Varnish is the final protective layer added to a completed oil or acrylic painting. They can also help to enhance the painting once it’s dry. You can varnish an acrylic painting as soon as it’s dry, but it’s best to wait at least 10 weeks before varnishing an oil painting as the paint will take a long time to cure sufficiently.
There are lots of different types of varnish to choose from so I’ll explain the main differences between varnishes and what you should think about when picking the right type.
Varnish comes in different types of finish. Different types of paintings and personal preference affects what type of finish you need.
Gloss: Traditional representational paintings usually opt for a gloss finish because the smooth surface ensures that the colours are rich and the blacks are deep.
Matte: Whereas more textured abstract painting will generally look better with a matte varnish as it can look messy of the surface is too glossy. It is always best to use a varnish as they are important for protecting the painting’s surface so if you don’t want the varnish to be apparent, then a matte varnish is the best option.
Satin: Satin varnish is a good compromise and tends to suit more modern, figurative or semi abstract work.
Spray vs Brush-on
Spray varnish comes in an aerosol can (like spray-paint) and is very easy to apply thinly and evenly. Whereas brush-on varnish comes in a bottle and needs to be applied by brush. In general I would opt for spray varnish as it always results in a nice even coat. However there are some instances where brush varnish can work better, usually when a very glossy finish is required. This is because liquid varnish can be applied in a much thicker layer, so if it is glossy, it can achieve an almost glass-like finish quite quickly.
Soft vs Hard
Modern synthetic varnishes are usually hard, which means they can’t be easily dissolved and removed once they’re dry. Hard varnishes are easy to maintain and do a good job of protecting the painting surface.
Some traditional varnishes are soft, which this means that they can be dissolved once applied. This can be useful for cleaning purposes and they were often used in traditional painting practices because it was possible to remove them after several centuries of collecting dirt. A new layer of varnish would then be applied to replace the removed layer.
The most common way to use a soft varnish is to layer it over a hard varnish. This way the top layers of the painting are protected by the hard varnish while the soft varnish can be removed to get rid of dirt.
Applying, Drying and Layering
Always look at the guidelines and safety warnings on whichever varnish you choose to use. It is best to varnish in a well ventilated area because they are often quite toxic (particularly when sprayed) before drying.
Let the varnish dry in the most dust free and still environment you can find, otherwise it will gather dust. If the varnish is applied quite thickly, you will need to let it lie flat for a while so that the varnish doesn’t run down the surface and streak while drying (this is usually more of a concern with brush-on varnish).
Always apply varnish in reasonably thin layers so that they dry fully before applying more. Otherwise there is a risk that the varnish will take a long time to dry and there is a risk it will collect dust and dirt in the meantime.