However tempting it might be to simply put brush to canvas when you’re feeling inspired, if you want your oil or acrylic paintings to look their best and stand the test of time, priming your surface is a must.
There are different stages to surface preparation, and the terminology can be confusing – with sizing, priming and underpainting all playing important roles. Find out more about the different stages, and get answers to all the big questions, with our guide to priming a canvas.
What is priming in painting, and why should I do it?
Priming your canvas protects your canvas from rotting. It also means your paint will sit better on the surface and not sink into the canvas. When it comes to oil colour, priming can help avoid dull patches in your finished work and make the colours stand out.
Priming gives you an even ground to work on. A smoother surface means your brush strokes will flow more easily, and the paint will sit on the surface. As the primer dries, it will stretch and tighten the canvas and make it taut.
Acrylic gesso is suitable for priming both oil and acrylic paint. For oils you can also use a solvent-based oil painting primer. If you choose to use this kind of oil primer, you should ‘size’ your canvas first with rabbit skin glue (more on this later).
What is gesso?
Gesso is a white paint mixture consisting of a binder mixed with chalk, gypsum, pigment, or a combination of all three. Acrylic gesso is an alternative to real gesso, possessing a similar absorbency or tooth that one expects from a gessoed surface.
If you want to keep the natural look of your canvas, you can use a clear gesso. To make a coloured surface preparation, you can use acrylic colour with clear or white gesso, giving your painting a toned ground base layer. Oils are not suitable in this context. You can see the effects created with different gessoes in this video tutorial.
How should I apply gesso?
It’s best to use a wide, flat brush with relatively short bristles to apply gesso, and brush it in firmly. Thinning the first coat with a little water makes it easier to apply and helps the gesso soak into the first layers of the canvas.
You apply acrylic gesso in the same way you would apply acrylic or oil gesso after sizing. Use a flat brush and apply the acrylic gesso neatly in one direction only, ensuring the gesso sits on the surface of the canvas and does not go through the canvas. This will prevent your paint seeping through the canvas and rotting the unprimed side later. When the first coat has dried, apply across the original direction in one direction. Allow to dry. Then for your final coat apply across the last coat in the same direction as your first. This will ensure you have an even ground across your canvas that creates a protective layer between your paint and the canvas.
For a demonstration and more information, watch our video masterclass on priming your canvas.
How many coats of gesso do I need?
As an average, about three coats. For acrylic paintings, one or two coats of gesso are normally recommended. For oil paintings, you need two to four coats. But the precise number of coats depends on the absorbency of your surface and your personal preference.
How long does gesso take to dry?
Although gesso can be touch dry within one to two hours, depending on temperature, it’s best to wait at least 24 hours before painting on a gessoed surface. You should also wait at least an hour between coats. Keep in mind that sometimes humidity and temperature changes can affect the drying time of gesso.
What is sizing?
Sizing is the method of sealing the surface and forming a barrier layer between the support, and the ground and paint layers. When a layer of sizing is applied, it decreases the absorbency of the support. In the absence of this layer, the cellulose fibres of the support can soak up oil from the ground and paint, leading to it rotting.
If you’re using oil painting primer, you need to size your canvas with rabbit skin glue. Sizing needs to seal the surface and sit on the canvas to prevent anything going into the pores.
Can I prime canvas without gesso?
You can use other primers after sizing with rabbit skin glue. If you don’t prime or gesso your canvas it is likely to rot over time when directly in contact with your paint.
What is oil painting primer?
For oil paints, you can use an oil painting primer, a thixotropic or an oil-modified alkyd resin medium instead of gesso. Winsor & Newton’s ready-to-use oil painting primer doesn’t need thinning or stirring, and can be used on porous surfaces (glue-sized canvas, untreated wood, hardwood, plywood or paper) with virtually no sinking in. You can also mix a small amount of oil colour into it to make a tinted primer. But canvas needs to be sized before applying an oil painting primer.
What’s the difference between sizing and priming?
While sizing is about sealing the surface to protect your canvas, priming creates an even surface to work on. Oil primer offers a smoother surface, whereas thixotropic and acrylic primers offer more tooth.
How do I prime different types of canvas?
If you’re working with cotton duck canvas and want to use either oil or acrylic colour, an acrylic gesso primer is generally used, though you can use any of them.
If you’re priming a linen canvas, you can use an acrylic primer or an oil primer. Linen can be difficult to prime and stretch properly if it is a heavier-weight canvas because it is harder to fold neat corners around the stretcher with heavy canvas, but if you can master this process, you’ll benefit from the smoothest and stiffest painting surface. You can learn more about the difference between cotton and linen canvas in this article.
What is pre-primed canvas?
You don’t have to size and prime a canvas yourself. Winsor & Newton offers acrylic-primed cotton and linen pre-stretched canvases in different depths and sizes. If you want to avoid priming but prefer to stretch your own canvas, you can opt for rolled cotton canvases that come ready primed, though you’ll need canvas pliers to help stretch it onto your stretcher.
Canvas boards are another option, especially if you’re just getting started with oils, or have more experience but want a surface for studies. They are made of stretched and primed cotton canvas, adhered to a stiff backing.
Can you gesso over oil paint and reuse the canvas?
No – you can paint over old paintings but not re-gesso or prime over oil. If you have an acrylic painting you no longer want and you would like to reuse the canvas, start by lightly sanding the work to make the surface even. Then you can paint over it with gesso, before starting again with a new painting.
What is underpainting? Is it different to priming?
While priming prepares the canvas ready to receive paint, underpainting is a first layer of paint applied after priming. Traditionally a lean layer with a reduced palette, it’s a tonal rendering of the eventual painting that serves as a base for the full colours and layers that follow. Underpainting helps you work out your composition, and when toning a ground it is helpful to not have to work on a white surface. Some artists also find it useful because it’s easier to get started on a painting without the distraction of a bright white surface.
Artist have traditionally used a range of palettes for grounds. For example, the method of imprimatura uses earth tones, such as umbers and siennas, while grisaille uses grey paints. Verdaccio underpainting is done using grey-greens and olives.
What is a good white for underpainting in oil colour?
Winsor & Newton’s Underpainting White is made with linseed oil, rather than safflower oil. This means it dries much faster than other whites, allowing you to avoid the issues with cracking that might arise from using a slower-drying white, such as Titanium White, as a base coat.
