When the Catholic Church elects a new pope, the world is not about watching in a press conference or social media post, but about smoke on a small chimney above the Sistine Church.

If the smoke is black, no new pope is chosen. If it is white, a decision has been made: We have a Pope - We have a pope. It was highly dramatic, live broadcasts for millions.

But what the audience doesn’t see is the hidden complexity of the centuries-old ritual: elaborately built chimneys, engineered stoves and precise chemical recipes, each section is carefully designed to ensure smoke smoke.

Experts told the BBC that the process requires "two custom fireworks", smoke testing rehearsals and Vatican firefighters backup. It is carefully organized by a team of engineers and church officials who work together.

Pope Francis died on Easter Monday at 88 and as the funeral ended, attention turned to the meeting - a private meeting will choose the new pope.

The Vatican has confirmed that the Cardinal will hold a meeting at St. Peter's Basilica on May 7 to celebrate a special mass before gathering inside the Sistine Church, where the complex will begin.

The tradition of burning cardinal’s paper voting dates back to the 15th century and became part of a ceremony designed to ensure transparency and prevent tampering, especially after the delays in the earlier papal elections led to public frustration and unrest.

Over time, the Vatican began to use smoke as a way to communicate with the outside world while retaining strict voting confidentiality.

Today, despite countless progress in communication, the Vatican has chosen to maintain tradition.

"From ancient times, people have seen smoke sacrifice in the Bible's animals and grains, or the traditionally burning fragrance - as a form of communication with God's humanity," Candida Moss, a professor of theology at the University of Birmingham, told the BBC.

"In the Catholic tradition, praying' to God. The use of smoke evokes these religious rituals and the magical and mysterious aesthetic that accompany them."

Professor Moss also said that the rising smoke caused people to gather in St. Peter's Square "included-as if they were included in this mysterious and secret event".

The reason is symbolic, but making it work in the 21st century requires realistic engineering.

In the Sistine Church, two furnaces were temporarily installed, specifically for conference-style installations: one for burning ballots and the other for generating smoke signals.

Both furnaces are connected to a small smoke channel - A pipe inside the chimney that emits smoke - leading up from the roof of the church to the outside. Firefighters were seen on the roof carefully secured the chimney tops in place on Friday, while workers erected scaffolding and built stoves inside.

Built 500 years ago, Sistine Chapel is home to one of the most famous ceilings in the world. It is decorated with Michelangelo's frescoes, it was not designed for smoke signals and requires careful and safe installation of chimneys.

This is a complicated process. The technician either uses existing openings or creates temporary hatches that insert a flue that is usually made of metal, such as metal or steel. The pipes run from the stove to the outside and through the tiled roof above St. Peter's Square.

Each joint is sealed to prevent leakage and each component is tested. Experts perform smoke tests a few days before the meeting begins to ensure the chimney draw works in real time. Even Vatican firefighters were involved. If a failure occurs, please standby.

"It's such an exact process because if one thing goes wrong, it's not just a technical failure - it's an international event," Kevin Farlam, a structural engineer who worked at Heritage Properties, told the BBC. "It's not like putting pipes on a pizza oven. Every part of the system has to be installed without damaging anything."

This setup was built a few days before the Cardinal arrived, once the Pope was chosen.

To ensure visible signals, Vatican technicians used combinations of compounds.

Professor Mark Lorch, head of the Department of Chemistry and Biochemistry at Hull University, told the BBC that he said: “They are essentially two custom fireworks built here.”

"For black smoke, a mixture of potassium perchlorate, anthracene and sulfur is burned - producing thick deep smoke.

“For white smoke, a combination of potassium chlorate, lactose and rosin protein was used, burning clean and pale.

“In the past, they tried to burn wet straw to create deeper smoke and dry straw to make the smoke lighter – but that caused some confusion because sometimes it looked grey.”

He explained that the chemicals were "pre-packaged into the cartridge and ignited electronically" so there was no ambiguity.

The addition of the Bell ringtone introduced during the elections of Pope Benedict XVI - is now confirmed and used with the smoke signal.

Over the years, there have been suggestions for modernizing the system: colored lights, digital alerts and even television votes. But for the Vatican, rituals are not only a tool of communication—a continuous moment of tradition for centuries.

"It's about tradition and secrecy, but it also has real theological significance," Professor Moss said.

“Plus 'Catholic Church' and 'cutting' are far from synonyms – innovation is almost the opposite of ritual.”