Oil painting varnish techniques 

You’re just finishing an oil painting. The million dollar question is: should you now varnish it? In this article, we address this question, as well as looking at different types of oil painting varnish and how to apply them to your artwork. 

Is it necessary to varnish an oil painting? 

You don’t have to vanish your finished oil painting; however, varnish can enhance the appearance of your work as well as adding an extra layer of protection, so it’s always worth considering. Here’s why varnishing your oil painting is a good idea. 

• Varnish adds depth to an oil painting and increases the saturation of the colours.  

• It evens out the finish of the painting – for example, if some areas look duller than others, varnish will create a more uniform effect. 

• Layers of varnish protect the oil paints from environmental damage caused by factors such as dust, dirt and smoke, and some varnishes are UV-resistant. 

• It’s easier to clean a varnished painting, and if you see an older oil painting that looks dull or discoloured, hopefully it’s the varnish that’s past its best rather than the paint. The restorer strips back the upper layers of varnish and reapplies fresh coats. 

If you’ve used decent-quality, slow-drying oil paint that’s been applied thickly onto a ​​properly prepared canvas, you don’t strictly need to varnish your painting. However, given all the reasons for using varnish that we’ve highlighted above, it’s worth the extra step. It’s also a pretty straightforward job. 

How long should an oil painting dry before you varnish it? 

And now here’s the bad news – it can take at least six months for an oil painting to be completely cured, depending on how thickly you’ve applied the paint. Even if the painting is touch-dry, which can take as little as two weeks, it’s still a long way from being ready for those coats of varnish. 

Why can’t you varnish a touch-dry oil painting? This is because oil paints are made from pigments dispersed in oil, which is dissolved in a solvent. The solvent evaporates as the paint dries, but the oil remains and oxidises, which is what causes the paint to harden. Oxidisation occurs when the oil reacts with oxygen, so the paint needs to have that exposure to air until this process is complete. If you varnish an oil painting too soon, the barrier between the air and the paint halts oxidisation, and the paint may never fully dry. 

What can you do if you’re working to a tighter schedule than that? Six months is a long time to hang onto a painting, especially if it’s a commission or is going into an exhibition. We’ll look at varnish types in a moment; however, there is a modern type of synthetic varnish that creates a permeable layer, allowing the oil to react with the air, post-application. 

Which varnish should I use? 

There are lots of different types of painting varnish on the market – how do you know what’s the best type of varnish for oil paintings (and yours in particular)? Here’s a quick run through some common types of varnish: 

• Traditional hard varnishes. Used by the Old Masters, these resin-based varnishes have certainly stood the test of time. These give a warm glow to the finish of the painting, but will eventually crack. They’re hard to get hold of these days, but have saved a lot of precious artworks from deteriorating over the centuries. 

• Traditional soft varnishes (like Dammar). These are also made of resin, but because they dissolve in solvents such as turps, they can more easily be removed. It brushes on nicely and gives the painting a soft and warm finish. 

• Synthetic spray varnish. If you’re new to the world of varnish, a spray is easier to apply than a more traditional brush-on version. (We’ll take you through how to do this shortly.) 

• Synthetic quick-drying finishes. This more recent innovation can be applied when the oil paint is touch-dry. As we mentioned earlier, this is ideal if you don’t have six months to wait! 

• Temporary varnish. This also allows the paint to continue drying, and has the great advantage that you can continue working on the painting after the varnish has been applied, which is a definite no-no with a conventional varnish. 

• Matte varnish. If you prefer a less glossy finish, choose a varnish that’s had wax added for a more matte finish. Matte varnish is better for abstract and impressionist artworks than for more realistic art styles. 

Look out for different types of varnish for oil and acrylic paints, and never use a varnish on watercolour. If you’ve used pencils or pastels, prevent smudges by using a fixative spray (which won’t work on paints). 

Do you need to add a layer of oil paint sealer before applying the varnish? No, you don’t, and this is because the oil paint and the varnish have such different compositions. If you’ve used acrylic paints, you do need to apply an isolation layer. The acrylic paint and varnish have a more similar composition, making it a highly risky business to remove the varnish unless there’s a protective layer in between the two.How to varnish an oil painting 

We’ll take a step-by-step look at varnishing an oil painting, using both brush-on and spray varnishes. For both methods, make sure you’re in a dry, well-ventilated and clean space. 

Varnishing oil paintings using a brush 

You’ll need a clean, wide brush that glides smoothly, along with a shallow dish to pour the varnish into. Lay or stand your canvas on a board so you don’t splash varnish onto your table or floor (and a clean board also reduces the risk of contamination). Always read the manufacturer’s instructions to find out exactly how to use the varnish, as most brands will vary slightly in method. 

1. Pour some of the varnish into the dish or tray, which makes it easier to transfer to the brush. 

2. Work quickly but gently, using long, smooth strokes. 

3. Apply the varnish top down, left to right, to make sure that you don’t miss any areas. 

4. If you do miss a bit, don’t go back over it now. Wait until the next coat. 

5. While the varnish dries, aim to prevent any dust or dirt sticking to the surface. Try placing props around the canvas (you can use anything, such as bricks or books) and put another board above the painting, close but not touching. This will help prevent dust or debris sticking to the varnish while still allowing it to dry. 

6. Check the instructions – how long should you leave it between coats? It can be up to 24 hours for a traditional brush-on varnish. 

7. Leave and repeat. It’s up to you how many coats of varnish you apply to your oil painting. If you want an intense glossy finish, this could be as many as 50 coats.  

How to varnish oil paintings using a spray  

Cold spray varnish doesn’t go on as well, so if it’s been stored in the shed or garage, bring it indoors well in advance. Make sure you have ventilation but that the space is free from draughts (you need to be able to control the direction of spray). 

1. Stand your canvas upright on a board. 

2. Shake the can of varnish for at least two minutes. 

3. Try and spray from an even distance – about 40cm is ideal. 

4. Leave 10 minutes in between each coat, and again, apply as many layers as you think you need. 

5. Keep checking the nozzle because spray varnish can become clogged up. If the nozzle is blocked, wipe it with a cloth and shake the can thoroughly again before you return to spraying. 

6. Check the manufacturer’s instructions for final curing time. 

Applying varnishes is a pretty straightforward task when you get the hang of it. However, should you need to remove a layer of set varnish from an oil painting, contact a professional restorer. Portrait artist Jonathan Yeo describes the “whole science around the longevity of paintings” and explains that he contacts the experts when he needs work doing.