Light dusting with a clean, soft, dry brush is the only cleaning you should carry out on an original painting. Everything else belongs with a trained conservator. Water, household cleaners, damp cloths and the folk remedies that circulate online all remove paint and varnish along with the dirt, and that loss cannot be reversed.
This is the piece of advice owners most often disregard, usually with good intentions, because a painting that has dulled looks like it needs a wipe. What is actually dulling it is generally a layer of aged varnish, and removing varnish safely is a solvent-based process that requires testing the specific surface first. This page explains why, and covers varnishing, which is the other operation owners are tempted to attempt.
Key takeaways
- Dry dusting with a soft brush is safe. Anything wet is not.
- A painting that looks dull is usually showing aged varnish rather than surface dirt, and that is a conservator's job.
- Oil paint keeps curing for months, so varnishing too early traps solvent and causes clouding or cracking later.
- The artist who made a contemporary painting is the right person to ask about varnishing it.
The only cleaning you should do
Take the painting down and work in good light. Use a clean, soft, dry brush kept for this purpose alone, and move it lightly downward across the surface so dust falls away rather than being pushed into the texture. Support the back of a stretched canvas with your other hand so the surface does not flex under the brush.
Do this once or twice a year. Dust the frame and the back at the same time, and check the reverse for insects or any sign of damp while the painting is off the wall.
That is the complete list. There is no second technique that is nearly as safe.
Why wet cleaning damages paintings
A painting is a stack of layers: a support, a ground, paint, and usually a varnish on top. Those layers are chemically related to the solvents in ordinary cleaning products, which is exactly the problem. A liquid that dissolves grime will also, given a few seconds more contact, begin dissolving what is underneath.
Water is not safe either. It can swell the canvas, soften certain grounds, and lift paint that has already begun to loosen. On unvarnished contemporary paintings, particularly acrylics, water can pick up pigment directly.
The remedies that circulate socially deserve naming, because they keep resurfacing: bread, saliva, potato, onion, olive oil, dish soap, baby wipes, glass cleaner. Every one of them causes documented damage, and several deposit residues that make later professional treatment harder and more expensive.
The result of a home cleaning attempt is rarely dramatic at the moment it happens. It is a slight lightening in one area, or a faint bloom, noticed weeks later, by which point the paint that came away on the cloth is gone permanently.
What professional cleaning involves
A conservator begins by examining the painting under magnification and ultraviolet light to identify the varnish, any earlier retouching, and areas of instability. They then test solvents in a tiny inconspicuous area, working from the weakest, and observe how the surface responds before touching anything visible.
Only then does cleaning begin, worked in small sections under magnification. Where old varnish is removed, a new stable varnish is usually applied. Any losses are filled and retouched with materials chosen to be removable later, which is a defining principle of modern conservation: today's treatment must be reversible by whoever handles the painting next.
Ask a conservator for a written condition assessment and an estimate before agreeing to work. Ask what will be removed, what will be added, and whether the treatment is reversible.
Varnish: what it is for
Varnish is a clear removable coating applied over finished paint. It gives the surface an even sheen, saturates the colours so they read as the artist intended, and acts as a sacrificial layer: dirt settles on the varnish rather than in the paint, and a conservator can remove and replace it decades later without touching the painting itself.
Not every painting is varnished, and that is often deliberate. Many contemporary artists prefer a matte, unvarnished surface, and some acrylic works are left bare as a choice about how the piece should look. An unvarnished painting is not an unfinished one.
When an oil painting should be varnished
Not until the paint has fully cured. Oil paint dries by oxidation rather than evaporation, a slow chemical process that continues long after the surface feels dry to the touch. Thin passages cure faster than thick impasto, so a painting can be touch-dry in days while parts of it are still curing months later.
Varnishing over paint that has not finished curing seals in solvent that still needs to escape. The consequences appear later as clouding, a milky bloom, or cracking in the varnish layer, and correcting them means removing the varnish, which is a conservator's job.
Because the correct interval depends on paint thickness, medium and conditions, there is no single number worth quoting here. The reliable answer for a contemporary painting is to ask the artist who made it, since they know what they used. Many artists supply work already varnished, in which case nothing is needed.
Acrylic paintings are a separate case. Acrylic dries quickly, but varnishing acrylic uses different products and often an isolation coat first, and the reasoning does not transfer from oil.
What to do about specific problems
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The surface looks dull or yellowed. Almost certainly aged varnish. A conservator can remove and replace it. Do not attempt this.
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Paint is lifting or flaking. Stop touching it, keep the painting horizontal and still, and call a conservator. Flaking accelerates once it starts.
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There is a tear or a puncture. Do not tape it, from either side. Adhesive tape damages paint and leaves residue that complicates repair.
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There is mould. Isolate the painting from others, get the humidity down, and call a conservator. Wiping mould spreads it and drives spores into the surface.
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Something has been spilled on it. Do not wipe. Blot nothing on the painted surface. Photograph it and contact a conservator immediately, since speed genuinely helps here.
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There is soot or smoke damage. A specialist problem, and one of the situations where an attempted home clean does the most harm, because soot smears into the surface.
Frequently asked questions
Can I clean an oil painting with soap and water?
Do not clean an oil painting with soap and water. Water can swell the canvas and soften the ground, and soap will begin lifting varnish and paint after only a few seconds of contact. The damage is usually subtle at the time and permanent, appearing as slight lightening or a faint bloom weeks later. Dry dusting with a soft brush is the only safe cleaning an owner should do.
Why do people say to clean paintings with bread or a potato?
These remedies circulate because the material picks up loose surface dust and the painting briefly looks better, which is mistaken for a successful clean. In practice bread, potato, onion and saliva all deposit starch, moisture and organic residue on the surface, which attracts more dirt and can encourage mould. They also make later professional treatment harder and more expensive.
My painting looks dull. Does it need cleaning?
A painting that has dulled is usually showing aged varnish rather than surface dirt, because varnish yellows and clouds over decades. That is a conservator's job, since removing varnish requires identifying it and testing solvents on the specific surface first. Dusting will not change a dull appearance, and if dusting makes no difference, the cause is under the surface rather than on it.
How long should I wait before varnishing an oil painting?
Wait until the oil paint has fully cured, which takes considerably longer than it takes to feel dry, because oil dries by a slow chemical reaction rather than by evaporation. Thick impasto cures far more slowly than thin passages, so no single interval applies to every painting. For a contemporary work, ask the artist who made it, since they know the paint and mediums used.
What happens if a painting is varnished too early?
Varnishing an oil painting before it has cured seals in solvent that still needs to escape, and the result appears later as clouding, a milky bloom, or cracking in the varnish layer. Correcting it means removing the varnish, which is a conservator's task and costs more than waiting would have. This is why patience is the standard advice from every conservation source.
Does every painting need varnish?
Not every painting needs varnish, and many contemporary works are deliberately left unvarnished because the artist wanted a matte surface. Varnish provides an even sheen, saturates colour, and gives a removable sacrificial layer that collects dirt instead of the paint. An unvarnished painting is a finished painting, and adding varnish to one that was meant to be matte changes how the artist intended it to look.
Can a conservator remove old varnish safely?
A conservator can usually remove aged varnish safely, working under magnification after testing solvents in a small inconspicuous area to see how the specific surface responds. Modern conservation practice requires that any treatment be reversible by whoever handles the painting next, so replacement varnish and any retouching are chosen to be removable. Ask for a written assessment and estimate before work begins.
What should I do if my painting gets torn?
If a painting is torn, do not apply tape to either side, because adhesives damage paint and leave residue that makes repair harder and more expensive. Keep the work flat and still so the edges of the tear do not move against each other, photograph it, and contact a conservator. Tears in canvas are routinely repaired, and the outcome is much better when nothing has been attempted first.
How do I clean the frame without touching the painting?
Dust a frame with a soft dry brush or a barely damp cloth used only on the frame itself, keeping well away from the edge where frame meets painting. Never spray any product near a painting, since aerosol drift settles on the surface. For gilded or ornate frames, use only a dry brush, because moisture lifts gilding and water marks it permanently.
Is it safe to clean a painting behind glass?
Glazing over a work on paper can be cleaned, but spray the cleaner onto the cloth rather than onto the glass, so nothing runs down into the frame where it can reach the artwork. Do not press on the glass, since pressure can transfer to the work beneath. Where the glass has broken, keep the frame horizontal and take it to a framer rather than removing shards yourself.
Sources and references
Each link was opened and confirmed to resolve on 5 September 2026.
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Storage and Display Guidelines for Paintings, CCI Notes 10/3. Canadian Conservation Institute, Government of Canada. Published 1986, revised 2016. Accessed 5 September 2026.
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Condition Reporting, Paintings. Part II: Examination Techniques and a Checklist, CCI Notes 10/7. Canadian Conservation Institute, Government of Canada. Accessed 5 September 2026. Source for the examination approach described under professional cleaning.
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Environmental Guidelines for Paintings, CCI Notes 10/4. Canadian Conservation Institute, Government of Canada. Published 1990, revised 2016. Accessed 5 September 2026.
No specific curing interval for varnishing is stated on this page because it depends on paint thickness, medium and conditions, and any single figure would be a guess. Ask the artist who made the work.
