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NOBLE PATINA

 

Noble niello on silver you have already learned how to do the rapid method. Now learn almost as fast to get a noble patina.

Copper and bronze objects in moist air gradually covered with a green tinge; green and darken antique candle holders and door handles, mantel clocks and bronze statues in the squares. The formed plaque on them - the so-called noble or antique, patina - very appreciated by art lovers.

To form a patina, you need long, for many years, exposure to air containing moisture and carbon dioxide (carbon dioxide). In the presence of these two substances form a film of a basic carbonate of copper, the composition close to the well-known mineral malachite. Get artificially mineral we fail - unable to play its dense crystalline structure. But to create an antique patina we will take not years, but a few minutes, well, at least an hour or two.

Small copper subject (and to approximate the experience even better - to the plate or piece of copper foil) attach the transactions with stripped ends. Wipe the surface, as you did many times, fine sandpaper, place the item in a hot solution of washing soda, rinse with water and soak it in a weak solution of vinegar - this will help to avoid premature oxidation.

In the meantime enjoy cooking electrolyte: two teaspoons of ammonium chloride (Sal ammoniac) in a glass of water. Not touching the copper object with his hands, remove it with tweezers (or transactions) from the vinegar solution, rinse under the tap and immerse in a solution of Sal ammoniac. Connect the transactions to the positive pole of the battery, and the negative pole connect with a copper electrode with any copper plate, which can not be cleaned so thoroughly. Soon the cathode, i.e. the object to which we apply patina, covered with red matte layer.

But let me, we relied on the green!

We will not, however, rush. Ten minutes later, remove the object without touching it with his hands, and put it so that it was dripping wet, the surface is not scratch; you can hang it for posting. Will any hour, and the red layer will become green. This red patina on copper turned green, similar to malachite.

Even greater effect can be achieved if we take as the electrolyte solution ammonia concentration of about 25%, but in this case it is necessary to work under traction or outdoors, as a concentrated solution of ammonia is very pungent smell. Hang the object so that part of it was above the electrolyte. Then the part that is in solution will remain red, and the air, covered for an hour with a small green-blue film very similar to this noble patina.

No need to hurry, putting this experience, and to increase the current: the slower the process, the stronger layer of basic copper carbonate. But still, the clock is not years, and on the strength of our film is far from a natural patina (though not less beautiful). To save her, cover green cover with some clear varnish.

O. Holguín. "Experiments without explosions"
M., "Chemistry", 1986

 

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