How to varnish an oil painting: when it is dry enough, retouch varnish and storage

TUREFF• •0

Varnish protects an oil painting from dust and dirt, evens out shiny and dull patches, and can deepen the colours. Applied at the wrong time, though, it can trap soft paint underneath and stay sticky for a long time. Here is how to decide when, how and what to use, and how to store work while you wait.

Why varnish at all?

Protection: dirt, grime and smoke settle on the varnish, not the paint. A good picture varnish can be removed and replaced by a conservator decades later without touching the paint.
An even surface: oil paint dries with some areas glossy and some dull ("sinking in"). Varnish unifies them.
Colour: dark colours that have dried dull often regain their depth.

How long to wait before final varnishing

The paint must be dry right through, not just on the surface, because a solvent-based varnish on paint that is only touch dry can mix into the top of the film and stay tacky. Typical guidance from paint makers is in the range of several months to a year, and longer for thick paint. One manufacturer suggests at least six months for very thin paint, around a year for normal layers, and longer for thick impasto. Others give shorter windows for thinly painted works. Because advice varies, follow the instructions for the varnish you buy and use a physical test:

Press a fingernail gently into the thickest area of paint, somewhere it will not show. If it feels firm underneath, it is likely ready. If it gives or dents, wait.
When in doubt, wait longer. Waiting does no harm; varnishing too early can.

Retouch varnish

A retouch varnish is a thin, temporary varnish. It is used:

to bring back the colour in areas that have sunk in while you are still painting, so you can judge colours;
as a temporary protective coat on a painting you need to show or sell before it is dry enough for a final varnish.

Retouch varnish is generally applied once the paint is touch dry, often a few weeks to a couple of months on, depending on the maker's guidance. It does not replace the final varnish, which still goes on once the painting has fully dried.

How to varnish

Clean the surface: dust gently with a soft, clean brush or a lint-free cloth.
Choose a dust-free, well-ventilated room, ideally neither cold nor humid. Many varnishes contain solvent, so ventilate as you would for painting, or more.
Lay the painting flat so the varnish does not run.
Use a wide, soft, clean brush kept only for varnish.
Apply thin, even strokes in one direction, working across the painting in sections without going back over areas that have begun to set.
Let it dry flat, covered loosely (for example with a box lid raised above it) to keep dust off.
A second thin coat, if needed, goes on once the first is dry, often in the other direction.

Gloss, satin and matt finishes are available; matt varnishes can make dark colours look slightly cloudy if applied thickly.

Storing paintings while they dry

Keep them upright, with air around them, not stacked face to face. Even touch-dry paint can stick to whatever presses on it.
Keep them in some light: linseed oil paint kept in the dark can develop a yellowish film. It often fades again when the painting goes back into light.
Avoid damp, heat and big temperature swings: not in a loft, garage or against a radiator.
Store wet canvases where they cannot be knocked, with the painted side facing a wall but not touching it, or in a simple drying rack.

Storing finished paintings long term

Cover loosely to keep dust off, using something that does not stick to the surface, such as glassine paper, and avoid bubble wrap directly on the paint.
Store canvases upright, separated by stiff board, and lean them against each other back to back or face to face only with protection between.
Keep them in a dry room with a steady temperature.

How long do you wait before varnishing, and what have you used? Share your routine in the comments.