Painting in Oils

Thinning your Paint

As to how you actually apply your oil paint, ou can of course apply your paint straight out of the tube, but it will be stiff and dry. If you want to paint very thickly in an ‘impasto’ style there are various mediums you can mix with your paint and we’ll cover impasto painting in more depth further down. If you don’t plan on painting with very thick paint them you will want to dilute your paint a little to create the right flow. Some form of spirits (solvents) are traditionally added to thin down oil paint, and various types of oils may also be added to extend it and to help it to flow. You’ll need to learn a little bit about how to balance the two.

For centuries the traditional spirit for diluting oil paint was turpentine and you can still buy this but it’s pretty toxic and most people prefer to avoid it. If even artists’ white spirit gives you headaches or you are particularly concerned about toxicity then there are low odor products...

Alternatively, you may choose to dilute your oil paint with the addition of extra oil in order to create thin glazing layers, to increase the glossiness of your paint, or to either speed up its drying time or slow it down in order to manipulate the paint for longer.

Linseed oil is the classic choice for oil painting but can be a little yellowing and so safflower, walnut or poppy oils are a better bet for whites or pale colours. Linseed generally slows down the speed at which your paint will dry, but modified Fast Drying linseed or poppy oil will speed it up. Stand oil is a thickened linseed that is good for making even, smooth glazes. A popular product by Winsor & Newton called Liquin is an alkyd-based solution designed to dilute oil paint and increase its drying speed and viscosity. Liquin isn’t an oil (alkyds are oil-modified resins, fast drying and semi-matt) and also contains a small amount of solvent but it is designed to perform more like an oil medium than a solvent thinner. It’s more suitable for use on upper layers of a painting rather than underlayers where it should be used sparingly.

Coloured backgrounds/ toning layers

There are a number of reasons why you might want to add a tinted background layer to your painting. Faced with a dazzlingly white canvas and particularly if you are doing any kind of figurative painting from observation, it can be really hard to judge tonal relationships and colours. Therefore many people like to start off with a layer of colour whose tone equates to the mid-tone values of whatever they are painting.

There are other potential benefits to adding a coloured background. If applied over the entire painting, an underlying toning colour can impart a warmth and tonal unity to the layers above it by reflecting or revealing it through subsequent layers of semi-opaque paint or scumbled paint. Traditionally artists often covered their priming layer with a layer of thinned down paint called an Imprimatura. This would stain the pale coloured priming ground in order to create a mid-toned background which would unify the colours applied above it, creating an overall tonal atmosphere and a depth and vibrancy. Imprimaturas were often applied in an earth colour to impart a warm tone but you could also apply a background layer in a neutral grey or a cooler shade with some blue in it.

Another option is to block in large areas of different flat colours to define the different elements within your painting, rather than one single colour across the whole canvaas. This was a method often employed by the Impressionists and was close to the Ébauche method of underpainting.

The first paint you apply on top of the white priming layer will dry more slowly than subsequent layers, which will sink into those beneath them. Therefore you should apply your paint quite thinly and work it well into the canvas with your brush or you’ll be waiting well over a week for it to be touch dry. There’s no need to add extra oil to this paint layer because it will be absorbed by the priming below which has plenty of oil in it, and because following the Fat over lean rule you’ll want to avoid excess oil in your first layer of paint.

Reading Paint Labels

You don't have to guess the opacity of your paints; manufacturers print this information directly on the tube. Standard symbols usually include:Solid Square: Opaque (heavy coverage).Half-Filled Square: Semi-transparent or semi-opaque.Empty/Open Square: Transparent (ideal for glazing).

How Pigments Behave

Opacity is determined by pigment particle size and how light refracts through the dried binder.

• Opaque Colors These pigments (e.g., Cadmium Red, Titanium White, Cerulean Blue) scatter light and physically hide whatever is underneath. They are best for blocking in base shapes, underpainting, and creating a sense of a form "advancing" toward the viewer.
• Transparent Colors These pigments (e.g., Ultramarine Blue, Transparent Red Oxide, Viridian, Alizarin Crimson) allow you to see the details of underlying layers. They naturally "recede" and provide depth, glow, and luminosity.

One major visual difference between the two types of paints is how light comes back to your eye from the painting surface. With opaque paints, the light hits the surface of the paint and bounces back to your eye. Transparent paints operate more like a sheer veil of color. The light will hit the paint and since it’s transparent, will penetrate through to the ground (whether white watercolor paper or a white canvas) and will bounce back thru the transparent paint and back to your eye. In this way, it is like backlighting, which gives transparent paints their luminosity and glow.

In my own painting, luminosity and clean, bright color is important, so I generally start exclusively with a transparent wash/underpainting. This allows me to keep the color clean and avoid mud. I share this method in my workshops and go into greater depth on the topic in my instructional video, “Vibrant Flowers,” available through PaintTubeTV.

Opaques have the benefit of coverage with heavier body to create thick, impasto strokes. Transparents can provide contrasting thinner passages, and allow you to optically mix, since you can see one color through another.

For example, if you lay a transparent blue, like ultramarine blue, over a yellow, you will see green. The transparent blue will not totally cover what’s beneath it. Transparents are often very dark in mass tone. When two are mixed together, you can get some really dark darks. Yet when white is added to a transparent paint, it can act as high chroma opaque. Try adding a touch of white to transparent phthalo green, permanent rose, or Indian yellow.

(From A Quick Guide to Transparency and Opacity)

Key Techniques

Knowing when to use opacity versus transparency will drastically improve your artwork's realism and lighting.

• Glazing To create rich, glowing shadows (like a glassy ocean or a deep red fabric), you apply thin layers of transparent paint over a dried, lighter underpainting. The light passes through the transparent layer, hits the underpainting, and bounces back, creating intense luminosity.

• Impasto Opaque paints are excellent for thick, textured brushwork that physically stands off the canvas. Because they block underlying colors, you can carve out bright highlights (like glistening water or bright clouds) without the previous layers bleeding through.

  Analogously, scumbling involves lightly dragging an opaque paint (usually dry, with very little medium) over a darker underlying layer. It allows the opaque strokes to break up, creating atmospheric texture like mist or highlights on skin.

• Optical Mixing Layering thin, transparent and semi-transparent colors (instead of mixing them directly on your palette) creates a vibrant effect. The colors visually blend in the viewer's eye, resulting in cleaner, brighter hues.

How to Adjust Opacity

If a color is too transparent, you can increase its opacity by mixing it with an opaque counterpart of the same color or adding an opaque white. However, keep in mind this will change the hue and tinting strength. To decrease opacity, mix in more oil medium or use the paint in thinner, lighter layers.

Types of canvas

You’ll need to choose between working on a traditional stretched canvas, a canvas board or a canvas panel. Boards and panels are designed to be more cheap, lightweight and transportable and are generally intended either for practice paintings, or for painting out of doors.

Canvas boards are available in multipacks and are great for sketching and experimenting on, but because they are usually fairly flimsy and made from non-archival materials, they are best avoided if you want the work to produce to last in good condition for years. Panels are made with harder boards of some description and may be made with archival glue to protect the canvas from the acid in the panel – check the label to see if it is acid-free.

If you buy a regular stretched canvas you’ll need to choose between a cotton duck canvas (from the Dutch work doek, meaning cloth) and a linen canvas. Linen canvases have a tighter weave and are particularly elastic and strong, making them popular with many professionals. This doesn’t mean that they are superior to cotton or that there’s anything wrong with a cotton canvas, and indeed you might prefer the coarser texture of cotton.

Once you’ve decided between cotton and linen you’ll need to choose between an extra fine, fine, medium or rough weave. This is really a matter of personal choice. If you want to do finely detailed painting a smoother weave will suit you better, whilst if you want to do loose and expressive work you might like to see and actually emphasize the canvas texture.

If your canvas feels a bit slack and not springy enough, use the little canvas keys that come in a small back stapled to the back of your canvas to tighten it up.

Sizing and priming

Pre-stretched canvases should always come fully sized. Sizing is the practice of coating the canvas with either a rabbit skin glue, an acrylic polymer size or a PVA solution in order to seal the fibres of the canvas, protecting them from acids in the oil content of the paint preventing them from rotting as the paint slowly dries.

Most commercially stretched canvases will also be pre-primed, giving you a bright white finish that’s ready to work onto. Priming provides additional protection for the fibres and also provides a smoother surface, tightens the canvas, and encourages good adhesion of the paint layers. You don’t absolutely have to work onto a primed canvas as long as it is sufficiently sized, and some people like to work in a sketchy manner onto a plain canvas background which they allow to remain visible. If you want to work onto an unprimed canvas there are some stretched linen canvases available which are pre-sized with glue but not primed. These are typically referred to as glue sized canvases.

Priming is a slightly confusing area. Most prepared canvases will state that they are Triple primed with three layers of gesso which actually means that they have been primed with a universal acrylic-based primer suitable for painting with either oil or acrylic paint. This type of priming often known as Acrylic Gesso but has nothing to do with real gesso, which is a traditional mixture of glue size and gypsum. Sometimes it is just described as Universal primer. Some serious oil painters think it’s better to work on a canvas that has been prepared with an oil based primer rather than an acrylic one and prefer to buy oil primed linen canvases which are available at a price. However many painters are perfectly happy with a universally-primed canvas although some will give their canvas an extra coat of primer if they feel the priming layer is too thin and the canvas lacking in tautness and too absorbant.