Depending on the type of patina, you’ll pour or spray the patina solution onto the surface. Once you’ve decided, it’s time to begin! Start by dampening the surface of the item with water. Generally, vinegar or lemon juice will give a copper or brass item a greenish-brown patina, while chemical solutions such as brass or copper sulfate work best on steel items. ![]() Next, you have to decide which type of patina you want. Depending on the type of patina you’re trying to create, the surface could be wiped down with a suitable degreasing solution or left untreated. The process starts with cleaning the surface of the item you’d like to give a patina to. Making a homemade patina is relatively simple, and often done with vinegar or lemon juice. Heating copper in the presence of ammonia can cause a black deposit to form on the surface of the copper, but this is not the same as corrosion and does not cause the copper to turn blue. Copper normally has a reddish-brown color, but that can be altered by applying different electrochemical treatments or by heating the copper. Copper oxide is a black or brown powder that is formed when copper is exposed to air or oxygen, but it has nothing to do with ammonia. The blue solution may be allowed to settle, after which the solution can be filtered and water added to the solution to obtain an ammoniacal cupric complex that can be further reacted with organic compounds to produce organic compounds with copper attached. This complex is often referred to as the “ammoniacal cupric complex” and is stable even at higher pHs, allowing for the safe and efficient oxidation of copper by ammonia. ![]() As the process progresses, a blue solution develops as the copper ions interact with the ammonium ions to form the copper(II) ammonia complex. ![]() The reaction is favored by an acid solution, so the pH must be kept low by adding an acid such as hydrochloric or nitric acid. The ammonia molecule then takes up the extra electrons and gets reduced to ammonium ions. The hydroxide ions play an important role in the oxidation reaction they act as electron donors to the copper, which passes the electrons to the ammonia molecules and gets oxidized to copper(II) ions. The oxidation process begins when copper is in contact with an aqueous solution containing dissolved ammonia, usually in the form of ammonium hydroxide. Oxidizing copper with ammonia involves reacting copper with aqueous ammonia to create copper(II) ammonia complex in an ammoniacal copper(II) solution.
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