Learn about PATINA

Patina is a film on the surface of bronze or similar metals (produced by oxidation over a long period); a sheen on wooden furniture produced by age, wear, and polishing; or any such acquired change of a surface through age and exposure. On metal, patina is a coating of various chemical compounds such as oxides or carbonates formed on the surface during exposure to the elements (weathering). Patina also refers to accumulated changes in surface texture and colour that result from normal use of an object such as a coin or a piece of furniture over time. Patina is like a growing algae. It will continues to grow as long as the metal of bronze and even cupernickel is expose to air and damp enviornment. Therefore, it is important not to place or keep your coins and antique to such areas.

I do have some modern coins exposed to such enviornment and begin to grow Patina. I have some Shekels left in my pocket when I visited the deadsea and I didn't took out to washed these coins.......today, these nickel coins has some patina coating.

Patinas are restricted to exposed surfaces and are fragile (that is, they can flake off). One reason bronze is so highly valued in statuary is that its patina protects or passivates it against further corrosion. This natural patina is solid and seldom shows a tendency to flake. Brass is also resistant to corrosion, but it is, in the long run, not as attractive since local pitting shows against the shiny background.

The photo I download from a web site that sell Knife coins........This color of Patina from the external appearance , I can tell off-hand that the Patina is a Fake patina.....therefore , the coin is fake as well. The fake patina doesn't match as what I described above on the characteristic of Patina.

You can do a simple test for yourself by scratching the surface of the coin.

Besides that, the imitation of the Inscription also poorly etching.

The word "patina" is pronounced PAT'n-uh (although puh-TEE-nuh has come into common use in the U.S.), and comes from the Latin for "shallow dish". Figuratively, patina can refer to any fading, darkening or other signs of age, which are felt to be natural and/or unavoidable.
The chemical process by which a patina forms is called patination, and a work of art coated by a patina is said to be patinated.

The green patina that forms naturally on copper and bronze is known as verdigris and consists of copper carbonate.
One example of a patina is a green surface texture created by slow chemical alteration of copper, producing a basic carbonate. It can form on pure copper objects as well as alloys which contain copper, such as bronze or brass.

Another type of Patina is called " Applied Patina"

Artists and metalworkers often deliberately add patinas as a part of the original design and decoration of art and furniture, or to simulate antiquity in newly-made objects.
A wide range of chemicals, both household and commercial, can give a variety of patinas. They are often used by artists as surface embellishments either for color, texture, or both. Patination composition varies with the reacted elements and these will determine the color of the patina. For copper alloys, such as bronze, exposure to chlorides leads to green, while sulfur compounds (such as "liver of sulfur") tend to brown. The basic pallet for patinas on copper alloys includes chemicals like ammonium sulfide(blue-black), liver of sulfur(brow-black), cupric nitrat (blue-green) and ferric nitrate(yellow-brown). For artworks, patination is often deliberately accelerated by applying chemicals with heat. Colors range from matte sandstone yellow to deep blues, greens, whites, reds and various blacks. Some patina colors are achieved by the mixing of colors from the reaction with the metal surface with pigments added to the chemicals. Sometimes the surface is enhanced by waxing, oiling, or other types of lacquers or clear-coats.