Test the pressure and adequacy of your airbrush machine. Do this by filling the reservoir of your airbrush machine with a small amount of your base paint. Spray a piece of paper towel. If the paint is too thick and is not passing through the airbrush machine fluently, dilute the paint with a little water. Repeat the test until the paint dispenses evenly.
Coat your canvas with the base color of paint. Flames tend to look better when the base color is very dark. Black is the suggested base color, as it helps to enhance the brightness of the color of the flames. You may need to do more than one layer of the base color to ensure that it covers the entire canvas evenly. The canvas used for this may vary. If the canvas is skin in a body-art aspect, clean the skin with isopropyl alcohol before applying paint. Allow time to dry.
While the base coat is drying, remove the remains of the base color from the airbrush machine. Do this by using a paper towel to clean the reservoir, and then rinse it out with water. Test the cleanliness of the airbrush machine by spraying a paper towel. If it comes out clear, then it is clean. If the paper towel still shows color, then repeat this step until the piece of towel comes out clean. It is imperative that there are no remains of the base color in the reservoir, as it could mix with the lighter colors and ruin the design.
Refill the reservoir with the darkest of the colors used to design the flame, preferably red or blue. Keep in mind that at least three colors will be used for the flame part of the design, so make sure that you thoroughly clean out the airbrush reservoir every time you switch colors. Make sure it is clean and your colors are pure by testing each color on a piece of paper towel.
Lay the flame stencil on the surface of your canvas. Airbrush the flame onto the canvas. Work liberally with the flame stencil so that the design of the flame will look realistic. If you are using blue as a base for the flame design, use it at the bottom of the flame to accentuate its origin. Allow time to dry.
Outline the lines of the flame design with a bright orange paint. You can also use the stencil to enhance the design with the orange paint. Make sure you do not use so much of this color that the ones underneath are no longer visible.
Highlight your flame design with a bright yellow. Go over the lines already created with the stencil. Like the orange color, make sure you do not use too much. The colors must collaborate, not overlap. Allow time to dry, then enjoy your new true flame design!