Hobbies Fine Arts & Crafts How to Add a Patina to Metal Art Coloring Brass and Copper With Kitty Litter Share PINTEREST Email Print Auke Holwerda/ Vetta/ Getty Images Fine Arts & Crafts Arts & Crafts Painting Drawing & Sketching By Maire Loughran Maire Loughran Maire Loughran is a certified public accountant (CPA), author, and business owner. She has over 15 years' experience assisting new businesses. Learn about our Editorial Process Updated on 05/04/19 While metals like brass and copper are beautiful on their own, artists and craftsmen who work with them sometimes like to "color" the metals. Most often, what they mean by this is adding a patina to the metal. A patina is a colored film that sits on the surface, produced through the process of oxidation. Patinas Ever notice the cool green or blue color that appears on copper or brass over time? That's the natural process of the metal reacting to oxygen. The patina forms to protect the metal from further oxidation. Using a chemical process, it's possible to decorate different types of metal with hues ranging from green to blue to brown. This process accelerates the natural oxidation of the metal, allowing you to produce brilliant colors without waiting on Mother Nature. Oxidation Oxidation is something that occurs on the surface of a metal in the presence of oxygen. The chemical reaction transfers electrons from the metal to the oxygen molecules, creating a colored oxide surface. The effect can also be obtained by applying a chemical such as heated potassium sulfide or liver of sulfur. Even if you aren't experienced in metalworking or jewelry making, you have probably seen sterling silver that has a dull, matte surface. This is created by applying a chemical mixture. Safety Precautions Like using a torch, oxidizing metal is not an arts and crafts skill that you just pick up and start doing. Working with chemicals requires taking safety precautions. Any vapor coming from a chemical reaction that changes the color of a metal is not something you want to be breathing in. You don't want it coming in contact with your skin, either. For this reason, make sure you are wearing protective clothing, such as gloves and a vapor mask, before oxidizing metal. How to Oxidize Brass and Copper One of the easiest ways to oxidize metals involves cat litter or sawdust. All you have to do is add an oxidizing liquid to the mix. Before mixing any chemicals, make sure to put on protective clothing (vapor mask and gloves).Measure out 1/8 cup of salt, 1 1/4 cups of ammonia, and 3 cups of water.Combine these in a glass container that can be tightly sealed. You can use an empty canning jar or an empty jelly jar that's been cleaned.Use the mixture to moisten some cat litter—don't get it too wet or too soggy—in an airtight plastic container.Bury your metal in the cat litter. Place a few pieces near the top so that you can easily check on them. When you are satisfied with the patina, remove your metal from the mixture.To fix the patina, you'll have to apply Renaissance wax or spray acrylic. Otherwise, the patina will rub off the metal. Adding Color With Ink Another way to add color to metal is to use a brush-on opaque ink such as Vintaj Patina. These opaque inks are designed to adhere to metal, creating the illusion of a chemical patina. If you are short on time, or if you don't won't to go to the trouble of mixing chemicals, they are a great way to add some more excitement to your metal art.