When paper is burned, combustion releases carbon compounds that produce a yellowish flame. The black color that forms on the burnt paper is due to the presence of carbon that remains after combustion.
Paper is essentially made of plant fibers primarily derived from cellulose, a natural substance found in wood. This cellulose consists of long chains of sugar molecules linked together, which makes the paper both flexible and strong. Additionally, there is often some lignin, a natural compound that binds the fibers together but yellows over time. Ordinary paper sometimes contains additives: mineral fillers (like kaolin or calcium carbonate) to make the paper whiter and softer to the touch, as well as glues and inks, in short, small additions based on the final use. Ultimately, when you light a sheet of paper, you are primarily burning long, neatly organized chains of sugar directly sourced from trees.
When you light your paper, it undergoes a combustion reaction, meaning it reacts quickly and strongly with the oxygen present in the air. During this reaction, the long chains of molecules (primarily cellulose) that make up the paper break down due to the intense heat. The atoms from the starting molecules then reorganize, forming new substances, including carbon dioxide, water, black smoke made up of partially burned carbon particles (soot), and various gaseous compounds. This chemical reorganization releases a tremendous amount of energy in the form of heat and ultimately produces the black residue you recognize: carbon that is almost pure, more commonly referred to as charcoal or ash depending on the stage of combustion.
When you burn paper, it is the intense heat of combustion that causes the chemical decomposition of cellulose fibers. As the temperature rises, cellulose breaks down into simpler carbon structures. This notably forms pure carbon, which appears as soot or char, hence the typical black color when paper partially burns. The yellow or brown color observed just before the appearance of black also comes from intermediate degradation compounds, which are often referred to as tars. These residues reflect light differently, resulting in visible variations in hue to the naked eye during combustion. The more complete and hotter the combustion, the purer the carbon will be, which explains why the remaining charred parts usually end up black and brittle once cooled.
When paper burns, several physical phenomena come into play. First, there is a transfer of thermal energy: the heat released rises quickly, carrying hot gases upward, a process known as convection. Then, due to the high heat supply, the particles around become agitated and collide, causing light emission, which is the light and flame we see appearing. This is the same phenomenon that occurs when a piece of metal heated to white becomes luminous. Moreover, this is also how we obtain infrared radiation, which is invisible but very hot. Finally, the reddish-orange color mainly comes from the thermal radiation produced by these incandescent particles at high temperatures. This is why, when observing paper burn, we clearly notice this fascinating play of heat, light, and movement of hot air.
Observing the change in color of paper when it burns provides some nice practical tools. For example, it allows for a quick analysis of the quality of the paper or the presence of certain chemical additives: recycled or treated paper burns differently than a plain, untreated sheet. Some experts even use these burn tones to check the authenticity of old documents, such as manuscripts or paper artworks. Forensic experts rely on this to detect forgeries or counterfeits. An unusual or strange color during combustion can be an indicator that something is not right—such as specific components of the paper, pigments, or specific inks. Lastly, in certain specific cases (like special effects or films), the phenomenon of controlled combustion is exploited to achieve precise shades or particular visual effects directly on paper.
Some special papers, like thermal paper used in receipts, exhibit different chemical reactions during combustion, sometimes producing unusual colors such as green or blue, due to the incorporated chemical additives.
The different shades of yellow, orange, and red observed during combustion come from the incandescence of carbon particles heated to different temperatures.
When the paper burns completely, the black residues observed are essentially pure carbon commonly referred to as 'amorphous carbon' or 'soot'.
By observing the color of a flame, it is possible to roughly estimate the temperature: a typical yellow-orange flame from burning paper indicates a temperature around 1000 °C, while a blue flame indicates a higher temperature (up to 1500 °C or more).
The flames exhibit these warm colors due to the presence of glowing carbon particles. During the incomplete combustion of paper, these suspended particles heat up and emit a characteristic yellow-orange light.
In practice, it is almost impossible to burn paper without producing smoke, as combustion is rarely complete. However, burning at a very high temperature with good air circulation significantly reduces the amount of smoke produced.
This layer is composed of ashes, primarily mineral salts and silicon dioxide found in the paper. These inorganic compounds do not burn, thus forming a slightly colored solid residue after combustion.
Yes, because recycled paper often contains various additives or pigments from the recycling process. This can slightly influence how the paper changes color when burned, resulting in a different hue compared to standard papers.
Sure! Here’s the translation: "Yes, burning paper produces toxic substances, including carbon monoxide, volatile organic compounds (VOCs), and fine particles that can irritate the respiratory tract and have harmful effects on health with prolonged exposure."
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