Protective masks are used to prevent the spread of the virus rather than protecting people from the virus. One of the common ways of transmission of the coronavirus is air. Infected into the air by methods such as sneezing, coughing and exhaling, the virus can easily be transmitted to other people. The use of masks prevents the virus from spreading this way. The company LaVision has created a video that shows how protective masks work. In the video published on LaVision’s YouTube channel, Schlieren, a 150-year-old photography technique, is used to visualize the air flow caused by the exchange and cough of a person. In the published video, the air flow created by a person using a mask and a person using a mask is seen. The video clearly shows how the use of the mask prevents the spread of the virus. 150 years of photography technique: Schlieren Background Focused Schlieren method was used in the preparation of the video, which shows how protective masks work. In the statement made by LaVision regarding the technique used, “Schlieren method is a simpler and more cost-effective alternative to laser imaging methods. Because a complex lighting device such as laser is not needed ”. The Schlieren photographic technique was invented in 1864 by the German physicist August Toepler to study the supersonic movement. The Schlieren technique has been used by aviation engineers to photograph the flow of air around objects. Long video showing how protective masks prevent the spread of viruses