VATICAN CITY: A small workshop in the Vatican, which has existed since the late 1500s, has been working hard to preserve the mosaics that adorn the colorful interior of St. Peter's Basilica.

The 12 artists who work at the Vatican Mosaic Studio also create smaller artworks that Pope Leo gives as gifts to foreign leaders. He presents these mosaics to visiting officials at the Vatican or during his trips abroad. This tradition is sometimes called "mosaic diplomacy."

It can take several months to complete just one mosaic. The artists carefully place thousands of tiny colored tiles together to create religious images, such as Jesus or Mary, or non-religious scenes like Rome's Colosseum.

Paolo Di Buono, the studio's director, said it is important to continue using mosaic techniques because they help preserve an ancient tradition. He explained that their work is meant to last for centuries and that they feel they are creating something almost eternal.

Inside St. Peter's Basilica, the studio takes care of 8,360 square meters (about 90,000 square feet) of mosaics, including those in the main dome. Mosaics were chosen instead of paintings because candle smoke and incense during church services could damage paintings.

One of the studio's recent works is a portrait of Pope Leo, placed in Rome's Basilica of St. Paul Outside the Walls. Three artists worked on it for five months, using around 16,000 small tiles.

Artist Nicoletta Marino said the work requires great care and patience because the tiles are so small.

Another artist, Adriano Galise, showed photos of mosaics he made that were given by Pope Benedict XVI to U.S. Presidents George W. Bush and Barack Obama during official Vatican visits.

Di Buono said giving mosaics as papal gifts is one of the Vatican's most important traditions.

Each artist has a different way of working. Galise begins with a black-and-white image and plans where each tile will go, like a puzzle. Others prefer to start with a colored picture or drawing.

The studio is not only a workshop but also a historic archive. It keeps 27,000 types of colored tiles in a large cabinet with 9,000 drawers spread over two floors.

About 23,000 of these tiles are very old and cannot be produced anymore. Some were made with poisonous materials that are no longer used. These rare tiles will eventually run out.

For the portrait of Pope Leo, the artists used some of these old tiles to show the shading on his face better.

In St. Peter's Basilica, the studio's artists are also restoring mosaics in the dome of the Clementine Chapel, one of the church's oldest and most respected areas. It is located in the grotto near the tomb of St. Peter, the first pope.

Di Buono said the studio's role is to protect and preserve the works of earlier artists. He said they see themselves as part of a long chain, continuing the work of those who came before them.