How to Antique Brass
If you want to make brass look antique, wash the item with soap and water, or use nail polish to remove any lacquer. For a subtle antique look, use a paintbrush to coat the piece with a mixture of equal parts salt and water. Reapply the saltwater daily until you get the result you desire. For more pronounced aging, brush vinegar over the item's surface instead. If you want a greener patina, mix a spoonful of salt into the vinegar first. You could also heat the brass with a hair dryer or in a 450°F oven, but be sure to wear oven mitts when you handle the hot brass.
Make sure the object is brass. Some other metals look similar to brass, but will respond differently to these aging methods. The wrong treatment could corrode your object, so take your object to an antique shop or other expert if you can't identify it yourself. Clean brass has a bright, golden brown appearance. The most similar metals in appearance are copper, which is brown or pink-brown, and bronze, which is a much darker brown. Brass is slightly magnetic, but should only respond noticeably to a powerful magnet. If a small magnet sticks firmly to the surface, you probably have an object made from a different metal, then plated with a thin layer of brass. Learn what to do if your object is not brass. If your object is only brass-plated, try using a gentle treatment such as vinegar or salt water, as harsher materials may corrode through the thin brass layer. If you are trying to age copper, see these linked instructions. To antique bronze, purchase a "bronze ager" and follow the Using Antiquing Solution method. If the brass is lacquered, remove it with nail polish remover. Lacquer is a clear, hard, protective finish that prevents the brass from oxidizing, which is the aging process you're trying to encourage or imitate. Apply the nail polish remover, also known as acetone, to the object to strip off the lacquer. Wear rubber gloves and work in a ventilated area to avoid inhaling fumes. Let small objects soak in the acetone. Use a paintbrush to brush the chemical onto large objects. Be sure to coat every corner of the object. Methyl alcohol, paint remover, or lacquer thinner will also do the job. Pour hot water over the object after treating it with nail polish remover. Wait a few minutes or until the lacquer is peeling off or dissolving into goo. Wash the object in hot water to remove the lacquer Check to make sure there is no remaining lacquer. Modern brass objects are often protected with tough lacquer that can take several attempts to remove entirely. If there is a thin protective film or no finish at all, wash with gentler materials. If the object feels greasy or has a thin layer of polish on it, you can probably clean it with a cloth soaked in rubbing alcohol or a 50/50 mix of vinegar and water. For completely untreated brass, a thorough wash with soap and water should be enough to prepare it for antiquing. Wear gloves even when using these skin-safe cleaning products, since oils from your hand can get on the brass and prevent the antiquing effect from taking place evenly. Dry completely before continuing. Do not begin the antiquing process until the brass is completely dry. A hair dryer, propane torch, or oven can speed up this process. Be cautious when applying heat to a brass object that recently had its lacquer removed. If you missed a piece of lacquer, it could catch on fire or release fumes. Dry the brass in a well-ventilated area with no flammable objects nearby. You can now use any of the methods described below. If you're unsure which to use, read the first step of each one to learn the benefits of each option. Use vinegar or salt water to antique your brass safely and easily. Any type of household vinegar or even table salt in water can be used to antique brass. This can take longer to take effect than the other methods — several hours for vinegar, and up to several days with salt water— but you do not have to handle any dangerous chemicals and probably already have the necessary ingredients in your kitchen. Prepare the brass first as described above to ensure the antiquing succeeds. Wear rubber gloves for any method to prevent getting oil on the brass. Apply salt water to make brass slightly darker. A mix of equal parts table salt and water will oxidize the brass, simply speeding up the natural aging process brass undergoes. Apply it with a small paintbrush over the entire surface and reapply daily until you've achieved the appearance you enjoy. Coat with vinegar instead for more pronounced aging. Apply with a brush or simply dip the piece in any type of vinegar. Allow it to dry, then apply an additional coat if you'd like a darker color. Mix a spoonful of table salt into the vinegar for a greener patina. Heating the brass with a hair dryer or oven to around 450ºF (230ºC) will produce more noticeable results, but you'll need oven mitts or thick gardener gloves to handle it at this temperature. Use vinegar vapors for a warm brown appearance. This may not achieve the authentic appearance that ammonia or antiquing solution will, but some people prefer the "gingerbread" appearance that results. In any case, it is certainly safer and less expensive than those methods. Pour some vinegar into a plastic bucket with an airtight lid. Place wooden blocks or other objects into the bucket so a stable, flat surface is dry above the level of the vinegar. Place the brass on top of the objects. Seal the lid to trap the vinegar fumes and let them alter the brass for several hours or overnight. Whichever method you used, wash with warm water and dry. Once the result you want is achieved, which may take several applications, wash the brass in warm water. Dry it gently with a towel or by applying heat. Once it is dry, you have the option to preserve its color by coating with a brass lacquer or wax. To age brass rapidly, purchase an antiquing solution. This is the quickest of all methods, but it does require you to purchase a specialized product. These are sold as antiquing solutions or brass agers. The specific brand will determine the appearance of the antiqued piece, but the process should be similar regardless. Always follow the instructions for Preparing Your Brass before beginning any antiquing method. This is not a good method to follow if you're not certain that your piece is solid brass. See Using Vinegar or Salt Water instead. Use rubber gloves, safety goggles, and good ventilation. Antiquing solutions can be made with a variety of chemicals, most of which can damage skin and eyes or release toxic fumes. Protect yourself with basic safety equipment and open the windows before you begin. Be especially careful if your product contains any of these hazardous chemicals: ammonium hydroxide, glacial acetic acid, nitric acid, or sulfuric acid. Dilute the antiquing solution according to the manufacturer's instructions. Read the label carefully. Some solutions may not require diluting, whereas others require as much as 10 parts water to 1 part antiquing solution. Use room temperature water and mix in a ceramic or plastic container large enough to submerge the entire brass object. Do not use container made from other materials, as the acids in the solution could corrode them. Do not fill the container too full. Leave room to fit the brass object without the container overflowing. While wearing gloves, agitate the brass object beneath the surface of the antiquing solution. Hold the brass in the solution and move back and forth to dislodge air bubbles. Make sure the solution covers the entire object, but doesn't reach near the top of your gloves. Air bubbles that remain on the brass will cause bright spots where the brass was not aged. Turn the brass object in your gloves so you get even exposure to the solution. Watch the color change and pull out when the desired color is reached. It should take between a few seconds and a couple minutes to begin changing colors, moving from pink to red to brown to black. Pull it out when you see the color you're aiming for. If you plan to brighten your object with highlighting (see below), let it get slightly darker than the color you want. Don't worry that you'll ruin your brass. If you pulled it out too early, simply put it back and shake again. If you pulled it out too late, scrub with a scotch-brite pad or lightly with steel wool to remove the color so you can try again. Rinse the object to highlight (optional). Rinse with hot water and clean off the resulting white powder using a sponge or scotch-brite pad. This results in a brighter, accented object compared to the darker, even patina it had immediately after treatment. If you are trying to create a black or almost black patina, you'll have better results getting the patina to stay if you dip it in two or three stages, rinsing between each one. Dry evenly. Once you are satisfied with the color, immediately dry the whole object. Wet patches will dry darker than the rest of the surface. You may want to use a paper towel or rag, since some color could rub off onto it. Treat with lacquer or wax to preserve the current color (optional). Applying a brass lacquer or other brass finishing treatment will prevent the brass from aging further. This is recommended if the brass is handled frequently or if you want to preserve the current color. Apply ammonia periodically to produce the most natural aged appearance. Ammonia is a caustic substance that should be treated with caution, but it does come closer than any other method to creating the green brown appearance of naturally aged brass. Ammonia will eventually evaporate off the brass, so you'll need to commit to repeating this process every time your brass returns to its old appearance. How long this takes depends on the exact qualities of your object. This process will not succeed if you do not follow the steps for Preparing Your Brass beforehand. Buy ammonia and a sealable bucket from a hardware store. You'll need "full strength" or "clear" ammonia, not the dilute household ammonia more commonly sold at supermarkets. The hardware store is also a good place to buy a plastic bucket with airtight sealable lid, sometimes called "pickle buckets". For tiny pieces of brass, you can use a glass bottle with airtight cap instead of a bucket. Tie it with a cord and suspend it over a small amount of ammonia, screwing the cap firmly to hold the cord in place and trap the ammonia fumes. Wear rubber gloves, safety goggles, and work only in areas with excellent ventilation. Ammonia fumes are toxic and should never be inhaled. Work outside if possible or in a room with great air flow. Place a wooden block in the bottom of the bucket. You should create a stable, flat "shelf" large enough for the brass object to sit on. Use a piece of plywood for large objects, stacked on top of several pieces of wood to make it stable. Pour ammonia into the bucket. Keep the ammonia level below the upper surface of the wood. You don't need too much, although more ammonia may hasten the process. Place the brass objects on the wooden "shelf". Make sure they are stable and in no danger of falling into the ammonia. If they do, remove it with gloved hands and wash in warm water. Dry before returning to the wooden bucket. Seal the lid and check back periodically. Depending on the temperature and humidity, freshness of the ammonia, and exact characteristics of your brass, the antiquing could take hours to take effect. Check back every hour or so to see how its progressing, taking care not to breathe the fumes that escape the bucket. Open the lid slightly for a quick glance, then close it tightly to keep most of the ammonia fumes in. Let the brass dry in a ventilated area. Once the desired color is reached, let it dry naturally in an area with flowing air. Wax it if you want a more polished effect. The aging effect of ammonia is only temporary, so you probably don't want to lacquer the brass since you would eventually need to remove the lacquer to re-antique the brass. You can use the same ammonia bath to treat other brass objects, but not indefinitely. Eventually the ammonia's potency will be used up and you will need to replace it. 
Make sure the object is brass. Learn what to do if your object is not brass. If the brass is lacquered, remove it with nail polish remover. Pour hot water over the object after treating it with nail polish remover. If there is a thin protective film or no finish at all, wash with gentler materials. Dry completely before continuing. Use vinegar or salt water to antique your brass safely and easily. Apply salt water to make brass slightly darker. Coat with vinegar instead for more pronounced aging. Use vinegar vapors for a warm brown appearance. Whichever method you used, wash with warm water and dry. To age brass rapidly, purchase an antiquing solution. Use rubber gloves, safety goggles, and good ventilation. Dilute the antiquing solution according to the manufacturer's instructions. While wearing gloves, agitate the brass object beneath the surface of the antiquing solution. Watch the color change and pull out when the desired color is reached. Rinse the object to highlight (optional). Dry evenly. Treat with lacquer or wax to preserve the current color (optional). Apply ammonia periodically to produce the most natural aged appearance. Buy ammonia and a sealable bucket from a hardware store. Wear rubber gloves, safety goggles, and work only in areas with excellent ventilation. Place a wooden block in the bottom of the bucket. Pour ammonia into the bucket. Place the brass objects on the wooden "shelf". Seal the lid and check back periodically. Let the brass dry in a ventilated area. 