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Calipers are exposed to very high temperatures during braking. Choose a paint that is heat resistant or developed specifically for calipers.  Specialty caliper paints can be purchased from auto parts stores. Purchase a heat tolerant spray paint from your local hardware store. Make sure the paint is designed for use on metals. Spray multiple coats to achieve an even paint job. Do not apply spray paint in thick coats or you will get drips and runs in your paint. Spray smoothly and from different angles to get maximum coverage.  Shake the can and follow the label directions on the paint can. Spray short bursts, not a continuous stream of paint. Move the can from side to side as you spray. Wait 5 minutes between coats of paint. Spray 3 to 4 coats on the top side of the caliper. After applying multiple coats to one side of the caliper, wait for it to dry to the touch before turning it over.  Repeat the painting process on the opposite side of the caliper Be gentle when turning the caliper so you don’t twist the brake line. You do not need to paint the inner portion of the caliper as this isn’t seen and may affect the performance of your brakes. Depending on the temperature and humidity, the time it takes for your paint to dry may vary. You don’t want to ruin all your hard work, so make sure the paint is completely dry before replacing the caliper.
Select a high quality paint. Paint the caliper one side at a time. Allow the caliper to dry for 30 minutes, then paint the other side. Allow the paint to dry for one hour before replacing the caliper.