Today we read a very professional article to introduce how to anodize aluminum, I share it below and also you can see the original website link at the bottom.
Anodizing uses acid to create a corrosion- and wear-resistant layer on top of a metal. The process of anodizing also changes the crystal structure near the surface of substances, like aluminum alloy, which allows you to dye the metal a bright color.  At-home anodizing can be useful for projects like protecting metallic family heirlooms and old jewelry. It can also be a great at-home experiment to try with older kids. Just remember to take extra precautions with caustic substances, like lye and sulfuric acid, when you anodize aluminum at home, as these products may cause chemical burns if handled incorrectly.
1. Collecting Supplies
Buy some standard aluminum alloy metal parts. Anodizing works particularly well with aluminum, so, if careful, you can do it at home. Use small aluminum pieces to begin with so that you can submerge it in small quantities of acid.
- You can find small aluminum parts for this purpose relatively affordably from most home improvement stores, as well as online.
- During this process, the part that you are anodizing will function as your anode.
- Buy a thick plastic tub to submerge your metal. Choose a type of plastic that is extremely hard and durable. The exact size of the tub you will need depends on what you’re working with, but it should be large enough to hold your metal piece and the aluminum and still have some extra room for the liquids.
- Find some clothing dye at a local craft store. During the anodizing process, you can dye the metal almost any color using a standard fabric dye. This is the process Apple uses to color iPods. 
- You can also buy special dye for anodizing that may produce better results.
- Purchase the items you need for anodizing. You will need several particular pieces of equipment to anodize at home. Most of these items can be found at your local hardware or home improvement store. These include:
- A degreaser product
- 2 lead cathodes long enough to overhang your plastic bin
- A roll of aluminum wire
- Enough distilled water to fill your plastic tub
- Baking soda
- Rubber gloves
- Find places to purchase the hard-to-source supplies. For anodizing, you will need several gallons of sulfuric acid (battery acid), lye, and a constant power supply of at least 20 volts. The battery acid may be hard to find; however, it is usually available at auto parts stores. A large battery charger should work as a constant power supply.
2 Cleaning the Aluminum
- Wash your metal with soap and water. Cleaning off dirt and debris helps keep the anodizing process running smoothly, and reduces the chances of imperfections as you work. Wash the object you want to anodize using a gentle detergent and warm water. Then, dry it completely with a clean rag or paper towel.
- Apply a degreaser with a cloth. Following the instructions on the product packaging, use your degreaser to remove any additional oil from the product. Wipe it away as necessary, making sure that no product remains on your metal before you move to the next step.
- Dilute lye in water to create a scouring solution. In a small plastic tub, mix 3 tbsp. (44 ml) of lye in 1 gallon (3.8 l) of distilled water. Wearing a pair of rubber gloves, place the object you want to anodize into the lye solution. Allow it to sit for 3 minutes, then remove it and rinse it thoroughly with warm water.
- The lye will remove any existing anodizing on the surface of the metal. Once it is removed, water should pour off the surface easily, instead of beading.
- Wear rubber gloves whenever working with lye.
- Do not use measuring spoons or cups that are used for food products. The materials used in this process are toxic.
Setting Up An Anodizing Bath
- Place your plastic tub in a well-ventilated area. The tub should also be placed away from things that could be harmed during this process. Set it on a piece of plywood and/or a thick drop cloth in case of spills. A garage with an open door or a shed with all doors and windows open is usually a good location.
- For best results, do this when the indoor temperature is between 70 and 72 degrees Fahrenheit (21 to 22 degrees Celsius).
- Set up your power supply. Set it on a non-flammable material, like concrete. Use a multimeter, available from most auto supplies stores, to make sure your battery is working consistently.
- You will need to connect the positive wire from your battery charger or rectifier to a wire that will be strung to your aluminum.
- You will need to connect your negative wire from your battery charger to an aluminum wire connected to 2 lead cathodes.
- Tie one end of the long aluminum wire to your anode. 12-gauge aluminum wire works well for this use. Wrap it or connect it to the part in an inconspicuous area. If your anodizing a key, for example, you may wrap the wire around the join between the blade and the bow.
- The area of the part that connects to the wire will not anodize.
- Make sure it is very tightly wrapped for a more consistent charge.
- Wrap the middle of the wire around a thin piece of wood. The wood should be longer than your plastic tub. This will give you leverage to lift it out when you are done. Make sure you have extra wire extending toward your power supply after you wrap it.
- Test the wooden handle to make sure your aluminum part will be fully submerged in the acid mix, but not touching the base of your plastic tub.
- Set a lead cathode on each side of your tank. String aluminum wire between the cathodes and connect them together on your small wood plank. You will attach the negatively charged power supply to this wire.
- Make sure the wire connecting the anode does not touch the lead cathodes.
For more details, you can check : https://www.wikihow.com/Anodize-Aluminum
Enjoy it !