Burning Test

If you work with textiles, it is necessary to learn and identify the different types of fibers. But how should you do this? Memorize a book listing every kind of fiber with its property? The answer is obviously no. There is a famous saying by John Dewey:“You learn what you do.”As a strong believer of this doctrine, I recommend you experiment with burning test. You should burn few types of fibers and see how they differ.

When something burns, it is reacting with oxygen. This is called oxidation reaction. Rust on iron is a slow type of oxidation reaction. Breathing is also a form of oxidation reaction. Water and carbohydrates are formed as by- products of glucose burned with oxygen.

Because different types of fiber are made with different substances, each burns with distinctive smell, flame, and ash. It is not necessary to know the burning properties of all existing fiber types. Let’s just take a look at few major ones.

Cotton, the most common type of fiber, is mostly composed of cellulose made from carbon, hydrogen, and oxygen. Cellulose is a substance found in plants. So cotton burns like paper in small and easy flames. It gives off the smell of burning paper and leaves a white ash. If burned slowly, cotton turns into charcoal as the wick in an oil lamp does.

Burning test shows whether the fabric is 100% cotton or blended with other fibers. Warp and weft yarns of the fabric are tested separately. If both burn like paper, the fabric is 100% cotton. A yarn is polyester if it burns quickly with black smoke and forms dark round drops. Synthetic fibers produce black smoke because they are made of polymer compounds with more amount of carbon. Carbon requires a huge amount of oxygen to be burned completely. Due to the lack of oxygen in air, carbon molecules are blown off as black smoke.

Rayon, a type of cellulose fiber, burns like cotton. So it is difficult to identify rayon by burning test. Instead, drapery of fabric is checked. Another way is to look carefully at the fiber, which is longer and glossier than cotton fiber. Rayon-cotton blended fabric, however, is easily distinguished by burning test. Instead of burning in flames and leaving a white ash, it melts and produces grey colored ash. Hemp is another type of cellulose fiber that burns just like cotton. It is impossible to differentiate linen, ramie, and other types of hemp fibers by burning test. Acetate and triacetate are also composed of cellulose but they are distinctive since they burn with black smoke and sour smell.

Wool is also easily identify by burning test. It is made of keratin, the protein found in human hair. In fire, it slowly curls up and produces sulfur smell. The pungent smell makes it easy to identify. Silk also gives off a similar smell when burned. Wool is often blended with acrylic, synthetic fiber that melts in fire. There is a major difference between wool and acrylic when they turn into ash: wool ash crumbles easily whereas acrylic ash remains hard.

Besides acrylic, there are many other types of synthetic fiber like PVC, PU, and PE that show subtle differences in burning test. I stop here because I am not trying to make a textile scientist out of you. What is said above should be enough to get you through your daily work with textiles.