A guide to sizing and priming canvas

What is sizing?

Sizing is the first step in preparing a canvas. It seals the surface, forming a protective barrier between the support and the paint layers. This reduces absorbency, preventing paint (especially oil colour) from soaking into the canvas and weakening the fibres over time.

Key points:

• Protects the canvas from rotting and yellowing
• Prevents paint from being absorbed, keeping colours vibrant
• For oil painting, size the canvas with rabbit skin glue before applying primer

What is priming?

Priming, often using gesso, creates an even, smooth surface for painting. It ensures paint adheres properly and brush strokes flow easily. A well-primed canvas also tightens as it dries, giving a taut, durable surface.

Benefits of priming:

• Ensures even absorption and adhesion of paint
• Enhances colour vibrancy
• Provides a smooth surface for brushwork

Sizing, priming, and underpainting: what’s the difference?

• Sizing: Seals the canvas to protect fibres and prevent paint absorption.
• Priming: Creates an even ground for painting while also reducing absorption and supporting the canvas.
• Underpainting: The first layer of paint applied after priming. Usually tonal and lean, it helps plan composition and tone. Common methods include:
• Imprimatura: Earth tones like umber and sienna
• Grisaille: Shades of grey
• Verdaccio: Grey-green and olive tones

How to prime your canvas

Primer, often referred to as gesso, is applied to a dried sized canvas to create an even surface before painting. Applying several layers will result in a smoother finish, and many artists choose to lightly sand the dry gesso between coats for added refinement, allowing at least an hour between each layer. Before beginning your painting, ensure the final coat of gesso has fully dried, waiting a minimum of 24 hours. For acrylic paintings, one or two coats of acrylic gesso are usually sufficient, while oil colour typically requires two to four coats. Alternatives to gesso include oil painting primer, thixotropic, or oil-modified alkyd resin mediums. Winsor & Newton’s ready-to-use oil painting primer requires no thinning or stirring and can be applied to porous surfaces such as glue-sized canvas, wood, or paper without sinking in. A small amount of oil colour can also be mixed into the primer to create a tinted ground. Oil primer produces a smoother surface, whereas thixotropic and acrylic primers offer more texture or tooth for the paint to adhere to.

 

Priming different types of canvas

• Cotton: Acrylic gesso is generally preferred, although oil primer is also an option.
• Linen: Acrylic gesso or oil primer can be used. Heavier linen can be difficult to stretch properly because it’s harder to fold neat corners around the stretcher, but if you can master this process you’ll benefit from the smoothest and stiffest painting surface.

Pre-primed canvas options

You don’t have to size and prime a canvas yourself. Winsor & Newton offers pre-primed canvas options:

• Acrylic-primed cotton and linen pre-stretched canvases in various sizes and depths
• Rolled, ready-primed cotton canvases if you want to avoid priming but prefer to stretch your own canvas, though you’ll need canvas pliers
• Canvas boards: Stretched and primed cotton canvas on a stiff backing, ideal for studies or if you’re just getting started with oils.

Making pre-primed canvas even smoother

Even pre-primed cotton canvases can benefit from additional layers of gesso to make them smoother. There is also Winsor & Newton Cotton Smooth canvas which is specially designed for fine detail work with its ultra-fine weave and ultra-smooth