When you're buying gold jewelry you should know how much gold is in the piece you're buying. This is even more important if you're selling scrap jewelry to a dealer or Jeweler.  Otherwise you are almost certainly going to lose money in the transaction.

First gold and silver use a different weight system than our standard America oz.  The standard America oz used in foods, gasoline, etc., is called a avoirdupois oz and there are 28.35 grams to an oz.  In gold and silver these are measured by the Troy oz., which contains 31.1 grams to an oz.  So a Troy oz is MORE than an ordinary oz.  When you are buying silver and gold commerative items be sure to ask if the piece is being offered by TROY WEIGHT because if it isn't you use 28.35 grams for an oz rather than 31.1.  Example: Someone has a coin they are selling and they discribe it as pure silver or .999% which is accepted as pure. If they tell you simply it has 50 ozs of silver you need to know if its 50 ozs Troy or 50 ozs aboirdupois.  You will seldom run into anything gold or silver not offered in Troy but it does happen. 

When buying gold jewelry you can weight it yourself on a scale that gives you grams, then you can use this to deterine the gold content by taking the ctw (gold content) and multiplying the price of pure gold per gram X's the number of grams in the piece.  For instance if gold is selling for $900 an oz., you divide $900 by 31.1 to get the per gram price.  If the piece is 24K gold and weights 5 grams and the price of gold is $900 an oz then the per gram price would be $28.94 per gram.

24K Gold contains 100% pure gold, 18K is 75% pure gold, 14K is 58.3% pure gold, 12K is 50% pure gold and 10K is 41.7% pure gold. So before doing the match above you have to first determine the CONTENT of pure gold in the piece and you do that by multiply the K percentage by the weight of the piece.  So if the piece was 5 grams and it was 14 K gold then you would have 2.9 grams of pure gold then you multiple that by $28.94 (at the $900 per troy oz price of gold) to arrive at what the gold content of your scrap piece is or the new piece you're going to buy.  Fine jewelry is going to cost much more than just the price of gold.  After  all you're going to have to pay someone to fashion the jewelry, buy the gold to make the jewelry, sell the jewelry to a dealer and finally to you.  So you can expect to pay much more for the piece than the actually gold content and the more labor intensive the piece the more the cost.  But this will give you a good idea of what the worth of just the metal is and when you're selling gold it becomes very important to be able to figure out the price of your gold content.  Don't expect a buyer to give you the exact price of gold, he cannot make a living selling at the exact price but do expect 80% of the cost of your gold in any scrap piece and if that isn't offered go some where else. 

Sterling Silver is .925% pure

Please take the time to check if this guide has been helpful to you, thanks :-)