Use an Opaque Projector

• Even for those who are artistically inclined, drawing a mural on a vertical surface can be a challenge. It's difficult to get proportions correct on such a large scale. Therefore, using an opaque projector to trace the image onto the wall is ideal. You can use any sketch, newspaper clipping, magazine picture or photograph. Place it under your projector, adjust the projector so that the image is the appropriate size for your wall and trace the projected image.
  
  

Color Block for Large Areas

• Airbrushing is a time-consuming technique, so it's best to not use your airbrush for every part of your mural. For large objects in your mural, determine the lightest color you'll be using on the object. For example, for a big pumpkin, determine your lightest shade of orange. After you've determined the lightest shade, paint the object with a large old-fashioned paintbrush. After it's dry, airbrush shadows, depth and highlights.
  
  

Use Airbrushing for Highlights and Shadows

• Highlights and shadows add dimension and depth to your mural. Airbrushing is a perfect tool for adding highlights and shadows because the effect is subtle and smooth. To add highlights, airbrush paint in a lighter shade than the object to be highlighted. Make sure you don't add highlights to objects in the background or to objects that shouldn't have a prominent place in the mural. Do add highlights to the most important objects in the foreground. Shadows help give perspective to the mural. Decide where the light is coming from on your mural, and only put shadows on one or two sides of the mural's objects. For example, you may decide to only put shadows on the lower and left side of each object.
  
  

Seal the Mural with Varnish

• Murals that are painted on outdoor surfaces must contend with weather elements. Indoor murals face humidity, chemical cleaners and fingerprint oils. To combat these inevitable hazards, it's important to seal your airbrushed mural with art-quality varnish. For outdoor murals, several coats of wax or polyurethane varnish will make it possible to remove graffiti without damaging the mural. Polymer varnish works well for indoor murals but is not durable enough for outdoor murals.