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A wide variety of commercial cleaning products can help you clean brass.  While the specific directions for these products vary with manufacturer, generally you will spray the product on the brass hinge, then wipe it down with a clean cloth.  Popular brass cleaning products include Wright’s Premium Brass Cleaning Polish and Brasso Multipurpose Polish. Test the cleaning product on an inconspicuous area of the hinge before applying it to the whole thing.  If the cleaning product causes the brass plate to flake off, discontinue use of that product and try another instead. Consult manufacturer directions before using any brass cleaning product. Apply a thin patina of ketchup, marinara sauce, or tomato paste to the brass hinge using a paper towel or hand cloth.  Allow the tomato-based product to remain on the brass hinge for about 60 minutes.  Dip a clean cloth or sponge in hot, soapy water, then scrub the brass hinge. This technique also works with Worcestershire sauce and hot sauce. Combine equal parts vinegar, salt, and flour.  For instance, you might combine two tablespoons of vinegar, two tablespoons of salt, and two tablespoons of flour.  Smear this paste across the surface of the brass hinge.  Wait for about 60 minutes.  Rinse the hinge off with warm water.  Wipe it down with a dry cloth until it shines. Cut a lemon in half and remove the seeds from one half.  Cover the half of the lemon you removed the seeds from with salt.  Rub the face of the lemon (the flat side covered in salt) over the brass hinge.  As you rub the hinge, add additional coats of salt to the lemon as it flakes off. Wipe the hinge down with a clean cloth. Combine two tablespoons of cream of tartar and one tablespoon of lemon juice.  Rub the paste on the hinge using a clean paper towel or an old toothbrush.  Allow the paste to sit for 30 minutes.  Then, dip a clean cloth in warm water and wipe the paste away. Mix equal parts white vinegar and baking soda in a bowl with steep sides.  For example, you could combine two tablespoons vinegar and two tablespoons baking soda.  The ingredients will fizz when combined.  Dip a soft-bristled brush or a soft cloth in the mix and wipe down the brass hinge for a minute or two.  Wipe the hinge clean with a damp rag, then dry it with a clean dish cloth. Use a spatula to lightly cover the hinge in plain yogurt.  Try to stand the hinges on their edges so as to coat the maximum surface area possible with yogurt.  Allow the yogurt to dry overnight.  Rinse the hinges thoroughly using warm water.  Use a toothbrush to get the yogurt out of any recesses where it might have coalesced. Another dairy-based cleaning solution involves combing equal parts water and milk.  For instance, you might mix five tablespoons of water and five tablespoons of milk in small pot.  Whatever volume of each you choose to combine, ensure it coats the hinges completely.  Place the hinges in the pot, bring it to a boil, then turn the heat to its lowest setting.  The amount of time it takes to get your brass hinges clean by simmering them in milk depends on the extent of grime and tarnish the hinges have acquired.  Use tongs to pull the hinges out every 10 minutes  and examine them. If they’re clean, turn the stovetop off and rinse your hinges in water. If the hinges are not clean, drop them back in their milk bath. Place your brass hinges in a crockpot.  Cover the hinges with water.  Set the crockpot to low and let the hinges “cook” for a few hours.  Pull the hinges out using tongs or just conduct a visual inspection to discern whether the paint is coming off.  If the paint is coming off, remove it and restore the hinge to its rightful place. If it is not, place it back in the crockpot for another few hours. If, after another dip in the crockpot, the paint is still not coming off or has only partially come off, rub a cloth dampened with mineral spirits over the entire surface of the hinge.  This should further loosen the paint. This technique also works for removing lacquer from brass hinges.

Summary:
Use a commercial cleaning product. Smear a tomato-based product on the hinge. Make a vinegar paste. Clean the hinge with a lemon. Create a paste from cream of tartar. Combine baking soda and vinegar. Coat the hinges in yogurt. Simmer the hinges in milk. Remove paint from your hinges with a crockpot.