Varnishing a painting protects the surface, and makes its surface consistent and glossy, like the top surface of a freshly finished painting. A coat of varnish can be taken off and replaced without destroying the top coat of the painting, preserving it for longer than an unvarnished work, with less damage from aging.

A painting will not be ready for varnishing until it is properly dry. As oils polymerise rather than drying by evaporation, this takes a very long time. In fact, ancient paintings are still very slowly changing. However, at some point there is enough stability to put a layer of varnish on. This is generally around the three to six month mark. I paint thin layers which dry well, so I usually varnish things at three months, but the time taken will depend on the paint in question as well as the paint depth. Anything white or light blue takes longer to dry because it needs a different oil.

The first thing to do is make sure your painting is clean and dry, and oiled out. (If you don’t know what that last thing means, hold fire on the varnishing.) If you had to clean dust off it, which could happen, give it at least a day to dry. Then lay it flat in an area with good lighting and find a wide, flat, dust-free brush. This is as close to painting a house as you’re likely to get, so live for the moment.

You’ll want glass varnish, and maybe matt varnish, but the first couple of coats should be gloss. That is less cloudy, and you can put any surface you like over it. Pour some into a flat bottomed jar, and start painting, from one edge to another. Go left to right first, and then top to bottom. If you’re getting air bubbles, you’re going too fast and you probably need more varnish. Once you’re done with that double layer, check it in the light. You should be able to see light gleaming from the texture of the canvas. If there are areas that have too much varnish, they will be one big glisten. It’s a bit harder to spot where the light isn’t in place enough, but take a good look.

Dry it. Your varnish will vary, but a coat every couple of hours does for me.

If you want a matt effect, add matt varnish to your gloss on the last layer, 50:50 or use just matt. That’s up to you, and you have to learn what you like most. Then you’re done.