How Conservators Retouch Old Paintings

A good touch-up adds nothing the artist did not paint.

When an old painting loses flakes of paint, conservators fill the gaps so the eye reads the picture, not the damage. The rules are strict: new paint goes only into losses, in materials that can be removed again.

Updated 16 October 2026 · 5 sources

Fill only the losses
Use paint that comes off
Leave a trail
The conservator's rules

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THE SHORT ANSWER

Restore the picture,
not the past.

Retouching hides damage, not history.
Three rules keep it honest.

WHERE

Only into the losses

The AIC defines inpainting as new paint put into areas of loss, and only into areas of loss. It should never alter the original.

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HOW VISIBLE

Invisible, or honest?

Methods like tratteggio fill a loss with fine lines that read as whole from afar but can be told apart from the original under scrutiny.

Why it matters

WHEN IT GOES WRONG

A flood, and 50 years

Vasari's Last Supper sat in flood water for over 12 hours in 1966. It took decades before conservators could return it to view.

See the numbers

A large old painted wooden panel lying on padded supports in a conservation studio, partly covered with protective tissue paper — AI-generated image, not a photograph of a real person or place.

FOUR RULES CONSERVATORS WORK BY

Every touch-up
should be undoable.

These come from the National Gallery's glossary and the American Institute for Conservation's guidance on inpainting. They describe professional practice, not a home repair method.

Stay inside the loss
New paint goes only where original paint is missing, never over it, and is not used to strengthen a weak signature.
Use a different, soluble paint
Retouchings are made in a soluble medium that differs from the original, so a later conservator can remove them.
Keep it detectable
Repairs should show up under common examination methods such as microscopes, ultraviolet light and raking light.
Photograph and record
Document where the inpainting is and how it was done. Photographs taken before treatment are especially important.

ONE PAINTING, TWO NUMBERS

Some repairs
take a lifetime.

Giorgio Vasari's Last Supper (1546),
damaged in the Florence flood of 1966.

12+ hours

Time in water, mud and heating oil

During the flood of 4 November 1966, the painting was submerged for over 12 hours, which softened the paint and saturated its wooden panels.

SUBMERGED · GETTY

50 years

Years before it went back on display

Hidden for 50 years to the day, it returned to the Museum of the Opera of Santa Croce in 2016 after a decade-long project by the Opificio delle Pietre Dure.

OUT OF VIEW · GETTY

Getty says the painting, over 8 by 21 feet on five panels, has been through no fewer than seven major floods in its 470-year life. A button now winches it up towards the ceiling if flood water threatens.

HOW MUCH TOUCHING UP?

From a few dots
to a full match.

Conservators and owners agree how far a repair should go. Pick an approach to see what it involves. The bar shows how much new paint goes onto the object.

Describes professional museum practice. Valuable works are treated by trained conservators, case by case.

Touch-up check

Choose an approachHide it with the mountA few dots of colourTone to the backgroundTratteggio linesMatched retouching

Hide it with the mountNo new paint

For works on paper, the AIC notes that areas covered by a window mat may not need inpainting at all.

A few dots of colourRestraint

On original paper, one or two dots of colour may be all that is needed to restore the continuity of a design, the AIC guidance says.

Tone to the backgroundGeneral toning

The loss is toned to sit quietly with its surroundings rather than rebuilding missing detail: sympathetic, but detectable.

Tratteggio linesVisible up close

Fine lines of colour fill the loss. From a distance the image reads as whole; with scrutiny the modern work can be told from the original paint.

Matched retouchingInvisible to the eye

The National Gallery says retouching is usually meant to be invisible to the naked eye, but is done in a soluble medium that differs from the original.

Sources: American Institute for Conservation (AIC) Wiki, BPG Inpainting and Inpainting lexicon entry; National Gallery, London, glossary: Retouching.

A close-up of a filled loss in an old painting, retouched with fine parallel hatched lines of colour — AI-generated image, not a photograph of a real person or place.

INVISIBLE OR HONEST?

Stop where
guesswork starts.

For centuries restorers tried to make repairs disappear. From the 1950s attitudes changed, and methods like tratteggio and selezione cromatica let viewers tell modern repair from original paint. The theorist Cesare Brandi put the limit simply: reconstruction should stop when hypothesis begins.

Nothing on the surface is meant to be forever. The National Gallery notes that varnishes darken and discolour over time and need removing and replacing, and that retouchings are made in a soluble medium so they can be removed easily.

In conversation

Questions people ask

Is retouching the same as inpainting?

They are often used interchangeably. The AIC lexicon says inpainting is new paint added only into areas of loss, while overpainting partly or completely covers original paint, which conservators avoid.

Why not use the same paint as the artist?

So the repair can be removed later. The National Gallery says retouchings are done in a soluble medium that differs from the original. The AIC adds that different pigments can make repairs easier to detect.

Can you see the repairs in a museum?

Usually not with the naked eye, unless a visible method such as tratteggio was chosen. Repairs should be detectable with microscopes, ultraviolet light or raking light.

Why do repairs look different under some lights?

This is metamerism: two colours that match under one light can differ under another, often because the paints contain different pigments. Conservators try to match under the lighting the work will be seen in.

Who decides how much to retouch?

The AIC says the decision is made with the curator, owner or custodian, who should be told the limits and possible consequences. The extent of inpainting is agreed case by case.

Sources

Each figure on this page comes from the sources below.

Only where
it's missing.