During the drying process, an oil painting can sometimes lose it’s vibrancy a bit. It’s called ‘sinking’ and it occurs when the oil from the surface of the painting is absorbed by the layer underneath, therefore leaving the painting looking a bit dull. The darker the colour the more obvious it becomes. Often some areas sink in more than others, depending on properties of each individual paint and their different drying rates – and they vary quite a bit. Can this be fixed? Absolutely!
The painting has to be completely dry, otherwise there is a risk of damaging it. You will find that different artists prefer different methods and the opinions vary. The best practice is oiling out first and when the painting is completely dry again, apply a layer of varnish for protection.
The surface of the painting is saturated with linseed oil (or another suitable oil) to make up for the lost layer. After applying the oil carefully with a cloth (I sometimes find a soft brush easier, if the painting has a lot of texture) the excess oil is then carefully wiped off the surface and the painting is left to dry. It’s important not to leave any excess oil on the surface! This method is more natural and it does bring the colours back. It can be repeated in the future if needed, if you don’t varnish. However, it doesn’t protect the surface of the painting from dirt and dust, so applying varnish should always follow when it’s completely dry.
The advantage of varnishing your painting is that it not only brings the vivid colours back, but it also evens out it’s appearance and protects the painting from dust that naturally settles on the surface over the time. Most modern varnishes are removable, so if in the future your painting needs cleaning, the varnish can be removed and then a new layer can be applied again. And this is where the oiling out first is actually quite important. If you apply varnish to a badly ‘sunk’ painting, there is a risk of damaging it, if someone in the future tries to remove the varnish. Oiling out first will make sure the paint stays intact. Yes, this process takes longer, but if you want your painting to last for a long time, it’s quite necessary. Which brings me to the next point, which is: when should the varnish be applied?
When to varnish?
One disadvantage of varnishing is that your painting has to be absolutely bone dry, and it’s not recommended to varnish a painting sooner than 6 months after finishing it. A retouching varnish is an exception and can be apply once the painting is touch dry. It can even be painted on again. But this solution is only temporary and should be followed by a layer or two of a regular varnish to fully protect the painting when it’s ready for it. Which is what I do with my paintings. Once the painting is fully varnished, it should not be painted on again or cracking may occur.
What kind of varnish?
The varnish you use has to be of course a special oil painting varnish, not any kind of varnish. Always make sure it’s a good quality one and removable. Varnishes come with various different final effect. Gloss finish has a lot more reflections but really brings the colours out, while silky a matt surface might appear a little bit more dull. I have experimented with all options and now I create my own version by mixing a little bit of matt varnish into a gloss varnish. Just enough to take some of the glossiness off, while keeping most of the brightness.