Painting Foundations: Sizes, Grounds and Acrylic Primer

Lay a solid groundwork for your painting with a good foundation, an important step to help your chosen medium and substrate adhere to one another and ensure the longevity of your work. Selecting the right kind and combination of foundation layers begins with the kind of support you wish to paint on and your chosen painting media.

Sizes. Fabric supports, such as cotton canvas and linen, benefit from an initial layer of size, especially when using oil paint. Size permeates the fibre and seals it, protecting the fabric from the degradation that occurs when oil paint comes in direct contact with these natural fibres. Wood substrates should be sized with a wood sealer to prevent warping when water-based media is used. Traditional size, made of animal hide or rabbit skin, expands and contracts with atmospheric humidity which may cause cracking in the painting over time. Many contemporary oil artists counter this by choosing a ready-made PVA (polyvinyl acetate) size as it does not absorb humidity and is dimensionally stable.

Grounds. After sizing your surface, you may then apply ground to provide a white foundation and also bond the paint to the canvas. Traditional oil grounds are made with chalk or gypsum, white pigment, and linseed oil and produce the best bond between a foundation and oil paint. Specialty acrylic grounds are also available. Use white absorbent ground to prepare surfaces for watercolour effects, or select a pastel ground for work in pastel and similar media.

Gesso. Meaning gypsum or chalk in Italian, traditional gesso is a mixture of calcium carbonate (chalk/gypsum), titanium dioxide, animal hide or rabbit skin glue, and water. While too brittle for a fabric support, it works wonderfully to prime rigid surfaces such as wood and its matte texture provides a perfect base for tempura work.

Today, gesso usually refers to acrylic primer. Acrylic gesso creates a strong flexible base for both oils and acrylics. When used in acrylic painting, it may act as both size and ground. While a good primer for many surfaces, it should not be used over an oil size or a surface that has a previous layer containing oil as the oil will prevent proper bonding between the surface and the acrylic primer.

Before beginning your next painting, consider the foundation on which it will sit. Time spent on research and preparing the right base may make the difference between your painting lasting decades or centuries.

For detailed information on how to select and use sizes, grounds, and gesso, see our How-To Handouts Painting Grounds and Painting Grounds at Opus, available online at www.opusartsupplies.com/how/handouts and at all Opus stores.