For a whole month each year, from 5:30 to midnight, when all the tourists are gone, a team from the Vatican comes into the Sistine Chapel to clean it, check for damage and report on the health of some of the world's most treasured art.
It's a painstaking process: scaffolding must be erected and taken down each night but can't lean on the walls to avoid damaging the paintings.
"We check if there is flaking of the paint layer," Francesca Persegati, the Vaticans Museum's Chief Restorer for paintings told CNN. "We also knock on the plaster to see if it is detached from the masonry."
Salt & paper
One of the biggest problems of the Sistine Chapel is humidity, according to Persegati. It's mostly caused by the flow of 25,000 visitors a day.
"Our bodies are made of water so when we visit the Sistine Chapel, we bring in humidity and heat, everyone heats the environment like an 80-watt bulb," said Persegati.
Humidity causes condensation and a veil of salt forms on the famous frescoes painted in the 15th and 16th centuries, which damages the color and the plaster it's painted on.
To remove the salt layer a laborious technique involving distilled water and thin Japanese paper is required.
"We take plain, distilled water without any salt and with a brush apply a very thin layer on the surface," said Persegati. "Salt is soluble so we wrap it into the paper and removing the paper, we remove the salt."
An array of 30 hidden sensors is in place around the Sistine Chapel to measure temperature, air circulation and the number of visitors. High tech air purifiers were installed in 2014.
The temperature of the hall must remain between 22 and 24 degrees Celsius and humidity between 55 and 60 percent, according to Vittoria Cimino, Chief Conservationist at the Vatican Museums.
"They are very precise markers and we have to verify that the system respects them, said Cimino. "For now, we are very satisfied with it."
Today, modern technology and lighting not only allow for better cleaning but have revealed to restorers the true colors Michelangelo painted in.
The world was shocked after a cleaning and restoration in the 1990s to discover that Michelangelo actually used vivid greens, purples and reds because for centuries it was assumed that he painted in dark, subdued tones. But that was only the accumulation of dirt and grime.
"It was an enormous gift to be the first generation after 500 years to have the privilege of seeing the colors used by the Maestro Michelangelo," said Cimino.
The next time you're in the Sistine Chapel, look out for little black marks, squares and triangles on some of the paintings. They're called witnesses, deliberately left as evidence for future restorers to give an idea of just how dark the paintings were before.
To make sure the colors stay vibrant, a color team measures any changes to tone by taking pictures of the frescoes with a multi-wavelength camera which is then analyzed by a computer.
"We can see the color of every single pixel and compare it throughout the years," said Fabio Morresi, who is in charge of color analysis for the Vatican Museums.
"In six months we'll measure again and see if something has changed. It's important because we can detect any changes even before they are visible to the human eye."
With some 6 million pairs of eyes gazing at these paintings each year, it's a behind-the-scenes labor of love to keep the past shining bright for the future.
- Vatican's Sistine Chapel gets annual check-up
- Breastfeeding in Sistine Chapel OK with Pope Francis
- Vatican Fast Facts
- Vatican removes archbishop, but doesn't say why
- Vatican responds to PA abuse report
- Pennsylvania AG: Vatican knew of cover-up
- Vatican: Catholic bishops to return to China
- Godspeed! Vatican launches official athletics team