A painting that may once have looked bright can, after several decades, appear noticeably brown, yellow or dull. Varnish is often blamed. But what exactly is varnish, how can you recognise a discoloured layer, and can it be removed safely? That last question in particular is more complicated than the dramatic difference between before-and-after restoration photographs might suggest.
A white collar that looks more ivory than white. A blue sky with a greenish cast. Shadow areas that gradually become so dark that they merge into brown masses. Such effects are common in older paintings that have spent many years hanging in private interiors.
One possible cause is surprisingly simple: it may not be the paint itself that has changed so dramatically, but a transparent layer lying above it. This is the varnish. Over the course of decades, varnish on older paintings can yellow, become cloudy or lose its gloss. This affects not only the colour of the surface, but also contrast, depth and the relationship between light and dark areas.
As a result, a painting can quite literally be read differently from the way the artist originally intended. Caution is necessary, however. Surface dirt, smoke deposits, old retouching, changes in pigments and binding media, and previous restoration treatments can all produce similar effects.
What is varnish on a painting?
Many oil paintings have a thin transparent coating above the paint layer. Varnish has two functions that are easily confused. The first is protection. To some extent, the coating separates the paint surface from dust, dirt and minor surface abrasion. Just as important, however, is its optical function.
A varnish layer can saturate colours and even out small differences in gloss across the surface. Dark colours gain depth, shadows appear richer and colour contrasts can become more distinct. This creates an interesting paradox: the same layer that can make a painting easier to read when it is fresh may begin to obscure it decades later.
Why does old varnish turn yellow?
Traditional natural resin varnishes in particular change as they age. They may yellow or even become brownish, grow brittle, develop cracks or take on a milky or cloudy appearance in certain areas. The extent to which this happens depends on factors including the type of resin used, the way it was prepared and the conditions in which the painting has been kept.[1]
Light plays a role, but this does not mean that a painting can simply be protected from ageing by keeping it in a dark room. Resins also undergo chemical changes over time. Slight yellowing may hardly be noticeable, whereas a heavily discoloured layer can substantially alter the overall colour balance.
Imagine placing a transparent yellow sheet over an image. Whites become warmer. Cool blues may appear greener. Subtle pinks and greys become harder to distinguish. Dark areas take on a brown cast. There is another effect as well: aged varnish can reduce the distinction between light and dark, which may in turn lessen the impression of depth. This helps explain the sometimes dramatic appearance of paintings during restoration.
How can you tell at home whether a painting has yellowed varnish?
Examine the painting in good, diffuse daylight and look at the surface from several angles. A general yellow-brown cast may be suggestive, especially if light areas appear unusually creamy and cool colours have lost much of their clarity. Areas that look cloudy, greyish or noticeably uneven in gloss can also indicate an aged surface coating.
None of these features proves that varnish is responsible. A grey or dull layer may simply be surface dirt. Paintings that have spent many years in houses where people smoked, used open fires or cooked extensively can accumulate substantial deposits. Discolouration may also occur within the paint itself. Some pigments and binding media change as they age.
Old retouching can likewise discolour, becoming darker or lighter than the surrounding original paint. Craquelure also tells us little about the condition of the varnish. Fine cracks in an old oil painting do not automatically mean that the work needs to be cleaned or restored.
How does a conservator know where the varnish ends?
A paintings conservator first examines the surface and overall condition of the work. Very small test areas are then used to determine how the various materials respond. The question is not simply whether the varnish dissolves. Just as important is how the paint layer reacts.
An appropriate cleaning system must affect the unwanted layer sufficiently without softening, dissolving or otherwise damaging the original paint. The response can vary even within a single painting. A dark passage may not behave in exactly the same way as a light flesh tone or a thinly painted sky.
Under magnification, the conservator can continuously monitor what is happening at the surface. With certain traditional resin varnishes, ultraviolet fluorescence can also help distinguish old varnish from some later retouching.[2] This does not mean that every restoration requires an extensive technical research programme. With many paintings in private ownership, careful observation, experience, localised testing and controlled treatment are what matter most.
Why can a painting suddenly look so much more colourful after restoration?
A blue sky that had looked grey-green for years may suddenly appear distinctly blue. A white shirt becomes genuinely white. Small figures that were barely visible begin to stand out from the background. This does not necessarily mean that anything has been done to the original paint. On the contrary, much of the visual change may result simply from removing material that was lying above it.
When a heavily yellowed varnish is removed, the yellow-brown filtering effect across the whole painting disappears with it. If a new, clear varnish is subsequently applied, the colours become saturated again. The painting may therefore look far more colourful without the conservator having repainted those original colours.
Retouching can, however, form part of a conservation treatment. Old damage, losses or earlier restorations that have discoloured badly may become clearly visible after cleaning. A conservator may subsequently retouch such losses locally. For that reason, the common statement that restoration simply “brings back the original colours” is somewhat too simplistic.
A painting that is two or three hundred years old has also aged beneath the varnish. Pigments, binding media and paint structures may themselves have changed. Restoration cannot turn the clock back to the day the artist put down the brush. It can, however, remove a strongly discoloured layer that interferes with our view of the surviving paint.
Why do some paintings have several layers of varnish?
With an old painting, it is often misleading to speak of the varnish layer. Many paintings have undergone repeated treatments during their lifetime. A work may once have been cleaned and revarnished. During a later restoration, some of the earlier varnish may have remained in place. Retouching can become sandwiched between different varnishing campaigns, and sometimes a new layer was simply applied over an older one.
Over the course of one or two centuries, a sequence may therefore develop consisting of original paint, old varnish, restoration material, new varnish and further retouching. For the owner, this is important because cleaning can reveal unexpected features. A well-preserved original paint layer may be hidden beneath dark varnish, but so too may old abrasion, discoloured retouching or overpaint.
Varnishes also come in different degrees of gloss. A glossier surface can strongly saturate colours and give dark areas greater depth. A more matt surface scatters more light and therefore changes the way the paint is perceived. The appropriate degree of gloss depends on the artist, period and painting technique.
Does every oil painting have varnish?
Many oil paintings are varnished, but certainly not all of them. Some are only partially varnished, while in other cases an unvarnished or matt surface formed part of the intended appearance.[3] It is also possible for a painting to have no varnish today even though one was present in the past, for example following an earlier restoration.
Can yellowed varnish affect the value of a painting?
Yes, but there is no simple one-to-one relationship between varnish and value. A heavily yellowed or cloudy coating can make a painting commercially less attractive because colour, contrast and detail become difficult to read. Condition reports issued by major international auction houses therefore regularly mention discoloured, cloudy or aged varnish separately.
A painting does not automatically become more valuable once that layer has been removed. A well-preserved paint surface beneath strongly discoloured varnish may benefit considerably from treatment. Cleaning, however, can also reveal old abrasion, losses and extensive previous restoration. For the market, the condition of the original paint is ultimately more important than the mere presence or absence of yellow varnish.
Anyone considering selling a potentially important painting would therefore be well advised not to commission extensive restoration on their own initiative beforehand. A qualified conservator can assess the condition, after which an art-market specialist can help determine whether treatment before a possible sale would be advisable.
When is an examination worthwhile?
A brownish cast alone is not an emergency. A painting can remain stable on the wall for decades despite having a discoloured varnish layer. Varnish removal is not a routine maintenance procedure that should be carried out periodically.
An assessment becomes particularly worthwhile when a painting has become noticeably dark or cloudy, when colours are difficult to read, when there are pronounced differences in gloss or when old restorations have visibly discoloured.
If the paint is lifting, flakes are loose, new cracks have appeared or actual material is being lost, the priority is different. The issue is then no longer primarily aesthetic, but concerns the physical stability of the painting.
Look first, treat later
Varnish is one of the more curious components of a painting. When it is clear, we barely notice it. As it ages, it can fundamentally alter the way we see the paint beneath. An old painting that appears dark, yellow or dull can therefore look surprisingly bright after professional treatment.
The surface we see may consist of paint, varnish, dirt, retouching and residues from earlier restorations accumulated over decades or even centuries. The first question should therefore never be: how can I clean this? It should be: what exactly am I looking at?
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Do you follow this artist, or have you come across a work you would like to know more about? We regularly research works appearing on the market and are always happy to exchange views on quality, provenance, art-historical context and previous auction results. You can contact us directly via info@antonello.art.
Notes and sources
[1] Canadian Conservation Institute, Caring for Paintings, section “Varnishes”. On natural resin varnishes, yellowing, differences between resin types and modern synthetic varnishes.
[2] The National Gallery, London, “Ultraviolet fluorescence”. Traditional natural resin varnishes such as mastic and dammar can show characteristic fluorescence under ultraviolet light; some later retouching may also become easier to distinguish.
[3] Canadian Conservation Institute, Know Your Paintings – Structure, Materials and Aspects of Deterioration.