There are various reasons why people paint home door locks made of metal. The reality is that paint helps to protect these devices from damage while giving them a more refined look. That is why it makes great sense to use it. Here is how to do this correctly.
Get primer and paint which are especially formulated for the type of metal that the door lockset is made of - It is equally important for the paint to provide protection from rust, corrosion and scratching to the metal. It is up to you to decide whether to go for spray or liquid products. The former are easier to apply while the latter allow for greater precision. If you choose liquid primer and paint, get appropriate soft brushes as well.
Clean the locking device thoroughly and dry it - Dissolve a few drops of liquid detergent into a bowl of water and dampen microfiber cloth. Rub all surface gently. Rinse the hardware with another piece of cloth dampened in fresh water. Use a third piece for drying. Remove rust with a paste from equal portions of lemon juice and vinegar and a sufficient amount of baking soda. Do not use abrasive tools, as this may pose the need for lock repair or even replacement.
Add painter's tape around the lockset - After you do this, cut a small piece of the tape and make a roll corresponding to the size of the keyhole. Insert the piece into the keyhole to protect it. Do not push it too far. Otherwise, you may end up needing repair similar to broken key extraction.
Apply the primer carefully - If you use spray product apply it from all sides. Remember to keep the nozzle as close to the surface as possible. If you use a brush, you must remember to cover the edges right next to the surface of the door. Let the primer dry for as long as necessary.
Paint the metal surface - Apply a thin layer of the paint only. Do not rush things. If you use a brush, you should follow one and the same direction when making strokes to achieve uniformity. Look at the lockset from all sides to confirm that the entire surface is covered. Let the paint dry fully before you use the locking device again.
You can use the same strategy for painting both external and internal door locks.