VATICAN CITY — Workers from the Vatican's Mosaic Workshop are restoring mosaics at the highest reaches of the Cupola Clementina inside St. Peter's Basilica in Vatican City. The dome rises 200 feet above the pews of the basilica, and only restoration workers can access its uppermost sections during the project.

The work is overseen by Paolo di Buono, director of the Vatican's mosaic workshop. Most of the artworks inside the basilica are mosaics rather than paintings. Made of glass and gold, mosaics are more durable than paintings, which are susceptible to deterioration over time.

Up close, the mosaics consist of broken fragments that form recognizable images only when assembled together. From a distance, they appear similar to an Impressionist painting — an effect achieved through color work by generations of artisans. One method employed in the workshop is the filament technique, which involves warming and firing glass colors to melt them and create new colors.

"Using different kind of colors and melting the tiles in this way, they were able to reach many kinds of shades of colors in a very fine way," di Buono said.

The tools and techniques used in the workshop have remained largely unchanged for centuries. The platforms used by mosaic workers are identical to platforms once used in ancient Rome 2,000 years ago. Workers use a sharp hammer called a martellina to cut mosaic pieces into tiny fragments, a practice that has persisted across millennia of the craft.

"It is very incredible that they, the mosaicists, used this kind of detail to represent, for example, this beautiful face," di Buono said of the artistry visible in the cupola's mosaics. "Absolutely. It is not possible to be used to working here because you are always amazed."

Archive records trace the history of the basilica's mosaics back centuries. The earliest records of St. Peter's mosaics date to 1580. Among those documents is a blueprint for a mosaic of St. Peter that specifies a gradient of turquoise color to be used in the composition. The archive of St. Peter's, which conserves the earliest records of the Vatican's artworks and of the basilica itself, is housed inside a smaller dome of the church. Simona Turriziani leads the archive.