Clean the leather surface, and remove any oil or leather protectants with a grease remover. Mount the leather on a board. If necessary, use spring clamps to stretch the material, so the work surface is flat and smooth with as few wrinkles as possible.
Set up a work space with a spray booth in a well- ventilated area. Connect the airbrush to the air source, and put on a face mask.
If you have a prepared design, use a projector to transfer the image to the surface. Sketch the design in pencil. When working on black leather, use a white pencil. Alternatively, you can paint a light, misty, white base coat and when the paint is dry, sketch the design with a graphite pencil. Apply any masking required by the design.
Select a color of textile paint, and load it into the airbrush paint cup. Start filling in the design with paint. Change colors, and adjust the masking as necessary to finish the picture.
When the painting is done and thoroughly dry, heat-set the design. You can use a heat press, a hot air gun for five minutes at high heat or a clothes iron with a protective cloth for 30 minutes at medium heat.