Varnish on a painting: when to apply it and why
Table of contents
A buyer who learns that a painting is not yet varnished often takes it for unfinished work. In fact it is a technical necessity, and haste does more harm here than waiting.
Here is what varnish does and why it is applied after a year rather than after a week.
What varnish does
Two functions, both important.
Protection. The varnish layer takes on dust, soot, light contact and airborne pollution. In decades, when it darkens, a conservator removes it with solvent and applies a new one — and the painting beneath remains untouched. Without varnish all of that would settle directly on the paint and could not be removed.
Optics. Oil paint loses saturation unevenly as it dries: some pigments go matte more than others, and the work becomes patchy in sheen. Varnish evens out the surface and returns to the colours the depth they had when wet.
The difference is immediately visible. The same work before and after varnishing looks as though it had been repainted.
Why not straight away
Oil dries not by evaporation but by oxidation: the oil absorbs oxygen from the air and polymerises. The process is slow and proceeds from the top down — the upper layer hardens first, the lower ones go on reacting for months.
Cover the work with varnish too early and the oxygen supply is cut off. The lower layers never fully cure, and years later cracks appear — the paint under the film behaves differently from the film above it.
The timing depends on the thickness of the paint.
| Type of work | When to varnish |
|---|---|
| Thin layer, glazes | from 6 months |
| Medium density | 8–12 months |
| Impasto, thick paint | up to 18 months |
A simpler rule than the table: wait until the surface no longer smells of oil and solvent. While the smell is there, the process is running.
What to do with an unvarnished work
Nothing special. The work is entirely fit to hang and to look at.
It is only somewhat more vulnerable to dust — so remove it every few months with a dry soft brush. Washing or wiping with anything damp is out of the question; that applies to varnished works too, but on an unvarnished one it is disastrous.
The conditions are the same: no direct sun, no proximity to a radiator, stable humidity.
Who applies it
Not the owner. This is not a case for doing it yourself.
Varnishing requires an even layer, the right varnish for the particular painting, a dust-free surface and a room without draughts or dust. A mistake here can only be undone by removing the whole layer with solvent — and that is already conservation work.
In practice it is done either by the artist or by a conservator. If you bought the work at the studio, the simplest course is to bring it back after a year — or to arrange a specialist to do it on site.
Types of varnish
Not for the buyer to choose, but useful for understanding a conversation with a conservator.
Dammar. A natural resin, the classical option. Gives a warm tone and good depth. Downside: it yellows more noticeably over the years than synthetics.
Mastic. Also natural, softer than dammar. Yellows more still, so it is less used now.
Synthetic. Acrylic and ketone resins. They do not yellow, or yellow minimally, and come off more easily. The current standard for most works.
Matte, satin, gloss. Not a matter of taste but of the work: dense impasto under gloss begins to reflect unevenly, so matte is better there. A smooth glazed work, by contrast, gains from gloss.
When to renew
After twenty to forty years varnish darkens and yellows. That is a normal part of its job: it ages instead of the painting.
A conservator removes the old layer, cleans the surface and applies a new one. The painting beneath does not change — provided the varnish was of good quality and comes off as intended.
This is exactly why museum works of the seventeenth century look fresh. Not because paint does not age, but because the varnish over it has already been changed several times.
Frequently asked questions
Can an unvarnished painting be hung?
Yes. The work is entirely fit to display, merely a little more vulnerable to dust. The essentials: do not wash it, do not wipe it with anything damp, and remove dust with a dry soft brush every few months.
Who pays for varnishing if the work was bought fresh?
This is agreed at purchase. Often the artist takes it on — the buyer brings the work back after a year and it returns varnished. Worth settling in advance.
Can I apply varnish myself from a spray can?
Technically yes, in practice better not. Spray varnish gives an uneven layer, and a mistake can only be corrected by removing the entire coating with solvent. That is conservation work and costs more than proper varnishing.
How do I know the varnish needs renewing?
The surface turns yellowish, whites and cool passages go dull, a general haze appears. It happens slowly, so it shows when compared with a photograph from ten years ago.
Works from the studio are handed over with guidance on when they should be varnished. If you have questions about a particular canvas, write to me.
