Oiling out: how to fix sinking and dull areas in oil paintings

There are many aspects to oil painting that seem intimidating, with plenty of rules to follow and warnings about potential pitfalls. But there are also clever tricks that can help artists put things right if they go wrong, and oiling out is one of them. 
Read on for our expert answers to your frequently asked questions, and find out how to perfect this simple, yet highly effective, technique for oil painters. 

What is oiling out? 

Sometimes you may notice that an oil painting has become dull looking; it no longer glows and the colours appear less saturated. This is usually the result of what is known as ‘sinking in’ – something that happens when the top layer of oil has been absorbed by the layers underneath. When this happens, oiling out is the name given to the process of providing the painting with a new lease of life. 

What does oiling out do? 

Oiling out will immediately improve saturation and revive your painting. Once you’ve finished, you can start painting again straightaway, or wait for the surface to dry.

How do I oil out a painting?

We recommend oiling out using a mixture of stand oil and Sansodor (Winsor & Newton’s low odour solvent). A good ratio to start with is one part stand oil to four parts Sansodor. However, if you have added oil to your paint already, you should use a mixture with a greater proportion of stand oil, in order to follow the fat over lean rule (more on this later). Stand oil is ideal for this because the heating process it goes through means it’s rich and non-yellowing.

Make sure the oil and Sansodor are completely combined before you start applying the mixture. Then use a soft brush to paint it evenly across the surface of your painting. You’ll notice that where there are dull patches, the mix will be absorbed and instantly improve the appearance of the painting. Where it’s not needed, it will simply sit on the surface. Using a lint-free cloth, gently wipe this excess mixture away.

When you’ve finished oiling out, you can keep any remaining mixture in a carefully labelled jar. You’ll need this, because if you’re continuing to work on the painting, you’ll have to dilute your paint with the oiling out mixture from now on, adding more with each layer to ensure you follow the fat over lean rule. This video tutorial gives a demonstration of the oiling out process.

Why do paintings become dull?

As previously mentioned, the result of sinking in refers to when the earlier layers of your painting have drawn the binder (the oil in the paint) away from recent layers. An over-absorbent – or poorly primed – surface is one cause of sinking in: priming creates a protective layer that stops paint being absorbed into the weave, and without this the oil will sink. Problems also arise if you thin the paint in earlier layers with too much solvent, so they soak up oil from the layers above.  
Not following the fat over lean rule, by failing to ‘fatten’ the colour in the top layers of your painting with enough oil medium, can also causing sinking. Smaller dull spots can be a result of using paints with different drying rates, which creates a paint film where some areas are more absorbent than others.

Should you always oil out before varnishing?

You only need to oil out if you have areas where the colour has sunk.

Can you oil out a painting after it’s been varnished?

No. If you want to treat a dull area after varnishing, you will have to remove the varnish first, and then revarnish once you’ve finished oiling out.

Is sinking in a risk when painting alla prima?

Alla prima, also known as ‘wet-on-wet’ oil painting, or direct painting, is a technique in which fresh paint is applied alongside or over paint that’s still wet, rather than waiting for a previous layer to dry in the traditional way. It means a painting can be completed much more quickly (alla prima translates from Italian as a first attempt).

In some wet-on-wet painting, different paints are applied alongside each other, effectively making the finished piece one single layer. But if you paint anything on top of an existing layer, even if it is still wet, you create a separate layer, and sinking in remains a risk. Painting fat over lean is therefore just as important when working alla prima.

How is shrinking different from sinking?

Like sinking, shrinking can be caused by failing to paint fat over lean. If you don’t follow the fat over lean rule and paint a layer that is leaner than the one beneath it, it will dry faster and may shrink when it does, causing wrinkling and cracking (also known as craquelure, particularly when referring to older paintings).

Shrinking can also occur if you’ve laid oil paint on particularly thickly, using the impasto technique, and the outside of the layer cures first, while the paint beneath remains wet for longer.

What else can I use for oiling out?

Any oil-based medium can be used for oiling out. For dull spots, rather than whole areas of dullness, you can apply a small amount of Artists’ Painting Medium on a clean cloth. Rub it gently into sunken areas, wipe off any residue and leave it to dry for a day or two. If you can still see smaller dull areas, repeat the process until the painting has regained an even sheen.

For a faster-drying oiling out medium, use Thickened Linseed Oil diluted with fifty per cent white spirit.

You can also use Winsor & Newton’s Artists’ Retouching Varnish for oiling out, but it’s best to rely on this method only for localised dull areas. This product is ready to use, so you don’t need to dilute it – paint it on, and after five minutes the painting will be ready to work on again.

Explore oil painting mediums here.