Conservation and Restoration of Paintings (Business of Art, 4)

Almost 20 years ago, I wrote a couple dozen essays on the history of painting for, a subscription service that provided online supplementary materials for high-school students. The site’s owners have given me permission to publish the essays (copyright © 2001 Beyond Books) on my website. This essay (lightly edited) is the fourth of five in the section on the business of art. Click “Business of Art” in the Obsessions cloud at lower right to see all that have been published.


Paintings are fragile. Canvas tears. Wood disintegrates. Paint fades and chips. Varnish discolors and gathers dirt. Stretchers and frames warp. In today’s museums, paintings are preserved in nearly ideal conditions, with controlled humidity, filtered light, strictly regulated temperature, and human guardians to make sure no unauthorized hands touch them.

But what does one do for paintings that haven’t been so lucky?


The most important rule for a good restorer is the same as that for a physician: First, do no harm. The first step in today’s conservation process is a detailed study of the painting, to record its present state and work out a solution for the damage.

This stage may include x-rays and infrared or ultraviolet photography, which show previous repairs and details buried under layers of paint and varnish. Sometimes restorers take a microscopic sample from an inconspicuous part of the painting in order to determine the chemical content of the original paint and varnish, so that they can prepare cleaning solutions that will not further damage the work.

Cleaning the Sistine ceiling

All these processes and more were performed before restoration began in the 1980s of the Sistine ceiling frescoes, which were painted by Michelangelo from 1508 to 1512. The frescoes had been obscured with centuries of candle smoke. Water and minerals had oozed through the ceiling, cracking and staining the painting. Earlier restorers (1625, 1710, 1935) had applied varnish, glue, and paint. Until the late 20th century, the Sistine Chapel’s only ventilation was via open windows. Outside dust and dirt such as particles from auto exhaust also built up on the fresco.

This is the ceiling as it appeared before the restoration.

Michelangelo, Sistine Chapel ceiling, late 20th century. Image: Wikipedia

To remove 500 years of accumulated dirt, restorers carefully cleaned the ceiling with deionized water. Then they applied a gentle gel with a solvent (for stubborn dirt) plus antibacterial and antifungal agents. That solution was removed with more water. The restoration, completed in 1989, took longer than it took Michelangelo to paint the ceiling.

The restored Sistine ceiling fresco has brilliant colors.

Section of the restored Sistine Chapel ceiling. Image: Jean-Christophe Benoit / Wikipedia
The Prophet Daniel from the Sistine Chapel ceiling, before restoration and after. Image: Wikipedia

To eyes accustomed to the dirty ceiling, the colors were shockingly bright – although no brighter than those in Michelangelo’s Doni Tondo, painted just before the Sistine Chapel ceiling.

Michelangelo, Doni Tondo, 1506-1508. Florence, Uffizi Gallery. Image: Wikipedia

The colors are probably correct, but there may be another problem. The restorers assumed that Michelangelo worked in pure fresco technique, applying color to patches of wet plaster so that the colors became, chemically, part of the plaster. Therefore the restorers removed everything down to the plaster surface, assuming it was a later addition.

But what if it was not? A painter has the option of adding colors to dried plaster, although they’re not as durable as pure fresco. In the cleaned spandrel fresco on the right, some of the details of the painted architecture have certainly been lost, and perhaps also some of the details of the faces.

Two spandrels from the Sistine Chapel ceiling, before (left) and after (right). Image: PDOld / Wikipedia

For more on the controversy over the cleaning of the Sistine ceiling, see this Wikipedia article. And speaking of controversial restorations …

The restoration of the Last Supper

In some cases, even the most expert modern restorers have a horrendously difficult time. Leonardo painted his Last Supper (ca. 1495-97) on a plaster wall. But instead of using fresco, he used a paint of his own invention. The Last Supper began deteriorating within years after Leonardo finished it. Frequent attempts to restore it left many of the figures unrecognizable. By 1975, one observer said the paint looked like scales of snakeskin barely attached to the wall.

Leonardo, Last Supper, 1490s. Convent of Santa Maria delle Grazie, Milan. Image: Wikipedia

Two copies of the Last Supper were made in the 16th century. This one was used by the most recent restorers, along with sketches by Leonardo of the Apostles.

Giampetrino, Last Supper, ca. 1520. Image: Wikipedia
Leonardo, sketches for the Apostles in the Last Supper. Image: Wikipedia

The Last Supper restoration is even more controversial than the Sistine ceiling restoration. One critic said the restored version seemed to have been copied from a color postcard.

Leonardo da Vinci, The Last Supper, ca. 1495-1497. onvent of Santa Maria delle Grazie, Milan. Image: Wikipedia

The non-restoration of the Mona Lisa

And then there are paintings that even the bravest restorers are unlikely ever to touch. Around 1550, half a century after Leonardo da Vinci’s death, Vasari described one of his paintings thus:

The eyes had that lustre and watery sheen which is always seen in real life, and around them were those touches of red and the lashes which cannot be represented without the greatest subtlety . . . The nose, with its beautiful nostrils, rosy and tender, seemed to be alive. The opening of the mouth, united by the red of the lips to the flesh tones of the face, seemed not to be colored but to be living flesh.

He’s describing the Mona Lisa, which apparently had the same vivid colors as Leonardo’s Woman with Ermine. It’s almost certainly yellowed varnish that makes Mona Lisa so dark … but Leonardo was notorious for his experimental paints and varnishes. Who knows what will happen if this varnish is removed?

Leonardo, Mona Lisa, ca. 1503-1517 (Louvre, Paris); and Woman with Ermine, 1489-1490 (National Museum, Krakow). Images: Wikipedia


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