Introduction: Cleaning Badly Tarnished Brass, Bronze and Silver
This is a easy way to electrochemically clean up brass, bronze and silver items that are badly tarnished.
I have used it quite a bit to clean up boat hardware and items I have picked up while diving.
The method is simple, and leaves you with a nice clean item without having to do much work.
Brass, bronze and silver tarnish because the metal reacts with compounds in the surroundings. This can be oxygen, sulfur compounds, carbon compounds or chlorides.
The tarnishing actually preserves the metal below by sealing it in, so it can not react further with the surroundings. This is the effect that protects statues, and roof cladding that are exposed to the elements for centuries. Sometimes, however, we wish to remove this tarnishing, like in the example of the bronze handle pictured here.
One way to remove tarnishing is to use abrasives like sand paper or polishing creams. Any such mechanical polishing removes some of the metal every time you do it. This can be seen on old silverware, where the patterns and engravings are usually rounded and have lost detail.
The electrochemical way of removing tarnishing, that we use here, is gentler in this respect. In short terms it turns the surface metal back to its original state by removing only the compounds that reacted with it in the first place.
This is a good way to clean up detailed items, where mechanical polishing could cause damage. It could also save you a lot of polishing work if the metal is badly tarnished.
The simple theory behind this method is that different chemicals have different affinities toward each other.
Aluminum has a higher affinity for the sulphur, oxygen and chlorides mentioned above than brass, bronze or silver does, so when you put them in contact with each other, the atoms are going to recombine. In the end, you get tarnished aluminum, while the tarnish is removed from the brass, bronze or silver you started with.
To help the reaction run, we add salts as reactants, and use hot water to speed things up.
Be aware that this method removes all of the tarnish on your items, so on silver, you will also loose the tarnishing in the deeper parts of patterns and engravings.
Most of you have probably tried cleaning copper coins in ketchup or cola at some point in your life. This is a different type of reaction. In both cases the oxidised metal will react with the acid. For household use this is usually acetic acid (vinegar) citric acid (lemon juice) or tartaric acid. This is a very efficient way to remove tarnish, but similar to polishing, it removes metal and should be used with care on delicate objects.
Step 1: Materials
Use a container that is not made of metal. This is to ensure that your items don't react with the container. Glass, plastic, porcelain or enamelled containers are super.
Step 2: Start the Magic
Crumple up som aluminum foil and put it in your container.
Put the item you want to clean on the foil. The metals need to be in direct contact for this to work. For larger items, like this handle, pack the foil around it, so you get a larger contact surface.
Mix baking soda and salt with hot water and cover everything with it. The proportions are not crucial, but about 1 tablespoon of salt and 1 tablespoon of baking soda to 3 dl water should do the trick.
Lightly tarnished objects should clean up in a few minutes, and you just rinse them of and dry them.
For more heavily tarnished objects, you just have to give it some time. You will see tiny gass bubbles rising from the metal as an indicator that the magic is happening.
Now, the bronze handle I have used here is an extreme case. It has probably been laying on the sea floor for decades, and in addition to the tarnishing, it is encrusted in the carbonate shells of marine organisms and other forms of grime. This kind of cleanup requires some extra juice.
In this case, I also added some vinegar and a little dishwashing soap to the water.
The vinegar serves two purposes in this case. The first is that it dissolves the carbonate shells formed by different creatures over the years. The second is that it removes some of the tarnishing by reacting with the metal. In a solid object such as this, I'm not worried about the tiny amount of metal removed by this process.
The dishwashing soap is just there to help remove residues of oils.
Even this heavily tarnished and encrusted handle only needed three hours in the mixture to clean up completely.
As you can see in the third picture, it looks pretty much the same upon removal from the bath. The difference is that the grime no longer sticks to the metal. On the forth picture I have simply rubbed the grime of under running water with my fingers, and on the last picture, I have removed the last of it with a scrubbing sponge to reveal a nice and shiny bronze handle.
Instead of hours of polishing, this required less than five minutes of actual work to clean up.
This method does not leave you with a shiny surface in the end. To achieve that, you have to do some final polishing.