While many of the tools and methods used to create a painting have evolved over the centuries, some things never change—because they can’t. For example, acrylic paint dries by evaporation, while oil paint dries by oxidation. Oil paint is, in its simplest form, a mixture of three things—binder, pigment, and thinner. You see, things like don’t change, but methods and tools? Well, most methods and tools have to change with the times. And most of the time, it’s for the greater good. Such is the case with sizing and grounds.
History of Oil Sizing & Grounds
By the 15th century, wood panels were being sealed with linen soaked in an oil-based ground. When linen canvas became the preferred surface over wood panels, a similar procedure was used to seal and prepare the canvas for painting. Unlike linen that had not been painted with oil paint, artists discovered that linen painted with oil paint deteriorated over a period of time. Direct contact between linseed oil and linen fiber was determined to be harmful to the canvas, because the linen became brittle and weak prematurely. These early failures were caused by linoleic acid in the linseed oil that attacked the cellulose fibers of the linen canvas.
Sizing (sealing) the linen canvas with gelatin or animal glue before it came in contact with oil paint extended the life of the canvas. Sizing was also used to stiffen linen canvas, so tempera and oil paints, which are hard and brittle, were less susceptible to cracking. These sizings were also water-soluble. However, variations in humidity and temperature caused the sizing to swell with moisture and become more flexible, which caused the tempera and oil paint on top to crack and flake off. Evidence of this can be seen in many famous paintings. In fact, hairline cracks can be found in the old master paintings of Rembrandt, Velasquez, and Caravaggio.
History of Acrylic Sizing & Grounds
The first commercially available artist grade acrylic paints were developed in 1955. While the adhesive qualities of these paints were excellent, adhesion to oily surfaces was not, and the existing brands of artist canvases were all made with oil-based grounds. To overcome the adhesion problem, acrylic sizings and primings were developed to tolerate both oil and acrylic paints. Although these acrylic based formulas are often referred to as “gessos,” they are not true gessos in the purist sense. Acrylic grounds or primers are flexible and suitable for use on both canvas and rigid substrates. True gesso, which is made from animal hide glue and a pigment such as whiting, is unsuitable for use on a flexible surface like canvas.
Priming with Acrylic Gesso vs. Oil-Based Ground
So why prime with acrylic gesso rather than oil-based ground? For starters, acrylic gesso is flexible and it resists cracking and yellowing. Oil-based grounds, on the other hand, can yellow and crack. This means acrylic gesso is more permanent than oil-based ground. In addition, acrylic gesso:
-Penetrates into and preserves the canvas. Oil-based grounds do not.
-Has greater adhesion.
-Is more versatile than oil-based ground. Acrylic and oil paints can be painted over acrylic gesso.
-Acrylics cannot be painted over oil.
-Can be applied to raw canvas and non-oily surfaces such as wood, paper, plaster and concrete.
Oil paints adhere to acrylic gesso because of the porosity of acrylic gesso and the canvas texture. It is not advisable to use oil paint over a thick, smooth acrylic paint surface, especially when the canvas texture has been completely covered over.
A high quality gesso such as Fredrix® Premium Gesso is recommended for best overall performance. Lower quality gessos may use plasticizers and fillers, which can affect flexibility and paint adhesion. Lower quality gessos may also require extra coats for proper coverage, so you’ll have to use more, buy more, spend more—well, you get the picture!
Visit the official Fredrix website to learn more about Fredrix® Premium Gesso and much (much) more.