This week, 133 cardinals have gathered within the Vatican to elect a latest leader of the Catholic Church. During their deliberations, the one indications of their progress are the regular plumes of smoke wafting from a freshly installed chimney perched on the roof of the Sistine Chapel.
Tradition holds that black smoke indicates the cardinals haven’t yet agreed on a latest leader, while white smoke signals that a latest Pope has been elected.
But what type of smoke is it exactly? Let’s take a have a look at the science.
The tradition of cardinals burning their ballot papers to take care of secrecy dates back to a minimum of the fifteenth century. However, it wasn’t until the 18th century – when a chimney was installed within the Sistine Chapel to guard Michelangelo’s frescoes from soot – that the resulting smoke became visible to anyone outside the chapel.
At the time, the smoke was not intended as a public signal, but once it was visible, onlookers began interpreting it as an indicator of the voting consequence.
By the nineteenth century, it had turn out to be customary to make use of smoke deliberately: if smoke was seen, it meant no Pope had been elected, whereas no smoke indicated a successful election. This in fact lacked clarity and sometimes caused confusion.
The Vatican eventually sought to make clear matters by formalising the practice of fumata nera (black smoke) and fumata bianca (white smoke). Initially, damp straw and tar were added to the burning ballots. As anyone who has tried to light a humid bonfire knows, wet oily fuel will be difficult to ignite, but once it gets going, it produces loads of dark smoke.
This is the results of incomplete combustion: the energy from the flames is initially used to evaporate the water, which keeps the hearth’s temperature low. As a result, lots of the larger molecules within the tar don’t fully combust, resulting in the production of soot and dark smoke.
However, once the moisture is driven off, the hearth burns more efficiently, producing mainly steam and carbon dioxide. At that stage, the smoke diminishes and becomes much lighter.
This fluctuating fumata – combined with the subjective interpretation of its color – caused considerable confusion, particularly throughout the 1939 and 1958 conclaves. It wasn’t clear whether grey smoke was closer to black or white, for instance.
By the Seventies, the straw method had been abandoned in favour of more controllable chemical mixtures. This has since evolved into an unambiguous method for generating the required smoke signals.
Current recipe
In 2013, the Vatican confirmed that their fumata recipes now consist of a transparent black smoke recipe: potassium perchlorate (KClO₄), an “oxidising substance” that gives oxygen to the response; anthracene, a hydrocarbon derived from coal tar that serves as a heavy smoke-producing fuel; and sulphur, added to regulate the burn rate and temperature.
The result’s a deliberately inefficient combustion response, producing a high volume of unburnt carbon particles. This abundance of carbon (soot) makes the smoke thick and black – akin to the smoke you would possibly see from burning oil or rubber, which is wealthy in carbon-based particles.
Meanwhile, white smoke is produced using a much cleaner fuel mix and a more powerful oxidiser. Potassium chlorate (KClO₃) – much more reactive than perchlorate – ensures a hot, vigorous burn. Lactose acts because the fuel, burning quickly and cleanly into water vapour and carbon dioxide.
The rapid combustion of sugar yields large amounts of gaseous output (steam and CO₂), generating a voluminous white cloud. The final ingredient, pine rosin, produces thick white smoke when heated – releasing tiny droplets and light-coloured ash that appear whitish. It also accommodates terpenes that burn to yield a pale, visible smoke.
When combined, the oxidising power of potassium chlorate allows the lactose and rosin to burn hot and fast, yielding mostly clean combustion products together with a cloud of vapour and resin particles.
Rather than soot, the smoke accommodates microscopic droplets and positive solids which can be transparent or white. The result’s a combination of steam and white or light gray smoke that contrasts sharply with the dark, carbon-rich black smoke.
Over the years, the papal conclave smoke signal has evolved from an incidental byproduct of burning ballots right into a fastidiously engineered communication tool.
Today, because of modern chemistry, the smoke is unmistakable – thick black billows for inconclusive votes, or a brilliant white plume when a latest pope is elected.
Mark Lorch is a Professor of Science Communication and Chemistry, University of Hull
This article was originally published by The Conversation and is republished under a Creative Commons licence. Read the original article
