohol and ½ teaspoon of boiled linseed oil. Allow the glue/whiting mixture to rest for one hour.  The alcohol and linseed oil will help dissipate any bubbles which have formed.

After the resting period, strain the mixture twice through a paint strainer.

If you want to make sure that the gesso is neither too hard nor too soft, follow the recipe exactly. Will any one recipe be perfect for every working environment? Probably not.  Differences in humidity and shop temperature may require that you modify the recipe to satisfy your unique requirements.

Apply the gesso while it is still warm, this will ensure good flow out.  Some artists recommend the addition of boiled linseed oil the gesso to improve the flow of the gesso and ensure a smooth coating. Others recommend against it, believing that the oil contaminates the mixture, potentially compromising the adhesion of the gesso to the substrate.

Typically six to eight coatings of gesso are applied.  After you apply the initial coating of gesso, you should apply each subsequent coating before the previous coating is completely dry.  This practice ensures good intercoat adhesion between layers of coating.

If you are preparing a canvas using the traditional method, you should wait 6 months before painting.

The Alternate Method Utilizing Acrylic Gesso.

Priming a canvas with rabbit skin glue is the old school method. The newer alternative is to prime the surface with a ready-to-use acrylic gesso. Using the gesso in a bottle is faster and easier that mixing your own.  And just because the gesso is ready-made, does not mean that it is any less durable or effective in protecting the canvas from the degrading effects of oil paint. On the contrary, many will argue that the newer acrylic gesso primers are less likely to crack, because they are not hygroscopic.

When you are shopping for a ready-made gesso mixture, be sure that you read the label before you buy the product, making sure that the product is suitable for either acrylic or oil paints. As a word of caution, before you use any of these products, read the instructions before use.

When buying gesso primer, be aware that there are a couple of different options. Acrylic primers are available in white or clear. You can tint the clear variety  with artists acrylic paint to tint the canvas. These acrylic primers are water-based. Oil based primers are also available. The oil based variety is the type that you would use with rabbit skin glue.

Advantages of Acrylic Gesso:

• Ease of use. You can literally pour the acrylic directly on your canvas and spread it over the surface with a brush.
• Versatile. You can use it on a variety of surfaces other than canvas, including hardboard (Masonite), wood and paper.
• Compatibility. Works with acrylic and oil based paints.
• Fast drying. Acrylic gessoes dry much faster than oil based types.
• Flexible. Over time canvases prepped with rabbit skin glue can crack. Acrylic gessoes provide a flexible ground.
• Tintable. By mixing in a little acrylic paint, you can tint the gesso. NOTE: Do not mix with oil paints.
• Easy clean up. As soon as you are finished coating the canvas, clean your brush with soap and warm water. CAUTION: Do not allow the acrylic gesso to dry in your brush. Once it dries, it is insoluble.   

For paintings with a good deal of detail, many artists prefer a smooth finish on the surface of the canvas.  To achieve a smoother surface finish, apply at least three thin coats of gesso. By adding a little water, you can thin your gesso mixture. Do not overthin the mixture, however. Many artists believe that you should apply as many as four or five thin coats of gesso to protect the fabric and prevent strike through on the canvas.

Before applying the acrylic gesso, wipe the canvas down with a damp sponge. (Photo 1.)

Photo 1.

Apply a thin coating of the gesso to the surface of the canvas, brushing in one direction. (Photo 2.)  Brush on the subsequent coating of gesso in a perpendicular direction.

Photo 2.

As well as coating the primary surface of the canvas, also be sure to coat the edges and sides of the canvas. (Photo 3.) Failure to prime the entire canvas can result in the deterioration of the fabric. 

Photo 3.

Allow the coating to thoroughly dry, before brushing on a second coat.  Drying times will vary depending on the ambient temperature and humidity in your shop or studio.  Generally, a thin coating of gesso will dry in one to two hours.

After applying the gesso, wash your brush thoroughly in warm water, making sure that all of the residual gesso has been cleaned from the hairs of the brush.

Between applications of gesso, lightly sand the surface with either 150-grit  or 220-grit sandpaper. (Photo 4).) Sanding the surface achieves two ends.  First, it smoothes the surface, eliminating any brush marks, ridges or rough spots. Secondly, it gives the dried coating of gesso some tooth, so that the subsequent coating of gesso adheres to the precedent coating. After sanding the gesso, wipe any dust from the surface with a clean rag, before applying another coating.

Photo 4.

Each layer of primer should be applied using brush strokes perpendicular to the strokes used to apply the precedent coating of gesso.

After you have gessoed the canvas, wait 24 to 48 hours before painting.

Which is Better: Natural or Synthetic Brush?

A synthetic brush (on the right) is preferred for applying acrylic gesso.

When gessoing a canvas, using the right brush for the job, will result in a smoother surface. I have tried both natural and synthetic hair brushes. I my opinion a synthetic brush produces a more even finish with fewer streaks, when coating a canvas with acrylic gesso.

Here’s another piece of advice. Invest in a good brush that will last for years. Designate that brush for gessoing. And then take care of that brush.

The problem with a natural bristle brush is that the hairs absorb water and become coarser and clump together. That results in streaks in the gesso. Now unless you like sanding, buy a good quality nylon or polyester brush.

Now that I have convinced you to use a synthetic brush, here’s how to care for it. Before you use the brush, soak it in water. After you remove it from the water, squeeze out the excess water between layers of either paper toweling or a clean rag. Soaking your brush will prevent the acrylic gesso from caking in the ferrule as well as facilitate the cleaning.

To clean your brush, first squeeze out the excess gesso from the hairs of the brush between paper toweling. Then rinse out the gesso under warm water. Next, wash the bristles with soap and water. For this step you can use a bar of Ivory soap or another brand with no moisturizers or you can use Joy dishwashing liquid. When the bristles of the brush are thoroughly clean, lay the brush flat and allow it to dry.

Always clean your brushes immediately after using them.  You should also wash out your brush, if the gesso starts to gunk up in hairs. Remember, acrylic gesso dries fast – really fast.

If you allow the acrylic gesso to dry, the brush is trashed. Once the gesso dries, it is insoluble in water. Here’s another “Bozo No No”. Never leave your brush standing in a container of water. This practice will result in distorting the hairs of the brush.

About Jim Hingst: 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 150 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 325 stories on his blog (hingstssignpost.blogspot.com). In 2007 Hingst’s book, Vinyl Sign Techniques, was published.

Slides of Jim's Artwork

© 2015 Jim Hingst