Flame polishing is the process of creating a smooth surface on a material by melting it slightly with a hot flame. This process is usually used on acrylics and glass to produce a sheen or smooth surface. A torch is necessary to complete this process properly, and the user must have significant skill in the process. When flame polishing is done right, it will produce the smoothest surface possible, much smoother in many cases than other, more abrasive polishing methods. When the heat is applied to the surface, it creates surface tension that stretches the material.
The process of flame polishing is usually used on broad, flat acrylic or glass surfaces, though it can be done to other shapes as well as other materials if the person doing the flame polishing is especially skilled. The torch used to complete the flame polishing process can vary in size, though almost all will burn a combination of hydrogen and oxygen because these chemicals are less likely to contaminate the materials being polished, thereby creating flaws in the finished product. The torch will be connected by hoses to tanks containing these chemicals; the tanks can be regulated to adjust how much of each chemical is burned at any given time.
Unlike buffing, which can create scratches or gouges on the surface of the material, flame polishing prevents abrasive materials from coming in contact with the material at all. It is possible to remove scratches and gouges using the flame polishing technique as well, and in some cases the technique can be used in conjunction with other finishing methods. Flame polishing is also a much quicker process than buffing. Depending on the size of the piece, it may be completely smoothed and polished in only a few minutes, whereas buffing can take hours in some cases.
The torch can be fitted with different tips to control the shape and size of the flame. Some tips are wide and flat, and they are useful for wide, flat surfaces. Other tips are narrower, and they produce a smaller flame useful for edges or crevices. An experienced flame polisher will be able to determine which tip will be most useful for a piece being polished; in some cases, a piece may require the use of more than one tip to accommodate several different surfaces or features.