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The ideal location will be as dust-free as possible. You should also consider spraying down the floor and/or walls to reduce the chance of stirring up dust. Good ventilation is a must. It helps remove dust and other contaminants and also removes the excess paint and thinner from the room. This will protect yourself from toxic materials in the paint, as well as protect your paint job from anything falling off of your body. Having your head and body covered minimizes the risk of a hair or piece of lint falling onto the paint surface. At the very least, a mask/respirator is a must for safety. Paints and paint thinners (also known as reducers) contain volatile organic compounds (VOCs). These VOCs are flammable and toxic. They are dangerous to inhale and are also absorbed through the skin and eyes. The tape should outline the part of the rim you wish to paint without touching it. The part of the wheel that you want to paint should not have any tape on it. This can be a slow and tedious process depending on the design of your wheel and whether or not you opted to remove your tires and valve stem. This will be the primary protection from overspray. By blocking the excess paint from landing on other surfaces of the wheel, you save yourself a lot of time trying to clean it off later. Any overspray that does end up in unwanted places will have to be carefully removed with lubricant and a clay bar. Trim out the center of the plastic. This will expose the section of the wheel you wish to paint. Tape the outside of the circle you made (the cut edges of the plastic) and down to the first layer of tape that you laid. Tape the rest of the plastic edges down as well. This will seal off any entrance for overspray to get on the rest of your wheel.

Summary:
Choose a place to paint. Wear protective gear. Put tape around the perimeter of your paint surface. Cover the entire wheel in plastic or paper wrap. Cut the plastic with a razor.