Alloys are made up of a variety of different metals , Zinc , Copper , Silver , Nickel, etc. It is the nickel that gives the largest tarnish problem but without it , the gold would not have the rich luster. There are other factors such as the type food you consume , body perspiration and the environment that you subject the jewelry to ,bleach , ammonia etc. Silver is a naturally tarnishable metal and will tarnish . Most jewelry on the market comes with a nickel or rhodium plate to enhance the finish and resist tarnish.
Silver tarnish is easy to remove by simply dipping in the right solution .
This could be a casting problem. Unfortunately with all the foreign non regulated imports coming into our country , this has become a real problem in the last 10 years. The news reports that have surfaced lately about under karating gold being sold is absolutely true and has been an issue of concern among legitimate jewelry manufacturers for several years. If you were having a ring made from scrap gold , the jeweler has no way of knowing what alloys were used in the original product or how many times the metal has been melted. Each time you melt metal , you loose some of the metal weight by converting it to a gas.