Fra Bartolomeo's The Rest on the Flight to Egypt with John the Baptist (circa 1509) hangs among the many masterpieces that adorn the walls of the J. Paul Getty Museum. Visitors to the Museum need no historical knowledge to appreciate the beauty of this painting. Anyone can enjoy the Baptist's playful gesture, the Christ-child's expressive glance and Bartolomeo's skillful rendering of the Holy Family fleeing Bethlehem. Five hundred years of accumulated varnish, grime and dust have dimmed the brilliance of this Renaissance masterpiece.

Over the centuries, restorers applied varnish to the painting to protect and brighten its surface. Each application of resin deteriorated over time turning it darker than before.

The restoration plan calls for conservators to examine Bartolomeo's masterpiece using a variety of 20th century tools. Then, following exact procedures, they apply the gentlest, most effective solvent to the varnish and swab the resin away.

The Rest on the Flight to Egypt with John the Baptist, Fra Bartolomeo, Italian, 1472-1517.

The conservator scrapes a surgeon's scalpel along a hair-line crack to remove a speck of varnish and paint from the canvas.

His oath resembles the physician's: First, do no harm.

"I try to bring a damaged work of art to as close to its original condition as possible," says Andrea Rothe, a conservator at the Getty Museum. "It is critical that everything I do is reversible. I must allow the creative and emotional aspects of the work to speak to an audience without suffocating them with my own interpretation."

From a 50 microgram sample, Michael Schilling, a chemist at the Conservation Institute, determines the chemical composition of the varnish and underlying paint. "The solvent that the conservator uses to strip the varnish from the painting must not dissolve the material that binds the pigment," he explains.

Michael injects the prepared sample into an HP 6890 Gas Chromatograph that combines with an HP 5972 Mass Spectrometer and an HP 9000 workstation to analyze the unknowns. The gas chromatograph processes the sample, separating compounds of the varnish and the paint based on their physical and chemical properties. The mass spectrometer bombards the separated compounds with an electron beam, causing them to fracture into unique patterns. The HP 9000 then matches each pattern to one of thousands of patterns for known organic compounds stored in computer memory.

Michael Schilling uses a probe to insert a sample directly into the HP 5988A Mass Spectrometer to identify organic material contained in varnish and paint.

Michael reviews the chromatogram to determine which organic material (protein, oil, wax, resin or plant gum) binds the pigment and which resin makes up the varnish. He reports the results to the conservator.

The HP GC/MS identifies organic materials contained in the paint and the varnish so that the conservator can select a solvent, enzyme, emulsion or gel to remove the protective coating without damaging the paint.

The conservator moistens a natural sponge with distilled water and gently wipes the painting. With a natural-bristle brush, he applies the cleaning solution. The gel is applied and remains on the painting for nearly three minutes. Then the gel -- together with the varnish -- is wiped away.