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The term 'passivation' refers to treating metal with chemical baths in order to make them permanently resistant to corrosion. In same cases, passivation is the name given to the application of anti-corrosives (instead of a bath) to various metals. The process that is used to passivate copper, however, is a little different, as there is no way to truly alter this metal through chemical baths.
The easiest way to passivate your copper items is simply by exposing them to the elements. Leave them outside for somewhere between four and eight weeks, then check to see whether a dull blue-green patina has begun to form. This colouring actually helps to prevent further corrosion from forming.
If you do not have the time to leave your copper outside for this long, you can accelerate the process by mixing a chemical bath. Add together just under three kilograms of ammonium sulfate, a third of a cup of copper sulfate, an eighth of a cup of ammonia and about 24 litres of water.
This solution should be applied to the copper as a spray and left to dry between each of its six applications. After waiting six hours, you should begin to see the patina deepening in colour. It will begin to spread around the item much faster, protecting it from further corrosion immediately.
As you can see, the only way to protect your copper items from corrosion is to allow them to corrode a little. It is important to take note, however, that this patina will not damage the copper in any way and, should you ever decide that you want to return the metal to its shiny glory, it can be removed with some thorough cleaning.