It is a desirable trait on statues and for architectural features such as the copper cupola atop the tower of Dalhousie University's Arts and Administration building in Halifax, Nova Soctia, Canada (picture). Indeed, copper(II) acetate was once used as a green paint pigment.
However, this phenomenon is not at all attractive when seen on older pieces of jewelry. Invariably called green gunk, it should be removed by using one of the following cleaning materials. These cleaners from your kitchen cupboard are best on metal such as the clasps. Glass (yes, Swarovski is still glass) and hard gemstones are fine too.
But do NOT use them for soft gemstones like pearls - these are easily damaged. Also on the no-no list are rhinestones due to their foil-backings or sterling silver and silver-plated metal. When in doubt, test first or just clean only the tarnished metallic portions. These simple remedies are acid based, so any glue or plastics in the jewelry piece will also likely be affected.
First remove as much of the green gunk as possible with a soft toothbrush - a baby toothbrush might work better for small pieces. Then apply a little with a cotton swab or tip to clean. Severe verdigris though may make the metal piece brittle and unsalvageable especially if it is a functional part like the prongs holding a gemstone or the clasp.
Lemon juice/VinegarThis is the most common remedy used especially for copper. Lemon juice (citric acid) has a less acrid smell and works faster than vinegar (acetic acid). If straight lemon juice is too runny, make a paste with a little water and baking soda added. Some people also use a combination of lemon juice and salt, again as a paste. For a short history of lemons and its uses, see this article. Vinegar also works but some people might find it too acrid for their noses.
Ketchup or HP sauceWorks great with copper although it can be somewhat messy if you overdo it. If you don't believe me, take a tarnished copper coin and leave it slathered with sauce for a while. Rinse it off and you will find a shiny new penny! A "magic" trick to amuse children, too. They work because both contain vinegar. Remember to rinse and dry, dry, dry! It is the moisture that helped create the green gunk in the first place.
Prevention is better than the cure - jewelry should really be kept in zip-lock bags to reduce future tarnishing. So ban verdigris from your jewelry box!
Original Post by THE BEADING GEM
Jewelry Making Tips - Jewelry Business Tips