I am a stickler for details, not show car level but if I’m doing a project I plan ahead. I powder coated some valve covers and noticed the hardware was oxidized and crusty. I am using caswell black oxide and sealer. I also noticed how crazy expensive new hardware is. 1. Clean. I soaked in vinegar for a couple days. Then to a wire wheel on the bench grinder. The better the prep the better the finish. Like any other job. 2. clean again. A dip in a degreaser or other cleaner will do. Dry completely. Compressed air or heat gun will do. 3. Sit in the caswell black oxide in a 1:9 ration with oxide to distilled water. 4. The bolts will turn black before your eyes. Move around and wiggle to release air bubbles. No longer than 5 minutes in the solution. 5. rinse in clean water 6. dip in caswell sealer and let air dry. gloves should be worn at all times. If there are spots that did not take the black coating, it means it was still dirty. Enjoy!