Noble patina. Fun chemistry experience at home

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Noble patina. Chemical experiments

Entertaining experiments in chemistry

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You have already learned how to make noble black on silver express method. Now we will learn how to get a noble patina almost as quickly.

Copper and bronze objects in humid air gradually become covered with a green coating; ancient candlesticks and door handles, mantel clocks and bronze statues in the squares turn green and darken. The plaque formed on them - the so-called noble, or antique, patina - is highly appreciated by art lovers.

In order for a patina to form, a long-term, over many years, exposure to air containing moisture and carbon dioxide (carbon dioxide) is necessary. In the presence of these two substances, a film of basic copper carbonate is formed, which is close in composition to the well-known mineral malachite. We will not succeed in obtaining the mineral artificially - it is impossible to reproduce its dense crystalline structure. But the creation of an antique patina will take us not years, but a matter of minutes, well, in extreme cases, an hour or two.

To a small copper object (and for a rough experiment it is even better - to a plate or a piece of copper foil) attach wires with stripped ends. Wipe the surface, as you have done more than once, with fine sandpaper, put the object in a hot solution of washing soda, rinse with water and immerse it in a weak solution of vinegar - this will help to avoid premature oxidation.

In the meantime, prepare the electrolyte: two teaspoons of ammonium chloride (ammonia) in a glass of water. Without touching the copper object with your hands, remove it with tweezers (or wires) from the vinegar solution, rinse under the tap and dip it into the ammonia solution. Connect the wire to the positive pole of the battery, and connect its negative pole to a copper electrode - to any copper plate that can not be cleaned so thoroughly. Soon the cathode, that is, the object on which we apply the patina, will be covered with a red matte layer. But let me, we were counting on the green!

Let's not rush, however. After ten minutes, remove the object without touching it with your hands, and put it so that water flows from it, but the surface is not scratched; you can hang it by wire. An hour will pass, and the red layer will turn green. This red patina on copper turned into green, similar to malachite.

An even greater effect can be achieved if an ammonia solution with a concentration of about 25% is taken as an electrolyte, but in this case it is necessary to work under draft or in fresh air, since a concentrated ammonia solution has a very pungent odor. Hang the object so that part of it is above the electrolyte. Then the part that is in the solution will remain red, and the part that is in the air will be covered in an hour with a small green-blue film, very similar to a real noble patina.

There is no need to rush, putting this experience, and increase the current: the slower the process goes, the stronger the layer of basic copper carbonate. But all the same, hours are not years, and our film is far from natural patina in strength (although it is no less beautiful). To save it, cover the green coating with some colorless varnish.

Author: Olgin O.M.

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