How to Varnish an Oil Painting (and When)

Why varnish at all

A final varnish does three things. It evens out the gloss across the surface (oil paint dries unevenly, with some passages sinking in and others remaining glossy). It saturates the colour so the painting reads the way you intended. And it provides a removable layer that protects the paint from dust, smoke, and minor surface damage.

The keyword is removable. A good final varnish can be safely taken off in fifty years for cleaning. A bad varnish becomes part of the paint film and ages with it, often badly.

When the paint is actually dry

Oil paint dries in stages. Touch dry happens in days. Surface dry happens in a few weeks. But full curing, where the entire paint film has oxidised through to the support, can take six to twelve months for a normally painted work and longer for a thickly impasto-ed surface.

The traditional rule for final varnish is six months minimum, twelve months ideal. Varnishing too soon traps solvent and un-cured oil under the film, which can lead to:

• Cloudy or milky patches that never clear.
• A varnish film that sinks into the paint and refuses to come off without taking pigment with it.
• Yellowing that is locked under the varnish layer.

If you absolutely need to varnish sooner (for an exhibition, for example), use a retouch varnish first and apply final varnish later.

Retouch varnish

Retouch varnish is a thinned varnish designed to be used on partially cured paintings. It saturates the surface, evens out dull patches, and is easily removed by a final varnish later. It is the right tool when:

• You need to ship a painting before the six-month mark.
• You are exhibiting recent work and want an even surface.
• You plan to continue working on the painting and need to revive a sunken passage.

Retouch varnish is not a final varnish, and it should not be treated as one. Note in your records when you applied retouch and plan to apply final varnish later when the paint has fully cured.

Choosing a varnish

The two main families of artist varnish:

• Natural resin (damar, mastic). Traditional, beautiful saturation, but yellows over time and gets harder to remove safely. Conservation-aware painters increasingly avoid these for final varnishing.
• Synthetic resin (Gamvar, MSA, Regalrez 1094). Modern, more stable, less yellowing, and easier to remove cleanly with mild solvents in the future. Preferred by most contemporary conservation guidance.

Within either family, you can choose a finish:

• Gloss. Fully saturates colours and brings out depth. Best for traditional representational work.
• Satin. A compromise that reduces glare without losing colour saturation. Often the safest middle ground for a working artist.
• Matte. Reduces glare most aggressively but can dull deep colours and look chalky. Better used as a final coat over a gloss base if you need a matte finish.

Brush or spray

Both work, and each has trade-offs.

Brushing gives you the most control and uses the least varnish. Use a wide, soft, clean brush kept exclusively for varnishing. Apply in a single direction first, then cross-hatch lightly to even out the layer. Avoid going back over a section once it has started to set; you will leave brush drag marks and matte streaks.

Spraying gives a more even film and is the only practical option for very textured surfaces or large works. It requires either an aerosol can or a low-pressure sprayer, good ventilation, and a dust-free environment for several hours after.

Whichever method you choose, varnish in a clean, well-lit room with the painting flat. Dust is the enemy. Vacuum the floor an hour before, close the windows, and let the air settle before starting.

Common mistakes

• Varnishing too thick. Thin coats are easier to remove, dry more evenly, and look better. Two thin coats beat one heavy coat.
• Varnishing in cold or humid conditions. Aim for room temperature and dry air. Varnish applied in damp conditions can bloom milky.
• Treating retouch varnish as final. It is not, even if it looks good for a year. Apply final varnish when the paint is genuinely cured.
• Varnishing acrylic paintings with oil varnish. Acrylic paintings need acrylic-compatible isolation coats and acrylic varnish systems. Mixing them creates problems for future conservation.
• Not noting it anywhere. Twenty years from now no one will remember what was used on the painting unless you wrote it down.

What to record

For every painting you varnish, note:

• The varnish brand and product name.
• The finish level (gloss, satin, matte).
• The date applied.
• Whether it was retouch or final.
• How it was applied (brush, spray, number of coats).

Five lines of notes per painting. Future you, the buyer, and any conservator who ever touches the work will thank you.