for precious metals, bar none, the best.
Many of our customers ask us how we can tell if something is gold before we do any chemical tests. Well, a lot of it is just by experience but there are a few things you can look for to help determine whether your item is made from precious metals. One of the first things we look for when sorting jewelry is whether any of the items are magnetic. There are only three ferromagnetic elements which are iron, nickel, and cobalt. If an item is magnetic it is because it consists primarily of one of those three elements which more often than not is iron. So the easiest way to sort through a lot of jewelry is to use a very strong (rare earth)magnet to weed out all the magnetic items. We use magnets out of old hard drives. Even if the item is slightly magnetic it most likely does not contain any precious metals.
Once we have removed all the magnetic items from the pile we then look for stamps and markings on the items. Nearly all precious metal jewelry has a mark of some kind. On chains the marking is usually on the clasp or right next to the clasp and on rings the markings are on the inside of the ring. Often times, people find the stamp but don't know what the stamps mean. We will go through each precious metal and list the most common stamps for different grades of gold. I am sure we will miss a few but this should help you get a better understanding of what it all means. Remember, just because it is old does not mean it is a precious metal.