Forcing Copper Patina with Salt and Ammonia Vapor

Patina on copper and brass is analogous to rust on ferric metals, that is to say it happens when metal meets oxygen. Often times this corrosion is destructive, but can be used for aesthetic and/or protective purposes by forcing a certain kind of oxidation with specific techniques. What follows is a brief guide to my favorite method.

Materials

• Rubbermaid container or similar (at least somewhat) airtight container
• Wood, wire, basket, or other structure to support the copper in the vapor bath with minimal contact
• Paper towels
• Simple Green
• Household ammonia (10% solution of ammonium hydroxide)
• Cameo steel cleaner
• Granulated salt
• Misting/spray bottle of water
• Respirator rated for vapors/fumes
• Safety glasses (not pictured)
• Disposable nitrile gloves
• Disposable container and toothbrush
• Your copper items

Step 1: Clean the copper

Cleanliness is crucial to ensure the maximum amount of oxygen can get to the metal as quickly as possible. The fastest and easiest way I’ve found that brings good results is to scour the copper with a paste of Cameo and Simple Green, then rinse with hot water.

After cleaning, set the rinsed metal on a clean paper towel. Do not handle the copper again with bare hands until after the treatment is complete; always wear gloves. If a piece drops or touches a non-clean surface, scrub it again.

Step 2: Prepare the vapor chamber

For washers, I use scraps of wood with V-notches roughly cut. Don’t allow any flat surfaces to stay in contact; it will block the vapor and prevent patina. I’ve had success with larger/heavier objects in a steel steaming basket. You can easily improvise a way to suspend any sort of object in the chamber. The main rule is to keep minimal contact with the metal to ensure maximum contact with vapor.

Step 3: Wet & salt the copper

Using the spray bottle, thoroughly wet the copper, then sprinkle salt liberally all over it. Do this outside of the vapor chamber so as not to contaminate your ammonia with salt. When finished, return the copper to the chamber.

Step 4: Add ammonia to the chamber and cover

Put on your respirator before you open the bottle! You don’t need much ammonia; it’s the vapor and not the liquid we really need. I add about 1/4 cup, but just a few tablespoons would probably do it. Pour it carefully, down the side of the chamber. Don’t let it splash and don’t let it get on the copper. Put the lid on the container.

Step 5: Wait

Let the copper sit in the vapor bath until the desired level of patina is reached. I don’t get very particular about it, and just keep checking until it just looks right. I like a heavy patina and usually go for an hour or two.

Step 6: Remove from vapor, clean and finish

After removing from the vapor bath, thoroughly rinse off the salt and dry the copper. Lots of the very bright blue patina will flake off immediately. I hasten this and stabilize the patina a bit by giving each piece a brief rub with an oily cloth. I think this makes the patina look a bit more authentic, but I’d imagine there’s some sort of finish you could apply to better preserve the bright color, if you wanted to.

That’s all there is to it.

I should mention, this method works great on brass too!

Thanks for reading!

Jason